ModelVision KB

How can I compute the Magnetic Field of a project area? 

To compute the Magnetic Field (i.e. Total Intensity, Inclination and Declination) you must know the Latitude and Longitude of the project area.

Access the Project Properties dialog from the File>Project Properties menu option and select the IGRF button on the right-hand side of the dialog. Choose a localised map from the drop-down list in the IGRF dialog that appears and click on the map in the area of the project.

Alternatively enter the
Latitude/Longitude/Altitude of the project area and click OK. The Magnetic Field is then automatically calculated.

How can I determine the volume of a modelled body?

The volume of a created tabular or polygonal body in ModelVision is automatically calculated during the modelling process. The resultant value can be viewed in the Body Properties dialog.

To access the Body Properties dialog double-click the left mouse button on the target body in any view. Alternatively view the Body Table (accessed from the Model>Body Operations menu option) and double-click with the left mouse button on the row header cell of the target body.

How can I show my drillholes in a cross-section view?

To show either synthetic or imported drillholes in a cross-section view access the Cross-section Layer Table by clicking on the Layer Table toolbar button or right mouse button within the active cross-section window and choose the Configure Layers option from the pop-up menu. Then right click on the Cross-section Layers table to select Add>Drillhole. Move the drillholes that you wish to display to the Selected list on the right-hand side of the Drillhole Selection dialog. Click OK to return to the cross-section view to see the added drillholes.

How do I not display the Flight Lines or Base Lines in a 2D Map?

Turn off the display of survey database flight lines or base lines from the Map Layers Table.  Access this by clicking on the Layer Table toolbar button or right mouse button within the active map and select the Configure Layers option from the pop-up menu. In the Map Layers Table deselect the tick boxes for Baselines and /or Flight Lines. 

How can I set the background density or susceptibility?

The default background density and susceptibility values are set to 2.65 (mgal) and 0.0000 (cgs) respectively but can be changed by accessing the Model Parameters dialog from the Project Properties dialog, which is accessed from the File>Project Properties menu option. In the Project Properties dialog select the Model button on the left-hand side to display the Model Parameters dialog.

The Model Parameters dialog can also be accessed from the Model>Model Parameters menu option.
The default modelled density and susceptibility values are also defined in this dialog and are set to 2.77 (mgal) and 0.001 (cgs) respectively.

How can I set the default units for density and susceptibility?

The default density and susceptibility units are set to mgal and cgs by default.  These units can be changed by accessing the Project Properties dialog from the File>Project Properties menu option and changing the units for Mag Units and Grav Units

How can I produce a spreadsheet of my modelled bodies and their properties? 

You can view a spreadsheet of the modelled bodies and their associated properties by selecting the File>Export>CSV Format menu option.

How can I load a DXF file into ModelVision?

Any external DXF or TKM (ModelVision format) file for a model can be imported into ModelVision by using the Model>Import menu option.

When importing a DXF file, the ModelVision Topology Checker dialog will appear, providing a preview of the model and checking the integrity of the model. If any unclosed edges, etc are detected these are reported and not imported. 

How can I improve the speed of modelling in my session?

The speed at which ModelVision can model magnetic or gravity anomalies depends upon how many data points are being used in the session. Therefore, to increase the modelling efficiency of the software, it is advisable to isolate the area that is being modelled. 

Use the Clip Project toolbar button to drag out a rectangular polygon of the area that you wish to clip to and click OK on the confirm dialog that appears. Note: once the data has been clipped you will not be able to display the full dataset again in the current session. Therefore, it is advisable to save the session for future use prior to clipping the project.

Can I use ModelVision for applying terrain corrections to gravity data?

ModelVision has the capability to compute terrain corrections for zones of different density, assigned according to a geological map. This is performed by using the 3D Model Generator utility.

