Workflows¶
Quote
Design isn’t finished until somebody is using it.
― Brenda Laurel
Preface¶
In the "Workflows" chapter we break down the steps to make your IGMAS+ project smoother.
You will learn here how to handle project parameters, explore different displays and visuals for a better view of your model, and discover seamless methods of importing model geometry, as well as easy ways to save and load your work.
Let's simplify the process of getting things done in IGMAS+!
Setting up interface appearance¶
Before getting started, two more decisions related to the program interface can be made that is independent of the modelling process:
- the language of the interface
- the external appearance (interface theme).
Language¶
Click “Edit” in the TITLE BAR > select “Options” > and then “Language”:
Theme¶
Click “Edit” in the TITLE BAR > select “Options” > and then “Look & Feel”:
Importing horizons¶
This Workflow is used if existing digital data define continuous horizons in the entire modelling area.
Several horizons are stacked, the physical parameters between the interfaces are assumed to be constant.
Users must use one file for each horizon.
Before we get started, here are a few tips to make sure the input works:
File formats
The following formats are possible: *.xyz,*.csv or Geosoft binary grid format *.grd, see Manual Section 6.3 on page 132. Preferred is the file format *.csv.
Point types
The points defining the horizons may be gridded or irregularly distributed. Points with identical location but different z-values will be averaged (there will be a notice).
But beware:
- The points are interpreted to represent point locations x, y, z. They are not to be confused with grid cells, which are not used here, even in case of regularly gridded horizons.
- Make sure that the files are read in such a way that they always start with the top horizon. The order (from top to bottom) is very important, because it directly controls the triangulation. We will come back to this in a moment.
- Have you prepared the "correct gravity field"?
That means, do you want to calculate with a FREE AIR or with a BOUGUER anomaly?
In both cases a topography file must also be read in. Here you have to make sure that the model stations are NOT located inside the model masses - otherwise the mathematics behind everything will not work and the gravity will be calculated incorrectly.
- Make sure that the units are correct: give densities in \(kg/m^3\), gravity in \(mGal\) or \(10^{-5} m/s^2\), depths and lengths in \(km\) or \(m\).
- And finally: did you prepare your model data files for a plane gravity calculation (use UTM, Gauss-Krüger coordinates) or for a spherical calculation (use geographic coordinates with latitude and longitude)?
If all this is considered, it goes off, assuming that IGMAS+ is installed correctly.
How to import model geometry?¶
Choose File > New Project > Irregular/Regular Horizon (XY-Plane) Import. Choose the directory and the file(s) to be imported. Make sure to select all files for the model to be built, as later inclusion of additional horizons is not possible. This is how it looks like:
Press Finish 
Now you see the following mask:
On the right, the input files are listed with the horizons from top to bottom. Below that the "Folder name" is displayed and below that the file type.
Press Next
Der “import wizard” lists all imported horizons (files) and orders them from top to bottom according to the value Zmin. Make sure, that the list corresponds to the stratigraphic column / layering in your modelling area. We had already pointed this out above. If necessary, change the order using the arrows on the right hand of the wizard.
From left to right, the following information is displayed:
Name This name will be used as the name of the body below the corresponding horizon. Can be changed later.
# of points Number of points to be read from file (for information only).
Area Minimum x-coordinate, minimum y-coordinate, size in x-direction, size in y-direction (for information only).
Zmin Minimum depth of the horizon (for information only, the value is used to define the layer order.
Zmax Maximum depth of the horizon (for information only).
# of x-points, # of y-points This value is used to apply averaging of horizon vertices on regularly spaced locations. Default is 0 for irregular points and original number of points for grids (no averaging). All three coordinates (X, Y and Z) will be averaged using the block average method (see Section 6.1.4 on page 124). Alternatively, user can use x-spacing and y-spacing to set up the grid for averaging (see below).
x-spacing, y-spacing Instead of setting number of points one can set desired spacing and corresponding number of points will be automatically recalculated.
Hint:
The last four columns can be used for filtering of highly oversampled horizons. Sometimes seismologists provide Moho depths data in a resolution of 100 m x 100 m ;-)
Press Next
The next wizard defines the general model parameters:
You see:
Extend model borders. Check, if the model should be extended laterally, and specify the model extension (Range). Refer to Section 5.10 on page 121 to read more about the model extension.
Minimum vertical distance. Minimum thickness of bodies. It is used only if the imported vertices have identical horizontal positions throughout all horizons or if the vertices are interpolated regularly on the sections (see Project Points (Mundry) below). In our example it is 2.2 m.
Z-Top. Depth of the upper limit of the model (plane, horizontal). Default 0, if no topography is given, otherwise maximum Zmin of all horizons. In the example input file, there is no topography in the model.
