On Sat, May 21, 2011 at 8:22 PM, Michael Kimmerly <[email protected]>wrote:
> The gdal_warp -clipper plugin in Qgis appears to be a real life-saver for > me > in my use of Qgis in doing NDVI analysis in agriculture where I need to > clip > my data to a particular farm or field that may be quite irregular in shape. > However, I am having difficulties getting the plugin to properly trim to > the > extent that I want to end up with. > > My process is: > > 1. I am loading a landsat scene for my data. > 2. Creating a shapefile layer and digitizing a polygon of the area that I > want to analyze. > 3. Select the polygon and save as a separate shapefile. > 4. Perform the clipper function on the landsat raster using the saved > polygon shapefile as my mask. > > Not sure if step 3 is necessary but want to make sure the mask is limited > to > only the polygon that I digitized. Also the mask polygon may come from an > already existing shapefile that may have been gps'd or previously digitized > from some other source. > > The resulting raster is clipped to the polygon but the extent is still the > original landsat. From gdal documentation appears that the -crop_to_cutline > needs to be included in the plugin. Am I correct in this or am I missing > some step? > > Thanks for any help. > This is how I have achieved what you are seeking in my past experience; 1. Load image 2. Load vector mask for clipping of image 3. Find extent of clipping vector mask, and perform a rectangular clip of the image 4. Perform the vector mask clip I suppose you could always to the rectangular clip after the vector mask clip also. There should be a way to automate this task, retrieve extent of vector mask and automate rectangular clip either before or after the vector mask clip. Mars
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