Therefore, if you want to model data using ModelVision, you do not need any processing software to apply terrain corrections to the data beforehand. Just use the 3D Model Generator to apply a terrain grid surface as the primary surface and the input data can be from an imported vector file detailing zonal properties (X, Y,Z and density).

Note: If you are only looking to PROCESS gravity data, ModelVision may not be the optimum choice of software. If however, you then want to proceed to model the data, ModelVision is the foremost software package you can use. ModelVision is used by many leading mineral exploration companies as their primary software for modelling gravity and magnetic data.

How is the Koenigsberger (Q) ratio and NRM-intensity calculated in ModelVision?

The Koenigsberger ratio Q is the ratio of the remanent magnetization to the induced magnetization.  Using the abbreviations in the Body Properties dialog the formula is:

NRM Intensity/Jind

The susceptibility is in SI units but in version 12.0 and earlier, the magnetization units are in gamma rather than A/m (as expected for SI).  This was changed to SI in version 13.0. This can be tested by changing the calculation mode to CGS units in the File>Project Properties dialog.

How do I import and display ModelVison .TKM files in Discover PA?

There are two options:

a)    TKM files can be handled as 3D .EGB images. They can therefore be displayed either by opening from
       within an Image branch, or by dragging and dropping directly into the Discover 3D window.
b)    Alternatively, import your .TKM file into a Feature Database (Features>Import). This will also allow the
       import of any attributes if imported into a new feature database, using the TKM file's fields as a template. 

What is the gravity modelling technique in ModelVision when using the background density?

In ModelVision, the amplitude of the gravity or magnetic anomaly of a body is proportional to the difference between its property (density or magnetic susceptibility) and the background (density or magnetic susceptibility). If a body has the same property as background, then it will generate no anomaly.

With magnetic modelling we almost always set the background susceptibility to 0 and consider the absolute susceptibility values of targets. With gravity you can generally choose a background density value.

If you want to model free air data and include terrain in the model, the background density must be 0, with true densities for the rocks. If you are modelling Bouguer data then you can choose your background density. If for instance you are modelling variation in thickness of overburden on bedrock, by setting the background density to represent the bedrock, you only need a body for the overburden.

In a case of three distinct densities (representing kimberlite, limestone and granite), if your granite/limestone interface is very extensive and flat then it will generate no change in gravity. Therefore, you can make one body for the kimberlite intruding limestone, and a second body beneath it for the kimberlite intruding granite. If you set the background density to 0 then the first body would have a density of (kimberlite – limestone) and the deeper body would have a density of (kimberlite – granite). You will not need bodies for the granite or the limestone.

Assume (values are nominal only) limestone = 2.9 gm/cc, granite = 2.65, kimberlite = 2.4. Then set background density to zero and have one body of “kimberlite in limestone” with density = 2.4-2.9 = -0.5 gm/cc, and beneath it “kimberlite in granite” with density = 2.4-2.65 = -0.25 gm/cc.

However, where the geometry is more complicated and you must include gravity variations caused by the geometry of the limestone/granite interface, you may need to overlap bodies. In this case, each volume of a body overlap has an effective density contrast given by the sum of the contrast of each of the overlapping bodies against background. In the case of having overlapping bodies it is most convenient (but not necessary) to have the background density = 0.

For example, referencing the above densities, follow the steps below:
  1. set background density = 0 and let this represent the granite (true density 2.65). You do not need any granite body.
  2. A block of limestone by itself has a density of (2.9-2.65 = 0.25 gm/cc).
  3. The kimberlite intruding the granite has a density of (2.4-2.65 = -0.25 gm/cc).
  4. The kimberlite intruding the limestone also needs a contrast of -0.25 gm/cc, but if you are using a body for the limestone then the volume occupied by the kimberlite intruded into it already has a contrast of +0.25 gm/cc. You therefore need to give the “kimberlite in limestone” body a density of -0.5 gm/cc to take that contrast from +0.25 to -0.25.
Obviously, try to avoid the need to overlap bodies, although this is not always possible.