[pgpointcloud] Overlapping patches

[Nilesh Vyavahare]

Hi Paul,

Thanks for your reply. I have added further comments below.

Nilesh

From: Paul Ramsey [mailto:pramsey at cleverelephant.ca]
Sent: Thursday, January 30, 2014 3:48 PM
To: Nilesh Vyavahare; pgpointcloud at lists.osgeo.org
Subject: Re: [pgpointcloud] Overlapping patches

On January 30, 2014 at 5:12:51 AM, Nilesh Vyavahare (nilesh.vyavahare at seazone.com<mailto://nilesh.vyavahare@seazone.com>) wrote:
Hello everyone,
1) I am using PDAL pcpipeline to upload some data into Postgres. In the pcpipeline I have specified to split the data into the patches of 400 points. From the demonstration example I understand that the patches will not be overlapping but when I look at the extents of patches (and the points themselves) they appear to be overlapping. I have attached the pipeline xml I am using. Am I missing some trick here?

I’ll wait for Howard to answer this one, but even if the patches are not perfectly non-overlapping that’s not the end of the world, pgpointcloud really doesn’t care either way, and patches that are “mostly not overlapping” will be just as efficient as ones “totally not overlapping"

The amount of overlap I am getting between patches is usually more than 90%. The reason I am more after non-overlapping patches is because I am thinking of first comparing patch extents with a geometry to work out intersecting points, which hopefully should reduce time to work out intersecting points with a geometry. Or do you think it takes about the same time to work out the intersection either you compare patch extent or patch itself?
2) Another thing I was wondering is that, in PDAL you have one filter called “filters.hexabin” which is supposed draw an outline around the patch. At the moment the only way I could get the patch extent out, is to write out an xml file. Is there any way to write that extent into PostGIS directly next to the patch?

You can get the extent of the patch just by casting it to geometry.  To experience, just

select st_astext(mypatch::geometry) from mytable;

Now, it may be that I made the wrong choice in that cast and it should create a multi-point, but I’m sticking with it for now. Folks who want points can also explode their patches first. Casting a pcpoint to geometry returns a pointz.

Thanks for this Paul. I am probably being bit more demanding but the extent given by this way is an MBR, can I get hexbin extent in pgpointcloud similar to the ones shown in Howard’s PDAL hexbin filters?

P.






Just a note, in case you are specifying pre_sql/post_sql inside your pipeline, specifying the SQL statement inside the pipeline xml file didn’t work for me so I had to write SQL statement in some other file and put the location of that sql file in there and it worked.

Thanks in advance for your help.

Regards,
Nilesh

Nilesh Vyavahare
Senior GIS Analyst, SeaZone

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- Pipeline_Template.xml, 4 KB
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