Exlpanations on bulge and offset parameters

[Luca Pizzimenti]

Good morning,

I'm Luca Pizzimenti.

I need to understand how bulge and offset work and if these parameters work together in the ground surface estimation and how they influence each other. Can I have additional explanations?

thanks

Luca

[Martin Isenburg]

Hello Luca,

good observation ... the bulge and the offset parameters work somewhat together.

http://rapidlasso.com/lasground

http://lastools.org/download/lasground_README.txt

http://lastools.org/download/lasground_new_README.txt

The bulge and the offset parameters are used during the iterative TIN densification part of the lasground algorithm.

The bulge affects how the triangle that the point under consideration falls into is interpolated at this points x/y coordinate to compute its z_int. A bulge of zero means that the facet is planar and z_int lies "in the triangle". A bulge of non-zero means that the three normals of the triangles are used to "bulge" the triangle either up or down (depending on the normal direction) so that z_int can lie "above" or "below" the triangle.

The offset decides how high the real z of the considered point is allowed to lie above the interpolated z_int to be considered a ground point, namely no more than the offset. For an offset of zero, the real z of the considered point must be equal or lower than the interpolated z_int to become part of the ground. For an offset of 0.05, the real z of the considered point is allowed to lie up to 5 cm above the interpolated z_int to become part of the ground.

The offset parameter is also used at the very end of the ground finding. Essentially all points that are only a vertical distance of "offset" from the surface of Delaunay triangulated ground points are included into the ground in a final pass.

Regards,

Martin @rapidlasso

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