Import
Import 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.
???+ note 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`](https://surferhelp.goldensoftware.com/subsys/subsys_geosoft_grid_file_descr.htm). The `*.csv` file format is preferred.
**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).???+ warning 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.
Choose ++"File"++ --> ++"New Project"++ --> ++"Irregular/Regular Horizon (XY-Plane) Import"++ -> ++"Finish"++:
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.
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.
???+ note "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… 
Load a project
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](./appearance.md#theme).