Z-Button. Depth of the lower limit of the model (plane, horizontal). Default: minimum Zmin value of all horizons. The biggest depth is 400 km (upper mantle); this is the bottom of the density model – set by the user.
Units. Make your choice depending on the data entered (depths, distances, grid spacing, etc.). Here we used “km”.
Project Points (Mundry). Interpolate irregularly spaced horizon vertices on the sections to be build. Default is: no.
In our model, we wanted to re-interpolate the data ("even" grid spacing). For this purpose a procedure according to Mundry is used.
Press Next
Almost done: In this last wizard we are able to specify the area to be modelled and the position of the vertical sections.
By default, the modelling area is the maximum area, which is covered by all horizons - indicated by a grey rectangle. Five vertical model layers are given by default. The first and fifth/last are hidden by the frame. They will be visible in the next image. The numbers at the border indicate the coordinates - in the example these are UTM coordinates.
Green dot___Defines the max. south-west corner of the modelling area.
Red dot_____Defines the max. north-east corner of the modelling area.
You may change the position of the circles by either clicking with the right mouse button on them (alphanumeric input); (an example for the coordinate input of the red point you can see here):
or just dragging them. Both input options redefine the model boundaries, also change the spacing of the five specified vertical planes (dashed lines in the window between the coloured points.
Azimuth, N – E – S - W. Sometimes the horizontal direction of the vertical sections must be adapted to the gravity field to be examined, because the modeling should ideally always be as perpendicular as possible to the main strike of the anomaly - this ensures the greatest possible model gravity effect. You have the possibility to set a first rough adjustment of the direction via North - South - East - West.
West: the vertical sections run in N-S-direction
South: the vertical sections run E-W-direction.
In our example from the beginning, the vertical sections are aligned in the west-east direction and count from south to north.
If you want to rotate it even more precisely, use the alphanumeric input in the azimuth window of the setting. In the example in the next figure, 283 (270 + 13) deg. has been used.
Distance. The vertical sections to be created are indicated by dashed lines. Use the alpha-numeric input to modify the distance between the vertical sections. Specification in km (as defined above for the input units). In the example, this would be approx. 317 km (316.85 km).
Count: Use the \< and > characters to decrease or increase the number of layers.
Press finish
... and VOILÁ, our model appears in the IGMAS+ main window, defined by the 10 vertical planes in the central part of the model and additionally a bounding section in the north and in the south - as it was entered earlier in the 2nd wizard window (above).
The model can now be moved back and forth for viewing. Click into the model with the right mouse button and keep it pressed. In this combination, move the model in the window. Moving the mouse wheel changes the zoom.
Note:
The colours of the stratigraphic layers are set automatically by the program. How to change them is shown below (refer to Colors). We still have no stations, no reference gravity field and the model densities loaded.
But we can already have a quick look at the vertical sections. If you are interested, go straight to the item “show vertical cross sections” below and return later to this position.
How to import reference gravity/gradient/magnetic field and topography/bathymetry?
Use the File > Import > Stations
Be sure to use the correct units and file type (.csv or .xyz)
In this input window you have the chance to assign different input parameters to the individual columns X - Y - Z. Column Z could also contain gradients or a magnetic field size. "Measured z component" is selected correctly.
Press Finish 
The stations are placed in red on top of the vertical cross sections.
However, we do not yet have a basis for calculating the model gravity field. For this, two steps are necessary for preparation.
(1) Triangulate the vertical cross section, which results in a true 3D structure.
IGMAS+ offers the user two options:
Press either in the TITLE BAR > Edit > Model - Triangulation
or Press in the TOOL BAR 
Next you will see this wizard:
Press Next
… and get from the program the following information:
PRESS Finish
In the status information (below) the message will be shown that your model has no errors (green light), and we can proceed to calculate the modelled gravity field.
To calculate the modelled fields, IGMAS+ offers two possibilities:
Click in the TITLE BAR >Tools > Calculate Anomalies
and select Calculate Anomalies.
or
press in the TOOL BAR 
and see the window:
Select the field component you will calculate and then
PRESS Finish
Of course, the length of calculation time depends on the size of the model and the number of stations. Be patient with large models!
The green "traffic light" of the "progress bar" in the “lower status line” gives you the certainty that everything has been calculated correctly.
… then the time has come to see the modelled field and the model in perspective on the screen.
Very well done and that's done for now… 
Saving a project¶
Before we start to explore the model, the fields and their possibilities for representation, we should learn how a model and its fields are stored.
This should be done from time to time by the user himself.
IGMAS+ offers two types of storage (see below):
- SAVE PROJECT and
- SAVE AS ...
(1) The SAVE project action is initiated by a click in the TOOL BAR > “SAVE PROJECT”.
