Create Isoshells - Volume

To access this screen:

Define a bounding box within which isoshells are calculated. This provides the advantages of restricting the volume to a specific area of interest, and minimizing the effects of extrapolation.

  • Horizontal extents are defined by the intersection of the Inside perimeter and Inside wireframe hulls, if defined. If these files have not been specified, the horizontal extent of the input sample file is used instead.
  • The maximum vertical extent is defined by the lowest maximum elevations of the Below wireframe or Inside wireframe hulls, if defined.  If these files have not been specified, the maximum vertical extent of the input sample file is used instead.
  • The minimum vertical extent is defined by the highest minimum elevation of the Above wireframe or Inside wireframe hulls, if defined. If these files have not been specified, the minimum vertical extent of the input sample file is used instead.
  • If Align with search ellipse is selected in the Alignment group, then the bounding box is extended to enable the values specified for Below wireframe, Above wireframe, Inside Wireframe and Inside perimeter to be processed in world space. This means that ‘above’ and ‘below’ are always relative to the world vertical axis, regardless of any dip in the search ellipse.

Bounding Box Guidelines

  • Horizontal extents are defined by the intersection of the Inside perimeter and Inside wireframe hulls, if defined. If these files have not been specified, the horizontal extent of the input sample file is used instead.
  • The maximum vertical extent is defined by the lowest maximum elevations of the Below wireframe or Inside wireframe hulls, if defined.  If these files have not been specified, the maximum vertical extent of the input sample file is used instead.
  • The minimum vertical extent is defined by the highest minimum elevation of the Above wireframe or Inside wireframe hulls, if defined. If these files have not been specified, the minimum vertical extent of the input sample file is used instead.
  • If Align with search ellipse is checked, the bounding box is extended to enable the Below wireframe, Above wireframe, and perimeters to be processed in world space. This means that ‘above’ and ‘below’ are always relative to the world vertical axis, regardless of any dip in the search ellipse.

Tip: reinstate the values used in the last successful isoshells run using Restore.

To constrain the generation of isoshells within a defined cuboid:

  1. Decide if the grid of interpolated points and the bounding box are to be aligned with the defined search ellipse (see Create Isoshells - Estimation Parameters):

    • If Alignment is checked, points and hull are aligned with the search volume.

      Note: for an anisotropic search volume, the structure is probably orientated similarly. As such, the grid of interpolated points and the bounding box are, by default, aligned with the search ellipse volume.

    • If Alignment is unchecked, points and hull are aligned with the world axes.

  2. Optionally, further restrict the area within the bounding box by specifying additional reference data in the form of Boundaries:

    • Inside perimeter—restrict the horizontal extents of the isoshells using a perimeter string - this could be an external file (use the browse button), or could be selected previously in any 3D window, using the Selected in view option. With this option, you can't select 3D data whilst the Create Isoshells screen is displayed. To select data:

      1. click Cancel.

      2. Select string data in any 3D window.

      3. Redisplay the Create Isoshells screen.

      4. Click Restore.

      5. Return to the Volume tab and continue entering parameters.

      Note: if more than one perimeter is in the file or selection, the valid region is defined as within any perimeter.

    • Below wireframe—specify the maximum elevation of isoshells relative to a DTM wireframe, for example, a topography. Another example is a DTM surface which is created from the coordinates of the top mineralized sample in each drillhole. Select this option and pick a wireframe using the Project Browser.

    • Below or Above wireframe—specify the minimum elevation of isoshells relative to a DTM wireframe, for example, a DTM surface created from the coordinates of the bottom mineralized sample in each drillhole.

    • Inside wireframe—confine isoshells to within a closed wireframe.

  3. Define a Bounding Box if you want to constrain results to a specified 3D cuboid.

    To define boundary box constraints:

    1. Choose if you wish to create a constraining cuboid automatically:

      • If Fit to data and boundaries is checked, a bounding box is automatically set using the hulls of the sample file and bounding data.

      • If Fit to data and boundaries is unchecked, you can define a bounding box manually. In this case, the bounding box must not extend significantly from the original samples: isoshells generated from extrapolated values will be significantly less valid than those formed from interpolated values between samples.

        If manual selection is chosen, the fields in this section become active. What they are called depends on whether you are automatically aligning data with the defined search ellipse:

        • If Align with search ellipse is checked, values are displayed in world coordinates using Origin and Lengths fields.

        • If Align with search ellipse is unchecked, world coordinates are shown using Minimum and Maximum fields. An error message is displayed if an invalid bounding box is entered (maximum values less than or equal to minimum values, or length values less than or equal to '0').

          If Align with search ellipse is unchecked and Fit to data and boundaries is also unchecked, the bounding box is automatically set to a minimum of '0', and a maximum of '1' for X, Y and Z, and appropriate minimum and maximum values must be manually specified.

        Note: although isoshells output is constrained by these parameters, it will not necessarily fit them precisely: the closeness of fit is determined by the coarseness of the Triangle Spacing parameter defined on the Output tab.

Related topics and activities