Hi Andreas (and others who have answered our questions), “Zonal Statistics” do not exactly do the job, it also do the next step in our task!
In fact our intentions was to select the surface heights (measured from a flight with laser in a 1,6mx1,6m grid) only inside the buildings polygons and then export the roof heights (still in a 1,6mx1,6m grid ) to a another program. In this program the mean heights of all buildings should be calculated and attached to the buildings. Now we can use “Zonal Statistics” (and only select the mean-calculation) and then we have the mean height as a new feature value for each building. Perfect! We did tried the “Zonal Statistics” earlier but couldn’t comprehend were the calculated values ends (there was a cryptic “Band”-drop down in “Zonal Statistics” form). I still don’t understand the “Band”-drop down, but so what, it works. Thank you very much. Venlig hilsen / Best regards Claus Backalarz Senior specialist DELTA Acoustics ________________________________ DELTA| Venlighedsvej 4 | 2970 Hørsholm | Denmark | madebydelta.com<http://madebydelta.com> [email protected]<mailto:[email protected]> | tel: +45 72 19 40 00 | direct: +45 72 19 46 00 | mobile: +45 24 44 08 78 [cid:[email protected]] We help ideas meet the real world ________________________________ From: Qgis-user [mailto:[email protected]] On Behalf Of Neumann, Andreas Sent: 10. marts 2016 17:46 To: Richard McDonnell Cc: [email protected] Subject: Re: [Qgis-user] Select heights from a raster layer Hi, Have you tried the "Zonal Statistics plugin"? After enabling this plugin, you can find it in the raster menu - or maybe it is already there by default. It calculates count, sum, min, max, mean at the intersection of a polygon layer (e.g. your polygon layer with building footprints) and a given raster layer (your grid based terrain model). I think it does what you want. Hope this helps, Andreas On 2016-03-10 17:37, Richard McDonnell wrote: Claus, It may not be exactly what you want, but one suggestion would be to derive the centroids from the building polygons (making sure there within the polygon) and then use the point sampling tool to pull the elevations from your DSM. of course that will not guarantee that you get the max height If you can, it may be best to go back to the DSM source, the raw data used to derive the DSM. If it is, for instance a point cloud dataset, like that from Lidar, you could select all points within your polygons, then extract only the points at the apex (first returns), just a thought. Regards, Richard On 10/03/2016 11:52, Claus Backalarz wrote: Hi, we are novices in the QIS-world so bear with misunderstandings and misconceptions. We have a raster layer with surface heights called DSM_611_86. Originally it is was a plain text file with a header describing number of rows and columns, geographically lower left corner etc. Data was the surface heights in 6250 rows and 6250 columns. The file was imported without problems with "Add raster layer" in QGIS. It is beautiful showed in QGIS2.14 Essen on Windows 7. So far no problem. But we want with (a lot) of polygons representing buildings to select all surface heights inside this polygons. The selected heights should afterward be saved as a reduced raster layer or, even better, as a shape file of points with an attribute for the heights. In other words as a layer of points with one and only one attribute, the surface height. We have tried the plug-in "Point Sampling Tools" and some other hints from QGIS home pages, but I seems that select and save heights in the described way is "out of scope". Do anybody have a useful way out of this problem ? Best regards Claus B The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer. _______________________________________________ Qgis-user mailing list [email protected]<mailto:[email protected]> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user -- Richard McDonnell GIS Specialist PgD GIS AssocSCSI OPW FRM Data Management 52 Stephens Green, Dublin 2. 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