A window will appear warning you not to overwrite the current model version. If this is desired, click 
IGMAS+ will create a new Model INPUT. Loading a model file in the next working phase you see that in the Timeline appears the former model (in green colour) and the new model blue shaded:
If you click No, nothing will happen and the model will remain. CANCEL will terminate the action without any decision.
(2) There is a second possibility to save model changes.
Click on “File in the TITLE BAR*
In the pull down menu appears (short key is “Strg+S” bottom).
“Save project” will save the entire model as already described above in (1).
enables the user to give a new name to the model output.
Click on the “create a new folder symbol” 
, rename the new folder and press “Save”.
The small symbols indicate from left to right:
From left to right:
Go one level up in the folder hierarchy - Go to home directory - Add a new folder - Show folders - Show folders listed.
Loading models¶
In the reverse case of loading a model that has already been saved, first select
“Open Project”.
Open a version
When opening a project, several versions are displayed. These are all versions that have been saved earlier.
Select the following:
Note
Dark or light interface appearance can be set by the user.
... and this also brings us to the next point in familiarizing ourselves with IGMAS+:
Displays & visualization¶
Above, we have already introduced the 3D view. If you want to go through the model step by step (vertical cross section for vertical cross section) then select on the IGMAS+ TOOL BAR under "Add Views", the item 2D View.
Add view > 2D View > click 
... and immediately the vertical section appears in the IGMAS+ Workspace window. Use pull-down menu “Add View”, select “2D View” and the 2D view appears in the headline below the icons and the first vertical cross section of the model is displayed.
There are several ways to step through the vertical sections of the model.
(1) Use the ˄ (up) and ˅ (down) in the right upper part of the main window to step through the model.
Now let's learn about two other options:
(2) Open the sections in the "OBJECT-TREE" window of IGMAS+ and select the section to be visualized (for example section 7). Click with the right mouse button on the section symbol and select "View Section/2D" in the window. The selected section will appear. Because each section must be clicked individually, it will take longer to view large models than with the method described above.
The third possibility to visualize sections is realized via the "Map display".
Add view > 2D Maps View (click)
Then the three maps appear that are active in the Object tree under "Fields".
Then the three maps appear (measured - calculated residial field), which are active in the object tree under "Fields". From left to right you can see the map of the measured field, the modeled field, and the differences between the measured and the modeled field.
A map enlargement can be seen in the next figure. Click with the right mouse button on the map layer and the window that opens offers the possibility to draw the section (click "Show sections").
NOTE: In the same way, other information can be selected in the same window.
For example, "Show Stations", "Show Contours", etc.
Click on one of the lines/vertical sections. It will be highlighted in red and the section name will be displayed.
Clicking with the right mouse button on the selected line opens the 2D view of this section.
The default setting is always the perspective display of the reference field (measured field). The default setting is always the perspective display of the reference field (measured field). This can be adjusted by clicking the following button in the TOOL-BAR line:
Add view > 3D Model > click
If the display of the comparison field is not desired, the user has the option to change this in the 3D display. In the following the difference field is to be represented. A right mouse button click on "Residual Field" opens the window and one selects "Show in 3D":
If you want to visualize the underlying information (e.g. positions of sections), you can change the transparency of the field display. Go to "Fields" in the OBJECT TREE and activate "Property Editor" in the BODY MANAGER below.
Here you can change the transparency (using the slider). In addition, a "shading" of the surface can be created and an exaggeration of the field.
The value for exaggeration is always smaller than 1: ValExagg \< 1
Perspective of 3D Model¶
The 3D model can be displayed in two perspectives. The default is the perspective view. Modification: click with the right mouse button in the model and select "View" in the window and select the perspective with the left mouse button:
A second, alternate procedure is:
Go to the line below the “TOOL BAR” and click the shown options for model perspective:
If all three types of display are selected, you will see below the TOOL BAR:
The three windows can be removed again by clicking on the X.
Zoom in, zoom out, move and place IGMAS+ elements¶
Click in the workspace window on the object to be enlarged/down sized.
- ZOOM in with a movement of the mouse wheel t o w a r d s the user,
- ZOOM out with a movement of the mouse wheel a w a y from the user.
This is generally true for all three "views:
But click for 2D View in the model.
Click with the right mouse button on the object and moved it pressed:
Moving objects of: 
Click with the right mouse button on the model and moved it pressed up and down, to the left and right. The window with the field curves will be placed correctly above the model.
Tilting a 3D View in its actual position: 
Click with the left mouse button in the workspace window and moved it pressed:
Center objects
Center model and 2D map views:
Click with the right mouse button in the model, select "Center at" in the window and select the perspective with the left mouse button:
A second, alternate procedure is:
Go to the line below the “Tool bar” and click the shown options for centering the model:
Center 2D View:
Go to the line below the “Tool bar” and click the shown options for centering the 2D cross section:
The cross section (lower panel)) together with the field values above it (upper panel) is centered in the area where stations are located.
