[GIS] Why does Clip function (maintain clipping extent) not clip according to polygon feature

arcgis-desktopclipraster

In arcGIS 10, I have several raster maps, that I would like to clip according to a polygon feature (top map). I have tried the Clip function under Raster Processing<-Raster<-Data Management Tools, and ticked off the Maintain Clipping Extent box. I am not allowed to tick off the Use Input Features for Clipping Geometry box.
But I end up with a map of the same extent but different shape than my polygon (bottom map). I really need the map to have the same extent and size of the polygon. I have tried un-ticking the Maintain clipping Extent box, but it makes no difference with regards to the result.
I have added a picture of what I entered in the Clip box, and what the process looked like after the maps.

Best Answer

Try to dissolve the polygons and create only one polygon and use that as a clip polygon. But make sure the projection for both the raster and polygon shapefile is same. Different projections will not give you the desired result. Because if the projections of input polygon and raster are different, the clip based on feature extent will not be activated.

If dissolve didn't solve the problem to get one polygon (the outline polygon), try to make a copy of the input polygon shapefile, then click on start editing of the new copied shapefile and select all polygons then merge them all to get only one polygon (the outline polygon). Then follow the above process.

Related Solutions

[GIS] Why does clipping a raster alters cell size

I have used the GDAL tools to rasterize a vector and providing the extension of my desired raster worked but if the data was very specific(i.e. lots of decimal points) I still didn't obtain the extension I needed. So I tried different things that worked in different ways:

a) I modified my rasters to the desired pixel size. If I created a raster from vector I followed this tutorial: http://www.mikemeredith.net/blog/1212_GIS_layer_for_Distance_from_in_QGIS.htm This indicates in the editable box where to provide the pixel size. It also indicates how to provide extension but because my extension was very "long" that didn't work for extension only for pixel size.

b) If you are using QGIS and are preparing your environmental layers for Maxent I suggest using the QSDM plugin and unify all your layers. All layers need to be in the same format (.tiff),same CRS and it helps if they have the same resolution. They will be given an equal extension as new layers that have been "unified". Even if they don't seem like they are the same, checking the metadata will confirm that they have been modified to have the same extension and resolution. Ready to be used in Maxent.

c) Additionally there is a nice tutorial here for Maxent AND QGIS, check out the: "Creating new rasters with GDAL tools" section. Where they cover re-sampling and this is great if you want to change pixel size for your environmental layers. http://clp-foss4g-workshop.readthedocs.org/en/latest/qgis_raster_resample.html

Hope it works and if there are other ways that worked for you I would be happy to know as sometimes for us beginners it is a lot of trial and error.

GDAL – How to Clip Polygon Precisely to Raster Extent Using GDAL

You can use GDAL's ogr2ogr utility (http://www.gdal.org/ogr2ogr.html) to clip a polygon by an extent. If you have GDAL for Python you can use something similar to this script to perform the task:

from osgeo import gdal
import subprocess

# define file paths
inRasterPath = 'C:/path/to/file.tif'
inVectorPath = 'C:/path/to/file.shp'
outVectorPath = 'C:/path/to/file.shp' 

# get the extent of the raster
src = gdal.Open(inRasterPath)
ulx, xres, xskew, uly, yskew, yres  = src.GetGeoTransform()
sizeX = src.RasterXSize * xres
sizeY = src.RasterYSize * yres
lrx = ulx + sizeX
lry = uly + sizeY
src = None

# format the extent coords
extent = '{0} {1} {2} {3}'.format(ulx, lry, lrx, uly);

# make clip command with ogr2ogr - default to shapefile format
cmd = 'ogr2ogr ' + outVectorPath + ' ' + inVectorPath + ' -clipsrc ' + extent

# call the command
subprocess.call(cmd, shell=True)

If you don't have GDAL for Python, you can use the OSGeo4W shell that comes with QGIS and run the gdalinfo command on your raster to get the extent and then the ogr2ogr command to clip the vector to the extent noted from the gdalinfo result with the -clipsrc flag.

Make sure your polygon and raster file are in the same projection.

Best Answer

Related Solutions

[GIS] Why does clipping a raster alters cell size

GDAL – How to Clip Polygon Precisely to Raster Extent Using GDAL

Related Question