<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:verdana,helvetica,sans-serif;font-size:10pt"><div>Hamish wrote<br>>if you don't like the gridding aspect of it, and the lat/lon for<br>>all 4 retuns is identical, a small python or awk script could do<br>>the pre-processing for you in a simple and clear way.<br><br>Just to add my experience - I use awk to get a handle on the lidar xyz files (number of points, min, max, outliers etc) and filter for return (or scan angle etc) before importing into GRASS or any other software for that matter. Works like a dream and much faster than importing through software for the same information.<br><br>Carlos, if you want any pointers just let me know (though I am sure you're probably much more experienced than a noobie like me!)<br><br>Cheers,<br>Rebecca<br>Post-graduate Researcher<br>Bournemouth University, UK<br></div><div style="font-family:
verdana,helvetica,sans-serif; font-size: 10pt;"><br><div style="font-family: arial,helvetica,sans-serif; font-size: 13px;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Hamish <hamish_b@yahoo.com><br><b><span style="font-weight: bold;">To:</span></b> Carlos Grohmann <carlos.grohmann@gmail.com>; Markus Metz <markus.metz.giswork@googlemail.com><br><b><span style="font-weight: bold;">Cc:</span></b> GRASS user list <grass-user@lists.osgeo.org><br><b><span style="font-weight: bold;">Sent:</span></b> Sun, 30 January, 2011 22:08:00<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [GRASS-user] LiDAR interpolation (v.surf.bspline)<br></font><br>Carlos Grohmann wrote:<br>> > Also, the wiki page and man pages for v.lidar.* cite<br>> > examples of lidar data with two returns. How well should<br>> > the commands run with 4 returns? Any big changes in th<br>>
> procedure explained in the wiki?<br>Markus M:<br>> It is possible that the lidar toolchain does not work with<br>> 4 return because it classifies points into first or last<br>> return, nothing in between. In theory, it would suffice to<br>> identify the first and the last return, independent of the<br>> number of returns, in order to get a DSM and a DTM. The lidar<br>> filtering toolchain should work if you could remove 2. and 3.<br>> returns first.<br><br>set the resolution fine enough and r.in.xyz will allow you to<br>deal with the 4 returns any way you like.<br><br>if you don't like the gridding aspect of it, and the lat/lon for<br>all 4 retuns is identical, a small python or awk script could do<br>the pre-processing for you in a simple and clear way. maybe you<br>have to pipe it through `sort -n` first (but hopefully not).<br><br><br>Hamish<br><br><br><br>
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