Distance Functions

A distance function calculates the distance to a selected set of data objects. This topic describes how to create and modify distance functions. It is divided into:

To create a distance function, right-click on the Numeric Models folder and select New Distance Function. The New Distance Function window will be displayed.

If you are unsure of some settings, most can be changed later. For a basic distance function click Select Objects to select from the suitable objects available in the project, then click on the Buffers tab to define at least one buffer so that the distance function can be visualised in the scene.

Click OK to create the distance function, which will be added to the Numeric Models folder. The new distance function contains objects representing different parts of the function, which can be expanded to show the inputs to each part of the function:

  • The Trend object that describes the trend applied.
  • Hyperlinks to objects used for the distance function.
  • An Isosurfaces folder that contains all the meshes generated in building the distance function. In this example, two isosurfaces have been defined, at distances 2 and 4.
  • An Output Volumes folder that contains all the distance buffer meshes.

Other objects may appear in the project tree under the function as you make changes to it.

Display the function by dragging it into the scene or by right-clicking on it and selecting View Buffers.

Once you have created a distance function, you can adjust its properties by double-clicking on it. You can also double-click on the individual objects that make up the function.

Selecting and Filtering Data Objects

Click Select Objects to choose from the objects available in the project. For drilling data and points data, you can apply any filter that has been defined for that object. For example, here:

  • A query filter has been selected for the collar table
  • Query filters are available for the assay table, but none have been selected
  • No query filters have been defined for the points data object

If there is no Query Filter option shown for a data object, that is because it is not possible to filter the data used for the distance function for that type of object, as is the case for the GIS line shown above.

Options for Closed Surfaces

If any of the objects selected are closed surfaces, you can choose whether these surfaces are treated as Volumes or as Surfaces.

  • When treated as Volumes, buffers will be generated only on the outside of the object. If the object is inverted, buffers will appear on its inner surface.
  • When treated as Surfaces, buffers will be generated on both sides of the object.

In the examples that follow, a distance function is created from a sphere and a single isosurface is defined in the Buffers tab, with its distance set to 2:

The sphere used as the basis for the distance function is coloured red on the inside and blue on the outside.

Treat Closed Surfaces as Volumes

When a surface is treated as a volume, isosurfaces are generated on the outside (the blue side) of the surface. In this example, a single isosurface (in yellow) is generated a distance of 2 away from the blue side of the sphere:

Here the orientation of the sphere has been reversed; the blue (outer) side faces inward and the red (inner) side faces outward. The isosurface (yellow) is, again, generated the specified distance of 2 from the blue side of the sphere:

Treat Closed Surfaces as Surfaces

When the sphere is treated as a surface rather than as a volume, isosurfaces are generated on both sides of the sphere:

When the orientation of the sphere is reversed, there is no difference in the isosurfaces generated:

Setting the Boundary

In the Boundary tab, you can set whether the function boundary is clipped or unclipped. No distance buffer clipping is the default setting, but if you choose to clip the buffers, you can choose between:

  • Sharing another object’s extents
  • Defining a set of extents that is independent of other objects in the project.

When you select the Shared with option, the distance function will be updated when the extents object it shares is updated.

Setting a Trend

In the Trend tab, you can set a trend using the moving plane or by entering the required values. You can also use the Set to list to choose different options used in the project. Isotropic is the default option used when the function is created.

The Ellipsoid Ratios determine the relative shape and strength of the ellipsoids in the scene, where:

  • The Maximum value is the relative strength in the direction of the green line on the moving plane.
  • The Intermed. value is the relative strength in the direction perpendicular to the green line on the moving plane.
  • The Minimum value is the relative strength in the direction orthogonal to the plane.

Adding Buffers

To add buffers, click on the Buffers tab, then click the Add button ():

Enter the required value. To delete a buffer, click on it in the list, then click the Remove button (). You can also change the colours used to display the buffers by clicking on the colour chips. The Default resolution setting is used for all new buffers and for existing buffers that use the default resolution.

There are two options for Volume Type that affect how the buffers are calculated when more than one buffer is used. The Concentric option produces volumes that include any lower distance volumes. For example, here there are three volumes, <2, <4 and <6, and the colours used to display these volumes blend where the volumes overlap:

The Intervals option produces discrete, non-intersecting volumes. In this example, there is no overlap between the <2, 2-4 and 4-6 volumes: