<p>I need to calculate the number of points at different height levels. That is, how many points are from 0 to 5 meters? And from 5 to 10? And so on. So I believe I need to work with vector points and a database. Or is there another way?<br>
Thanks<br>
Daniel</p>
<div class="gmail_quote">On Mar 30, 2012 6:47 AM, "Daniel Lee" <<a href="mailto:lee@isi-solutions.org">lee@isi-solutions.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi there,<br><br>I don't work too much with vectors, but my personal experience with them has been fairly slow, perhaps due to the topology. If you have access to the raw point cloud, you could try importing the ground and surface points as separate rasters using r.in.xyz and then use r.mapcalc to get the height by subtracting the ground from the surface raster. Or do you definitely need vector points as an output?<br>
<br>Best,<br>Daniel<br clear="all">
<p style="margin-top:0px;margin-bottom:0px;margin-left:0px;margin-right:0px;text-indent:0px"><span style="font-size:13px;font-family:arial,sans-serif"></span></p><p>--<br></p><p>B.Sc. Daniel Lee<br>
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Zusätzliche Unterstützung erhält ISIS von dem Entrepreneurship Cluster Mittelhessen, der Universität Marburg, dem Laboratory for Climatology and Remote Sensing und dem GIS-Lab Marburg.</p><p></p><br>
<br><br><div class="gmail_quote">Am 29. März 2012 22:59 schrieb Daniel Victoria <span dir="ltr"><<a href="mailto:daniel.victoria@gmail.com" target="_blank">daniel.victoria@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi all,<br>
<br>
I'm trying to calculate the height from the ground of several lidar<br>
points (15million) in order to get the number of points that occur at<br>
different height levels. I read some older posts about using r.in.xyz<br>
(or r.in.lidar in grass 7) but I could not understand how to count the<br>
number or points that have height from 0 to 5 m above the ground, for<br>
instance. So, I'm trying to do the following.<br>
<br>
1) import points using v.in.lidar (Grass 7 ubuntu linux)<br>
2) create a column in the database for the ground height and one for elevation<br>
3) populate height column from ground raster (generate in another<br>
process) using v.what.rast<br>
4) calculate elevation as zcoord - ground for each point (v.db.update)<br>
<br>
As you might imagine, this takes a long time. Just to import a 400Mb<br>
lidar file takes around 50min.<br>
Is there any easier way that I'm not envisioning?<br>
<br>
I'm running Grass 7 with liblas on a Ubuntu Virtual Machine and sqlite backend.<br>
<br>
Thanks<br>
Daniel<br>
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