Point cloud classification

Apply to Classes: the source classes which will be reassigned to a new class

To Class: the target class to assign

Apply to Classes: the source classes which will be reassigned to a new class

To Class: the target class to assign

AOI: file containing the polygons to be used. Points from Apply to Classes which intersect the polygon in 2D (horizontal) space will be assigned to the To Class. Multiple polygon layers may be configured in a single classification run

Buffer Distance: buffer to apply to polygons

Polygons on different layers should not overlap each other, otherwise the classifier may give unexpected results for the Destination class of intersecting points.

Apply to Classes: the source classes which will be reassigned to the Ground Class (class 2)

Max Building size (m): maximum side length of a building in the input data

The max building should be larger than the max diagonal length of the largest building in the area so that the classifier does not mistakenly choose the building points as ground seed points, which eventually causes parts of the large building to be classified as the ground.

For dense vegetation and rugged terrain area, you may lower the max building size. It can help to select more ground seed points and will help to get more details of the true terrain model

Iteration angle (degrees) and Iteration distance (m):
Per cache tile, the classification process will identify initial ground points in a window corresponding to the max. building size by looking for the lowest available point. These key points are used to build a TIN representing the initial ground surface. To further densify the TIN, point candidates falling into a triangle are evaluated,

• whether they deviate less than the given iteration angle from the initial triangle and

• whether the new key point has a Z distance less than the iteration distance from the initial triangle

If so, this point is added to the ground class.

This parameter is critical to classify different terrain types. For rugged terrain, increase the iteration angle. This will help to approximate the high relief terrain better, but most likely may also classify some low vegetation points mistakenly.

To avoid low vegetation in such scenarios, it is recommended to decrease the iteration distance alongside.

Max Terrain Slope (degrees): max. allowed slope angle in TIN, will be used to avoid high slope triangles

Offset: Vertical offset to classify the points close to ground surface to ground points in the final iteration

Point Processing Options

Use current ground points: if enabled, already existing ground points (e.g. from a previous classification) are used as key points to identify additional ground points

Reduced iteration: If enabled, the refinement of the triangles will be less aggressive.  Once the max. triangle length of a given triangle is below the given distance specified via the “Reduced Iteration” setting, the iteration angle will be reduced proportional for further iterations.

Stop iteration: If enabled, the refinement of triangles will stop, as soon the max. triangle length of a given triangle is below the iteration threshold

Options “Reduced Iteration“ & “Stop Iteration“ may be used like a Thinning tool when dealing with quite dense point clouds

Use all/ last/ first return: specify the type of returns to be used in the classification process. (Default = all)

Cache Size: the size of the tile to be processed in meters. Each tile will be processed as one unit in memory. The memory required for a tile is a function of the cache size and the point density of the input point cloud. Cache size may need to be reduced if there is not enough memory available.

Cache Buffer Size: when Ground Classification is applied set to one-half the building size parameter used. Otherwise a value of 50 meters will serve for most cases.