[GRASS-dev] lidar tools update in grass7

[Markus Metz]

Soeren Gebbert wrote:
> Hello,
>
>>> A while back I did some crude profiling of the v.lidar tools and found
>>> that it was spending lots and lots of time in the Tcholetsky decomposition
>>> loop (3-for loops deep).
>>>
>>
>> That's better now because the matrix is a bit smaller.
>
> Yes, its a nice symmetric band matrix. Was a bit puzzling for me to
> understand the creation of the matrix without any documentation!

I added documentation where I understood the code but honestly, the
inner workins of the lidar_lib are still a mystery to me.

> So, i have implemented some conversion functions into the gmath
> library while moving the tchol* code from lidar lib into the gmath
> lib

There are still bugs in the code, mostly minor concerning warning and
error messages, one major in v.surf.bspline for very large raster
output regions. I'm busy fixing it, also converting it to a new module
r.resamp.bspline that does particularly well for filling NULL cells, a
real alternative to (the much slower) r.fillnulls.

>[...] i would suggest to use MPI parallelization or something else on
> process base, to concurrently compute the subregions which are created
> by default. Maybe a python script using overlapping tiling and
> subprocess  can do the job?

I think that should be integrated into the current lidar tools because
they make use of the current subregion tiling and C code is still
faster than Python code (right?). Treatment of overlapping zones of
neighbouring subregions is done sometimes in the lidar_lib, sometimes
by the modules themselves. It took me quite some time to understand it
and fix it, therefore I would advise against code porting/duplication.

My 2c,

Markus M