[Qgis-user] Select heights from a raster layer

[Neumann, Andreas]

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 
>> 
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