Compute distance

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Compute distance

Compute distance

Compute distance command computes a distance value for points. The distance can be computed based on several references:

3D vector elements in the CAD file, such as planar shapes, linear elements or surface elements.

the closest overlapping line in a point cloud.

the average between overlapping lines.

ground class(es) or other class(es).

any surface model loaded in TerraModeler.

powerline wires that have been produced with the Detect wires tool.

range which is the distance to the scanner position at the point of time when a point was captured. This requires trajectory information available in TerraScan.

built-in vegetation indexes Normalized and Visual band differences. This requires true-color (Visual band difference) and additionally infra-red color information (Normalized difference) stored for the points. The distance value expresses how likely a point belongs to vegetation (larger positive value) or not (larger negative value). Distance values range between -1 and +1. The vegetation index distance values may support the ground classification of photogrammetric point clouds.

road bumps and potholes represented by vector elements, such as lines or polygons.

The distance value can be used for visualization of points and for further processing steps. The following processing commands rely on a distance computed from ground:

Classify by distance / Classify groups by distance

Assign groups and corresponding macro action

Classify groups by best match

The distance value can be stored in TerraScan FastBinary files.

To compute distance values:

1. If you want to compute distance values for road bumps and potholes, select the vector elements that represent these road damages.

2. Select Compute distance command from the Tools pulldown menu.

This opens the Compute Distance dialog:

compute_distance_elements compute_distance_ground

2. Define settings and click OK.

This computes the distance values. An information dialog shows the number of effected points when the process is finished.

SETTING

EFFECT

Class

Point class(es) for which dimensions and normal vectors are computed.

_select_classes

Opens the Select classes dialog which contains the list of active classes in TerraScan. You can select multiple source classes from the list that are then used in the Class field.

Compare to

Method for computing the distance:

Elements - distance between a point and vector elements drawn in the CAD file.

Closest line 3D - 3D distance between a point and its closest neighbour point. The computation takes the normal vector direction of points into account.

Closest line dz - vertical distance between a point and its closest neighbour point in XY of another line.

Line average Z - vertical distance from a point to the average elevation between overlapping lines. The computation is based on TINs created from points of one line.

Ground class - vertical distance from a point to the ground class(es). A temporary TIN is created from points in the ground class(es) in order to compute the distance.

Another class - vertical distance from a point to points in the given Other class.

Wires - distance from a point to the closest powerline wire. Line strings for wires must be produced with the Detect wires tool.

<TIN> - distance from a point to a surface model loaded in TerraModeler.

Range 3D - 3D distance from the scanner position to a point.

Range xy - horizontal distance from the scanner position to a point.

Range offset - left/right distance from the scanner position to a point.

Range forward - forward/backward distance from the scanner position to a point.

Range dz - vertical distance from the scanner position to a point.

Normalized difference - built-in vegetation index.

Visual band difference - built-in vegetation index.

Road bumps & potholes - distance to road surface damages represented by vector elements.

Levels

Numbers of CAD file levels on which the elements are drawn. Level ranges and several levels can be define with minus and comma, for example: 1-5,10,22. This is only active if Compare to is set to Elements.

Max distance

Maximum distance of points from elements for which a distance value is computed. This is only active if Compare to is set to Elements.

Planar shapes

If on, planar shapes are considered as reference elements. This is only active if Compare to is set to Elements.

Tolerance

Defines a stroking tolerance for curved element types. This determines what shapes are considered as planar. This is only active if Compare to is set to Elements and Planar shapes is switched on.

Above is

Defines which direction is considered as positive distance from planar shapes:

Upwards - points above a shape.

Clockwise side - points in clockwise direction of a shape.

This is only active if Compare to is set to Elements and Planar shapes is switched on.

Linear elements

If on, linear elements are used for computing a distance. This is only active if Compare to is set to Elements.

Surface elements

If on, surface elements are used for computing a distance. This is only active if Compare to is set to Elements.

Max distance

Maximum distance between overlapping lines for which a distance value is computed. This is only active if Compare to is set to Closest line 3D or Closest line dz.

Ground

Point class(es) used as reference ground level. This is only active if Compare to is set to Ground class.

_select_classes

Opens the Select classes dialog which contains the list of active classes in TerraScan. You can select multiple source classes from the list that are then used in the Ground field. This is only active if Compare to is set to Ground class.

Other class

Point class(es) used as reference class(es). This is only active if Compare to is set to Another class.

_select_classes

Opens the Select classes dialog which contains the list of active classes in TerraScan. You can select multiple source classes from the list that are then used in the Other class field. This is only active if Compare to is set to Another class.

Max distance

Maximum distance between a point and reference points in another class. The distance value is not stored for a point if it is larger than the given maximum value. This is only active if Compare to is set to Another class.

Wire levels

Number(s) of CAD file level(s) on which powerline wires are drawn. Several level number can be separated by comma, a range of level numbers can be defined by a minus sign, for example 10,14,22 or 3-5. This is only active if Compare to is set to Wires.

Find using

Distance definition:

Vertical distance to wire - vertical distance from a wire.

3D distance to wire - 3D distance from a wire.

Falling tree logic - each point is considered as the tip of a tree with its trunk at the xy location of the point and the elevation of the base point on the ground. The shortest distance of the point “falling like a tree” to a wire is computed.

This is only active if Compare to is set to Wires.

Within offset

Maximum horizontal distance from a wire within which a distance value is computed. Basically, this value defines the corridor left and right of the wires for computing distance values. This is only active if Compare to is set to Wires.

Ground

Point class(es) used as ground level. This is only active if Compare to is set to Wires and Find using to Fallen tree logic.

Limit

Threshold value that separates vegetation from non-vegetation by using a vegetation index. This is only active if Compare to is set to Normalized difference or Visual band difference.

Max offset

Maximum horizontal distance of a point from the element that represents a bump or pothole. Only point within the given offset are considered in the distance computation. This is only active if Compare to is set to Road bumps & potholes.

Fit length

This is only active if Compare to is set to Road bumps & potholes.

Fit depth

This is only active if Compare to is set to Road bumps & potholes.