2D View Section front/back side
In vertical cross sections that show the geometry of different bodies on their front and back sides (also called: double occupancy), the two icons of the following figure determine whether the front side (left icon) or the back side (right icon) should be shown.
Change model geometry¶
If changes to the geometry of the model become necessary, the user can make model adjustments based on changes to model vertices.
The actions Insert - Delete - Move vertices are described here.
Insert a vertex:
Press key I-key 
and navigate with left mouse button on the position of an interface/horizon > click .
Delete a vertex
Press shift key and navigate with left mouse button on the vertex > click 
.
Be sure to see the coordinates of the vertex to delete on the screen:
Shift a vertex:
Press shift-key 
and navigate with left mouse button on the vertex to be shifted > click 
.
Shift grouped vertices:
Press shift-key 
together with the key 
. Then define region of vertices to be shifted by open a window with left mouse button and move pressed left mouse button into the new position
Release the left mouse button. This is the result:
The model gravity field is automatically recalculated.
Split a body/polyhedron on a specific vertical cross section¶
Select "2D maps view" 
and mark in the map the cross section on which the density of the body should change (in ascending section number order). Here section 10 was selected; it is marked in red.
Alternatively, the vertical section can also be selected (1) in the OBJECT TREE or (2) by the "section up & down":
Click on the body to be divided (e.g. astenosphere) with the right mouse button and select "divide body".
The "divide body assistant" appears with the new name “Astenosphere new”.
Click "finish"
In the PROPERTY EDITOR (lower left window) the list of updated bodies with their properties appears (here “volume” and “density” are selected).
(1) The newly inserted body (Astenosphere new) still has the same density as the old one. The color has been selected by the program and can be changed by the user (see section "Colors").
(2) Check the topology of the “new model”. Select Tools in the TITLE BAR and select “Check Topology”:
If now “error” is detected (normal case) continue with the next step. You may notice that the PROGRESS BAR (traffic light) indicates red light:
Explanation:
The model has been changed and both triangulation and modeled gravity are no longer correct. Start with:
(3) “Model – Triangulation” to the new model. Select Edit in the TITLE BAR and select “Model-triangulation”:
Alternatively, the 
icon can be used for model triangulation. Go to the TOOL BAR line and select .
(4) Re-calculate the gravity of the “new model”. Select Tools in the TITLE BAR and select “Re-calculate Anomaly”:
… and the PROGRESS BAR (traffic light) indicates green light.
If necessary, change density of the new body by “double click” on the density value and insert a new value:
PROPERTY EDITOR**
> Body manager > double click” on the density of the new body
**
Voxel Cube¶
The use of a voxel cube (density cube) also fits into the thematic environment of density changes. In IGMAS+, a voxel cube is a cube consisting of many sub cubes. The size of the cube as well as the size of the sub cubes can be specified by the user. For example, think of a velocity cube in 3D seismic. Quite analogously, the 3D density cube is used in IGMAS+. The densities of the cube overlay the densities of the polyhedra/rock bodies in the three-dimensional modeling space. A typical application would be to define a depth-depending or laterally changing density function to a sedimentary body, as shown in the figure below: the grey colors indicate varying densities for the underlying rock density.
The voxel function may also be used to calculate the anomalies of an imported seismic velocity cube, applying a function for the conversion of velocities (normally Vp) into densities. If only the effect of an imported voxel cube has to be calculated, the simplest IGMAS++ model, a cube, might be defined with constant density ρ = 0. Refer to the following figure for basic information and to the IGMAS+ User Manual page 104.
Import/export and delete a voxel cube¶
Select File in the “TITLE BAR” > click Import > select VoxelCube > click with left mouse button on it 
.
Navigate in the new “Open” window to the directory where the file with the voxel cube is stored.
IGMAS+ provides several possibilities for navigation by the small icons at the right side of the directory pull down menu:
These icons allow the user to do the following – goto/show:
- Up on level -
- Home
- Create new folder
- List
Details:
Of course, you can also navigate to the desired directory with the ▼ next to the folder name; see next figure.
The “Open” window provides important information and enable the user to check the input data:
Does your voxel file have the extension “xxx.vxo”? If not, rename file before you continue!
Ensure that units of voxel positions (x,y,z = depth) correspond to units of polyhedrons (either in meter or kilometers > or feet). Select units in the pull-down menu “units” on the upper right of the “Open” window.
Leave all other settings as they are: for “Acceleration” (gravity field), “Gravity Gradient” and/or Magnetic Field.
In the next menu item of the OPEN window, the user decides how to proceed with any unoccupied voxel cube elements. The default action is "Fill empty cells with nodata value". This means that IGMAS+ inserts numbers with unrealistically high values (e.g. 1039) at the corresponding positions in the cube. If the alternative "Use interpolation to fill empty cells" is selected, corresponding values in the cube are interpolated.
