[postgis-users] Point cloud questions (PC NEWBIE here)

[Newcomb, Doug]

Bob,
I've had a fair amount of success directly generating rasters from the z
values  from LAS files of 3.3 billion points each using GRASS7 complied
with liblas and the r.in.lidar,
http://grass.osgeo.org/grass70/manuals/r.in.lidar.html command.

As Remi mentioned, it can be quite memory intensive,
http://www.ncgisconference.com/2013/documents/pdfs/Newcomb_Fri_1030.pdf .
Point counts and Range calculations are fairly cheap, but skewness analysis
can take a LOT of memory.  For the 3.3 billion point data sets on partial
coverage of a 753 million cell raster and limiting the amount of map in
memory that was processed at one time to 15%, it still took 20GB of RAM  to
process for a skewness analysis.  The extent of the raster created was much
larger than the area covered by points, so that probably made some
difference.  Only processing an area for which there are points might cut
down on the memory requirements somewhat.

Doug




On Mon, Oct 21, 2013 at 4:52 AM, Rémi Cura <remi.cura at gmail.com> wrote:

> Hey,
> I'm not M.Ramsey,  I'm just a pointcloud user.
>
> 1. : you can "colorize" based on any attributes of points. Traditional
> point cloud softwares expect usually R G B attributes, but for some you can
> choose which attributes to use for coloring (CloudCompare).
>
> 2 : We have thought about visualisation (in this area it's about Level Of
> Details). The best we tried (because of lack of time) is to make another
> PC_Explode so it returns only a certain number of points per patch.
>
> The next step is to writte points in patch following a quad tree structure
> (not deep first but breadth-first) (maybe using
> http://www.postgresql.org/docs/9.3/static/spgist-examples.html , not sure
> about this).
> This way when taking only the first XX points in patches, you ensure these
> points are always well distributed in the patch.
>
> This is the best we thought of without duplicating data (not an option
> with so big data anyway).
>
> 3 : about générating a raster from pointcloud :
> You can do it in QGis , Grass Gis, or using GDAL or LasTool. (also in
> CloudCompare) Usually you have access to sophisticated interpolation
> methods (square inverse distance, etc etc). It is a hard problem in
> practice because of memory limitation and possible multiple holes in data.
>
>
> Please feel free to ask if you want more details.
>
> Cheers,
>
> Rémi-C
>
>
>
>
> 2013/10/18 Basques, Bob (CI-StPaul) <bob.basques at ci.stpaul.mn.us>
>
>>  Hi all,****
>>
>> ** **
>>
>> Juat watched Paul Ramseys video on point cloud storage and it made me
>> think of a few questions to ask.****
>>
>> ** **
>>
>> Quesitions:****
>>
>> **·          **Sort of a DB processing question, probably not thought
>> about yet, but can the pointcloud be colorized based on a raster/vector of
>> view passed in?  As in aerial photos obviously, but less obvious would be
>> for oblique photos.  ****
>>
>> **·          **Generalizing of the pointclouds, from my perspective to
>> be used for zoom in/out processes for visualization.  Could a average
>> height based on a (pyramid) tiling possibly be used to get close to a
>> generalizing scheme, I know this approach might offend purists as far as
>> data integrity . .****
>>
>> **·          **There was a question in the video that I watched related
>> to building a surface grid from the pointcloud, I wonder about a simple
>> tile averaging as a method for generating a grid.  Anyone tried and have
>> available some benchmarks for this idea?****
>>
>> ** **
>>
>> Thanks****
>>
>> ** **
>>
>> Bobb****
>>
>> ** **
>>
>> ** **
>>
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>>
>
>
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-- 
Doug Newcomb
USFWS
Raleigh, NC
919-856-4520 ext. 14 doug_newcomb at fws.gov
---------------------------------------------------------------------------------------------------------
The opinions I express are my own and are not representative of the
official policy of the U.S.Fish and Wildlife Service or Dept. of the
Interior.   Life is too short for undocumented, proprietary data formats.
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