WARNING ... using brute_locate

[mauro...@gmail.com]

Hello,

does anybody know what this warning Message means? I couldn`t find any documentation on this. I get it if I`m trying to apply the spike free Algorithm of las2dem to some laz files.
For some time the algorithm continues working, but after a wile it stops. I just reacently manged to crash lastools this way.

Thanks,


Mauro

[Martin Isenburg]

Hello Mauro,

this WARNING has to do with the fact that the usual "point location" (e.g. walking the Delaunay triangulation) has failed and that the algorithm resorts to a "brute force" search over all triangles to find the right place where to insert the next LiDAR point into the TIN. In order to see what is going on exactly you would need to provide me with a link to those LiDAR files where this happens (preferably LASzip compressed LAZ files).

Regards,

Martin @rapidlasso 

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[Lee Stamm]

Hi,

Has this issue been resolved?

I have the same warning when generating a spike free CHM. 

I am attempting to do this for 149, 1Km tiles with density of 4-5 pts per sqm (last return) and it is very slow (compared to not using the spike_free) and there are many "WARNING....using brute_locate"messages for each tile which im sure i wasnt getting when using las2dem without spike_free algorithm.

Should i be worried about the brute locate- the CHMs coming out the other end look fine, 

Also, 

I will retile to 500m to see if it makes this faster. 

Cheers

Lee Stamm

[Martin Isenburg]

Hello Lee,

under the "hood" the spike-free CHM algorithm attempts to insert the LiDAR returns from top to bottom into the TIN that has more and more "frozen" triangles which corresponds to constraints in the Delaunay triangulation. To locate the next vertex on usually "walks" from the last triangle that was active to the new location. That is also why first sorting your LiDAR points into a z-order with

lassort -i chm_points.laz -odix _sorted -olaz

will speed up the running time of the spike-free CHM algorithm. Due to the many contraints in the spike-free TIN this "walk" sometimes fails. Then the algorithm simply loops over all triangles in the TIN to find the one that contains the vertex in question. Each time a WARNING is emitted because this is slow and should not happen too often.

The resulting spike-free CHM does not get affected by these WARNINGs. No surprise it looks fine. It just took a little longer to generate it.

Regards,

Martin @rapidlasso