The use of a CSV setting is strongly suggested. The separation of the values is indicated with "blank" in the example. In the following it is still determined whether a header is placed ahead of the data of the voxel file ("Interprete Header") and/or whether the cube values are separated with quotes ("use Quote for Values").
A few lines of the voxel cube input is given as an example for visual inspection.
The columns contain from left to right: x-, y- and z-values (depths) of the voxel elements; note the direction of Z: it is negative downwards . The last column shows densities of voxel cube elements.
Here all lengths are given in km!!! Click on “km” 
to select the correct unit.
Otherwise, the data in the voxelcube file will be read in meters, with the consequence that the size of the voxelcube does not match the size of the density model: the voxelcube becomes too small by a factor of 1000 per unit length.
If all input boxes are filled in, click on Open with the left mouse button.
You get the window and sect “Density type” for gravity modelling and “Susceptibility type” for magnetic modelling; click “Next” :
You get the window “Model Voxellisation” which contains further specifications regarding the use of the voxelcube in the context of combined Polyeder/Voxelcube - modeling. In the following INSET we explain the resulting possibilities for a correct 3D modeling.
INSET VOXELISATION
The Voxelisation is an important part of modeling with IGMAS+ and is quite different from other software packages > for modeling potential fields. For example, it is possible to realize very elegantly 3D density changes with depth (for example by compaction). The Voxelization function allows the user to take over a seismic velocity cube 1:1, whose velocities (Vp) in densities are performed by means of self-created or predefined functions in the software.
We start with a textbook example which was elaborated by Sabine Schmidt (February 15, 2023):
On the right side of the above figure, a density distribution is given in t/m3 (2.6 - 2.4 - 2.8). This corresponds to reality (blue, Real world). The middle figure shows the modeling conducted for this purpose (yellow, Model: Polyeder). We recognize that the density distribution with 2.9 was modeled at a lower depth - thus outlining a deviation from reality. This deviation can be corrected by blending a voxelcube model with the polyhedron model. This could have been determined from independent measurements and contains the densities 2.4 - 2.6 - 2.4 -2.8).
IGMAS+ allows the user to blend the voxelcube and polyhedron model with a special input function. The voxel function is called:
*** "cellvalue - density" ***
and corresponds to the import of a voxelcube with density differences, which, however, are determined by the software > independently of the user.
In the voxelcube domain, the "effective" densities are then obtained from the superposition of the polyhedron and voxelcube models: the left side shows the difference formation, the right side the superposition of both for the two models.
The superimposed density model has the same effect as the "real world" density model. We call this "hybrid modeling" and take advantage of the fact that the total density of all masses corresponds to the superposition principle. By dimensioning the voxel size, extremely fine tuning can be achieved within the 3D density model. The computation of millions of voxels is possible without lasting disturbance of the interactive processing or very long computation time.
Let's move back to the description of the voxelcube input (voxelization window).
The window for Model Voxelisation
For all geological bodies, special procedures for the use of the voxel cube can be defined here. Of course, this is only the case where the voxelcube covers the polyhedra. If this is the case, minus density can be entered directly after "cellvalue"; cellvalue contains the density element of the voxelcube element:
When entering a function, the user is supported by operators, mathematical functions, and the definition of constants.
It is also possible to use pre-defined functions (to convert velocities into densities such as the Gardener and/or Nafe & Drake - relations . These are provided for dimensioning the model in "meters/second" or "kilometers/seconds" and are used for the conversion of seismic velocity models into density models. Click the three small dots.
It is also possible to formulate your own conversions and calculations using the instructions provided.
In the lower part of the voxelization window there are still three input possibilities to be explained:
(1) Equation Settings, (2) Unit and (3) 
(1) Equation Settings allows the definition of a voxel function for
A L L geological bodies in the model. This is only useful if the voxelcube really covers all bodies.
(2) Unit: Here the units for the voxelcube densities are defined. Attention: the definition must not be forgotten, otherwise the model gravity field will not be calculated correctly.
(3) 
Here all those bodies can be hidden altogether (or switched on again), which are not covered by the voxelcube.
When all is defined, click FINISH 
Later changes of voxelcube functions¶
Regardless of the equation specified when importing the voxel (refer to the explanations before), the original cellvalue is always saved and can be changed manually for each body independently later.
Select in Interfaces of the OBJECT TREE the body whose the cellvalue function should be changed (29_Mantle in the example) and click:
In the PROPERTY EDITOR body 29 is displayed with the
Body name
Voxel equation: cellvalue-density.
If the user will change this function, click on the three small dots and an other window for the new input will be opened. If you like, change cellvalue by the definition as before.
