Adding Dimensions to Points

The Dimension options allow you to add dimensions to selected points.  The dimensions that are calculated relate to the reference model, and when these options are selected, you will be asked to select this model using the normal DTM selection dialog.  The dialog items in the Parameters group of this dialog will vary depending on the chosen option and will be described below.

These options all follow the current pick mode, so you will be asked to either indicate points, sketch a rectangle, or to confirm a list operation.

Heights 

The first two Dimension options, Interpolate and Ht Difference, will interpolate a height from the reference DTM and use this to create a dimension.  The name of that dimension is defined by the Dimension field in the dialog used to select the DTM.  When using a triangular DTM, the Group Depths checkbox can be used to adjust the interpolated height.  If this is checked and the picked triangle is part of a group, the interpolated height will be reduced by the group depth.  No dimension will be assigned if a triangle cannot be picked from the reference DTM.  Note that if a point is coincident with a point in the reference model and the triangles using that point have different groups assigned, the first triangle that is encountered will be used.

The Interpolate option allows you to store the interpolated height as a dimension.  The Ht Difference option will store the difference in height between the indicated point and the interpolated value.  Therefore, for this option to work, you will only be allowed to choose points that have a valid height.

Gradients and Directions

The Dimension Gradient & Direction option calculates gradient and direction automatically from the reference DTM. You can’t change the names: the gradient will always be labeled G=, and the direction will use the same label as the angle dimension (usually A=).

The gradient is shown as a percentage, while the direction is given in decimal degrees. Direction is measured as an angle starting from the positive x-axis (0°) and increasing in an anti-clockwise direction.

If a point lies on the edge between two DTM triangles, the software will use the first triangle it finds.

Perpendicular Offsets

Use this option when you need to calculate the perpendicular offset distance of a point to a DTM surface. The values will be added to the points dimensions box. 

A use case for this option would be for landfill sites, where you would need to know the thickness of a clay liner over the ground to ensure its effectiveness in sealing the ground below it and preventing chemicals from seeping into the groundwater.