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How can I extract values from a raster by points. I prefer not in Arcgis. I prefer in Qgis or Mapwindow or other open source gis.

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1  
So you have points and you need to extract the values from the raster under those points, or do you need to convert the raster cells into points. Just checking before I try and work out the answer. –  Nathan W Nov 16 '10 at 11:07
    
The first, i have the points and i need to extract thevalues from the raster, under those points. THNX!! –  Vassilis Nov 16 '10 at 12:50

7 Answers 7

up vote 14 down vote accepted

QGIS "Point Sampling Tool" should be the plugin you're looking for.

Here's a detailed description of how to use it: http://pvanb.wordpress.com/2010/02/15/sampling-raster-values-at-point-locations-in-qgis/

Update based on Paolo's comment:

the plugin is not the only solution, and not always the easiest solution anymore. An alternative solution is the Saga function ‘Add grid values to point’ in the processing toolbox. See for details http://pvanb.wordpress.com/2014/07/01/sampling-raster-values-at-point-locations-in-qgis-an-update/

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yes easier this way with the plugin –  Mapperz Nov 16 '10 at 14:56
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People are still finding the above-mentioned post through this Q&A. However, the plugin is not the only solution, and not always the easiest solution anymore. An alternative solution is the Saga function ‘Add grid values to point’ in the processing toolbox. See for details this post. –  Paulo Jul 4 at 10:17

Hawthorne Beyer's GME tools do this nicely via command line, and allow easy batching with 'for' loops.

isectpntrst(in="path/to/shapefile", raster="path/to/raster", field="fieldname")

GME isectpntrst command reference

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In PostGIS 2.0 you can do:

SELECT ST_Value(rast, geom) val
FROM yourrastertabe, yourpointtable
WHERE ST_Intersects(rast, geom)

Make sure your raster is tiled very small when you load it (-t 10x10 with the loader).

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MAKE SURE THE RASTER FILE IS TILED VERY SMALL (-t 10x10) –  nickves Jan 23 '13 at 12:10

In GRASS GIS, you can either query the map in the GUI or use http://grass.osgeo.org/gdp/html_grass64/r.what.html

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For Grass I found this:pvanb.wordpress.com/2010/05/05/… –  Vassilis Nov 19 '10 at 8:58

A quick thought, http://gis-techniques.blogspot.com/2012/10/extract-raster-values-from-points.html has step by step guide to use R Raster package extract raster values from points. Now days R raster package is popular for raster handling in terms of resource, easiness and quick and dirty job done.

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If you have access to FME then you can use one of two transformers in FME Workbench.

The RasterCellCoercer ("Decomposes all input numeric raster features into individual points or polygons. One vector feature is output for each cell in the raster.")

The PointOnRasterValueExtractor ("Takes in point features and a single reference raster. The output consists of the band and palette value(s) at the location of each point.")

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No I don't have or use FME, is a standalone application or a plugin? –  Vassilis Nov 26 '10 at 9:14

Quick thought:

  1. gdal_polygonize.py - polygonize your raster feature
  2. Insert your point features and polygons into PostGIS database
  3. Use st_intersects function to pull all elevation values where features intersect
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interesting approach, because yesterday start studing how to use Postgis. –  Vassilis Mar 12 '12 at 20:35
    
Thanks, it's fairly simplistic but it works. Here is what I was able to produce with this approach: i.imgur.com/h8CGJ.png –  user5584 Mar 14 '12 at 13:58

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