Export a voxel cube¶
Select File in the “TITLE BAR” > click Export > select VoxelCube > click with left mouse button on it .
In the Save window select the folder where the voxel cube will be stored under the user specified file name. Press “save” 
.
Delete a voxel cube¶
If you want to delete a voxel cube or replace it with a new (updated) one, click with the right mouse button on the letters of "VoxelCube" in the "OBJECT TREE": the "Remove" window opens. Click with the left mouse button in the window and the voxel cube will be deleted from the model visualization (Screen).
However, the gravity effect of the voxel cube is not yet eliminated from the overall gravity field of the model. The next section explains how to delete the gravity effect of the voxel cube from the modeled gravity field. See the section "Use/invert Cube anomaly" at the end.
Voxel cube effects and their visualization¶
Information about the voxel cube can be obtained by clicking on "VoxelCube" in the "OBJECT TREE" and then activating the PROPERTY EDITOR (window at the bottom left). Click on VoxelCube then you see this screen
:
The window shows the name of the used voxel field (in light grey). The “Transparency” slider controls the transparency of the voxel cube in the “WORKSPACE WINDOW”.
- “Cube Type” indicates either a density or susceptibility voxel cube.
- “Algorithm” provides information on the calculation of voxel cube effects. In the example above a Newton Fast Fourier (Newton FFT) method is set calculating on multi cores. This is a fast and normal procedure. More information/other methos are available if you press the three small dots right of “Algorithm”. The “Voxel algorithm Wizard” opens:
We read that a CPU multicore implementation is active and the (gravity) effects of mass points are calculated in the wave number domain (FFT).
- Newton mass points calculation by OpenCL or
- Prism calculation (both multicore and OpenCL) or
- Gauss Quadrature (both multicore and OpenCL) even
- Spherical Newton mass point calculations are available if calculations are spherically done.
One can also extend the FFT grid.
If you click in the “Voxel algorithm Wizard” on the item “Interpolation Type” (Refer to the last image, left side) the types of interpolation are listed. An interpolation is necessary to transfer the calculated values at the FFT nodes to the measuring stations.
There are three methods to choose from:
- Kernel (3x3) Mundry interpolation,
- Nearest neighbor and
- Kernel (3x3) average interpolation.
Kernel (3x3) Mundry interpolation is robust and reliable.
If stations are located in a constant height, click on “Use Constant Station Elevation”.
Click “Finish” 
Activate “VoxelCube” and go to the “PROPERTY EDITOR”
The item “Use/invert Cube anomaly” in the PROPERTY EDITOR plays an important role. If it is “true”:
the gravity effects of the voxel cube and the polyhedrons are calculated at all stations; if it is “false”:
And the gravity of the polyhedrons will be calculated without the effect of the voxel file.
Modify model parameters (densities/susceptibilities)¶
We already knew this action when it came to changing the density/susceptibility of a new body (see also " Split a body/polyhedron on a specific vertical cross section ").
Change densities/susceptibilities¶
Select in the window of BODY MANAGER / PROPERTY Editor (bottom left) and select Body manager.
The names of the existing model bodies are displayed with their selected colors. Then follow from left to right "voxel factor", "density [t/m^3]", "volume voxels [km^3]" and "volume polyhedron [km]". What of this information is displayed, the user can specify
by clicking the small 
in the right corner.
The various parameters can be changed in their horizontal position: Click with the left mouse button on the parameter to be moved and drag it to the desired position with the mouse button lowered.
Double left mouse click on the body (here upper mantle) where the density/susceptibility is to be changed and type in the new density alpha-numerically.
The definition of „reference density“ is import because it minimizes the edge effect” of the model. Always set the reference density so that the edge effect is a minimum! Try this out on your model.
Density Inversion¶
Besides the possibility to change densities directly by the user, IGMAS+ also offers the possibility of an automatic calculation (inversion).
The MMSE method is used in IGMAS+. MMSE stands for “Minimum Mean Square Error” and utilizes the mean square approach and Gaussian random variables within a statistical framework.
(Refer e.g. to: C. Haase, Dissertation, Uni Kiel, 2014:
Select in the TITLE BAR “Tools” among other important program activities – we already know – klick on “Parameter inversion (MMSE). Here is what you see:
The next window opens:
First, one has the possibility to select the density-inversion by means of Gravity and/or Gradients”; with “Magnetic” one would make an inversion of susceptibilities (no susceptibilities exist in this example); refer to figure above.
To modify the error given for the field(s) (here 0.2 mGal) refer to scenario “Change error of measured fields” in last wizard.
At the right side of the above window, under the tab "IGMAS effect", the inversion of densities of polyhedra is to be selected (figure above). To set and/or to modify the standard deviations for the different densities in the menu above (STD: 5.0 t/m3) refer to scenario “Change standard deviation of densities/susceptibilities” below. For the inversion it will be sufficient in most cases to leave the values (STD) unchanged.
