[GRASS-dev] Re: [GRASS-user] LiDAR LAS import

[Markus Metz]

On Wed, May 25, 2011 at 12:16 PM, Hamish <hamish_b at yahoo.com> wrote:
> Markus Metz wrote:
>> Hi all,
>>
>> GRASS 7 has a new module v.in.lidar for importing LiDAR LAS files
>> (*.las or *.laz). The LAS file format is commonly used for storing
>> LiDAR point clouds, but is unfortunately not supported by OGR.
>> v.in.lidar uses the libLAS library [0] and is only compiled if the
>> libLAS library is present.
>>
>> I chose to use the library instead of writing a custom LAS reading
>> interface because the current LAS library version 1.6.1 is stable,
>> supports LAS file versions 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, each of
>> which can store LiDAR points in up to 5 different point formats. The
>> user and the interface do not need to know the file version and point
>> format of a given file, all that is conveniently handled by the libLAS
>> library in the background. The library has Large File Support (LFS)
>> and is well tested on different platforms, also with different
>> endian-ness. This functionality is not that easy to replicate.
>>
>> You will need to get the libLAS library and configure GRASS 7 with
>> --with-liblas in order to have the module available. Please test!
>>
>> Markus M
>>
>> [0] http://www.liblas.org
>
>
> neat! any time trials to say how much faster it is than piping
>  las2txt | v.in.ascii
> ?

Note that las2txt does NOT apply scale and offset to x,y,z, this would
need to be done afterwards in order to obtain correct coordinates.
Therefore the output of las2txt | v.in.ascii with the sample las file
I used is incorrect.

I discovered a bug in v.in.ascii: from a point file with | as field
separator like

1|2|3||5|6

only the first 3 columns will be imported because column 4 is empty
which means that columns 5 and 6 are skipped.

v.in.lidar is a notch faster than las2txt | v.in.ascii. And easier to use...
Speed comparisons:

# sample las file with 1,287,775 points

# with table and topology
time las2txt -i points.las --stdout --parse xyztinrcCpedRGBau
--delimiter "|" | v.in.ascii in=- out=points_ascii -z x=1 y=2 z=3 --o

real	6m34.430s
user	4m57.530s
sys	2m3.693s

time v.in.lidar in=points.las out=points_las -o --o

real	6m13.823s
user	4m32.061s
sys	2m1.068s


# without table, with topology
time las2txt -i points.las --stdout --parse xyz --delimiter "|" |
v.in.ascii in=- out=points_ascii -zt x=1 y=2 z=3 --o

real	1m53.578s
user	1m47.032s
sys	0m9.238s

time v.in.lidar in=points.las out=points_las -ot --o

real	1m44.876s
user	1m34.450s
sys	0m8.488s