Otherwise, the densities of the voxel cube “Voxel Effect” can also be inverted (next figure).
To set and/or to modify the voxel factor (here 1.0) and the variance/STD 5.0) for the different bodies in the menu above refer to scenario “Change standard deviation of densities/susceptibilities” below. For the inversion it will be sufficient in most cases to leave the values (“voxel factor” and STD) unchanged. The “voxel factor” is explained in detail in the scenario “Voxelcube).
Below under “settings” you can switch off or switch on 
the of geological bodies listed above.
Invert the densities of polyhedra “4Astenosphere” and “reference” (under IGMAS Effect). All bodies under “Voxel Effect” are disabled now:
Click Next and the result will be presented in the next window :
Click Finish to accept the new densities
The upper panel lists the densities before and after the inversion and the lower statistics panel shows the standard deviations (before/after) and the Pearson correlation coefficients. Since the correlation after the inversion is better than before, the result of the inversion was accepted.
In the other case, by clicking on "Previous", the user would have the possibility to select other bodies, respectively to change the standard deviations and errors.
To change standard deviations and errors, the inversion must be canceled. It is not possible to change the above parameters in the inversion window.
Change error of measured fields¶
Click in the OBJECT TREE on “Gravity z-component”. Then select Property editor
And select one of the icons 
:
Click on “error gz” and then on “Value”. Double click with left mouse button
Enables the user to input a new value for the error of measured gravity field.
Change standard deviation of densities/suceptibilities¶
Click in the OBJECT TREE on “Gravity z-component”. Then select Body Manager.
You will see a window like this; (be aware: this here is only a snippet):
In the next step it is important to move the displayed parameters so that the items to be changed are visible. To do this, the window can be enlarged (keep the left mouse button pressed on the right edge of the BODY MANAGERS and drag it larger...).
Then, by clicking the ICON above right corner, a selection of the parameters can be made. Now it is important that Standard deviation is selected - for the density or for the susceptibility.
This results in the next screen:
… and after moving/sorting the parameters by pressing left mouse button and moving them into another position in the BODY MANGER, we see:
To select a new Standard deviation for the density/susceptibility of one of the geological bodies
> click on the body > and then on “Add Parameter”
In the small window that is displayed you may select the correct units (here t/m^3) and the type you will change: “Density Standard Deviation”:
... finally double click with the left mouse button on body and include the new value:
In the same way, the other parameters can be changed - for example, the "Voxel Factor", which can also be inverted. In this case, the "Voxel Effect" tab must be activated in the "Inversion" window (see "DENSITY INVERSION" above).
Colours¶
Colors are used in IGMAS+ in two very different areas:
- (1) For the differentiation of bodies (geological structures) or
- (2) in the map representation of the used fields.
For the differentiation of bodies (1) the program distinguishes between two color schemes:
- either the (geological) bodies are filled according to the colors known in geology (e.g. blue for Jurassic, green for Cretaceous and yellow for Tertiary rocks) or
-
the colors are determined according to the density of the body. Blue colors correspond to high densities of rocks, brownish colors to low densities.
This color spectrum is automatically set by the program and is based on the color scale used to create the residual gravity maps. In the current IGMAS+ version, the user does not have the possibility to change the scaling or the colors of the color scale. You can see the color palette (Vik) here; the way to get there is described in this chapter below.
Change colors for geological bodies/polyhedrons¶
Be sure to have selected the “Normal Color Mode” after clicking View in the TITLE BAR > “Body Color Mode” in the popped-up window > and set “Normal Color Mode”.
If the colors for the susceptibility of the bodies are to be set, then of course "Susceptibility Color Mode" must be selected in the window shown above. The process is analogous to the selection of the "Normal Color Mode".
Select “Add View” in the TITLE BAR and klick on “2D View”. Below the TOOL BAR the icon for “2D View” is set:
Then go to the “Object tree” (top left), click on 
to open the "Interfaces" tree
and select the body whose color is to be changed (here: 032_con_Sed_Po; blue bar):
... go to the „Property Editor“ > click in the opened menu in „Body“ and „Color“ > click on the small color window and click on the three grey points 
:
The color is also identified in the RGB color scheme (R:102 - G:204 – B:255).
Clicking the three grey points (figure above) this window popped up:
Select by clicking a new color :
Alternatively, the colors can be changed in this window using the HSV - HSL - RGB - CMYK color scales. The effect is the same everywhere.
Change colors for IGMAS+ maps¶
The color palettes used in IGMAS+ for map display follow new findings regarding the physiology of perception of healthy and visually impaired people (see for example:
https://theconversation.com/how-rainbow-colour-maps-can-distort-data-and-be-misleading-167159.
IGMAS+ uses two options for selecting different color palettes for displaying the comparison field (measured gravity/magnetic field) and the modeled field (calculated) on one side and for displaying the residual field on the other.
Selection of the color palette for measured and modeled field¶
Select “Add View” in the TITLE BAR and klick on “2D Maps View”. Below the TOOL BAR the icon for “2D View” is set:
Three maps are shown:
Measured field (left) ------------------------------------------ Calculated field (middel) ---------------------------- Residual field (right)
Select below the TOOL BAR on the right upper corner the icon 
and select the tab “meas Gz/calc Gz”.
Get a window which visualize the Batlow palette.
By click on of the Colormaps, other palettes may be selected:
Note: The selection of the Batlow palette represents a good compromise, in terms of the previously often traditional "rainbow colors" palette and the currently recommended.
To select the color palette for the residual field/”Residual Anomaly” select the tab “Residual Anomaly”:
The Vik palette is grouped around a central value (here: the Null value of the residual anomaly).
By click on of the Colormaps, other palettes can be selected.
Save project¶
At the end of each working phase, but also frequently during this process, it is advisable to save the model.
(1) This action is initiated by a click in the toolbar “SAVE PROJECT”.
A window will appear warning you not to overwrite the current model version. If this is desired, click
IGMAS+ will create a new Model INPUT. Loading a model file in the next working phase you see that in the Timeline appears the former model (in green colour) and the new model blue shaded:
If you click NO, nothing will happen and the model will remain. CANCEL will terminate the action without decision.
(2) There is a second possibility to save model changes.
Click on “File” in the TITLE BAR
In the pull down menu appears (short key is “Strg+S” bottom) and .
- “Save project” will save the entire model as already described above in (1).
- “Save as” enables the user to give a new name to the model output.
Click on the “create a new folder symbol” , and ...
rename the new folder and press “save”.
Export Results and Model components¶
IGMAS+ does not provide the user with direct tools for printing model components and fields (calculated, measured and residual fields). It is not necessarily the task of an interactive modeling software to offer all possibilities of a modern graphics processing. However, in order to take advantage of this, there are a number of possibilities for the user to further process IGMAS+ results with this other software.
Clicking FILE in the TITLE BAR select “Export” and get information on the components to export:
IGMAS+ offers seven Export actions:
- (1) Borehole(s),
- (2) Model,
- (3) Stations,
- (4) Interface(s),
- (5) Voxelcube,
- (6) Border-VoxelCube and
- (7) StressMap.
The exports are alpha-numeric and are used for further processing of the model results in external software.
(1) Borehole(s) (To be done)¶
(2) Model¶
After clicking this wizard appears on the screen.
Click: Save 
In the selected folder in your PC folder structure you will find the new file My model.model:
The file is opened with an editor and the entire model structure with the IGMAS+ geometry, the fields and other components can be seen in plain text:
Here we show snippets from the relatively large XML file:
(3) Stations¶
In contrast to the model export, we select [csv] [xyz] - Comma Separated Values, which can be used in many external computer programs for further processing.
Make sure that the units of the station data (here: meters), the acceleration/gravity (here: mGal), the gravity Gradient(s) and or the magnetic Field are specified correctly according to the modelling. In the separator field, "blank" (used in the example above) or a tabulator can be used.
Click: Save
… and above the progress bar (bottom right of the screen) you will read the information that the stations were successfully saved:
In the selected folder in your PC folder structure you will find the new file
My stations.model:
This file is much smaller than the saved “Model file” and looks like this:
"x" "y" "z" "measured z component" "calculated z component" "residual z component"
When continuing to process the station file externally, you should make sure that the software can process the header in the station file.
(4) Interface(s)¶
Select in the TITLE BAR Export > Exort > Interface(s)
and get the screen:
Check "the file "My Interfaces:
This ia large file (22 MB); here we prsent a short parge only to get information on its structure.
(5) Voxelcube¶
The saved Voxelcube always has the extension ".vxo". The file can be renamed without problems and get the extension ".txt" - then it can be read with any editor.. The file-header and the first lines of the file look like this:
(6) Border-Voxelcube¶
to be added
(7) Stress map (to be done)¶
Miscellaneous¶
Switch on and off fields¶
Refer to OBJECT TREE an select Fields. If you don't want any fields to be displayed at all, uncheck the box with the blue checkmark in front of Fields. If fields are to be displayed, then expand the tree under Fields, by clicking on . By unchecking the blue tick boxes in front of the corresponding fields (calc Gz or meas Gz or Residual Anomaly), the corresponding field can then be switched off/off respectively.
Point information of model parts¶
In addition to the Property Editor and Body Manager, there is also the Information Tab. Click on Information > move the mouse over the screen. The window now shows the information about the respective item.
IGMAS+ Shortcut table¶
