digitizingqgisqgis-openlayers-plugin
I am trying to digitize OpenLayers data (such as Google satellite imagery) with no success. Whenever I try to move or zoom the canvas the vector layer I digitized loses the position relative to the imagery.
I have read about this problem elsewhere but was not able to find a solution.
Does anyone have a solution as to how I can digitize satellite imagery for free in QGIS?
In QGIS, use the Clipper raster tool, under the Raster-> Extraction menu. See: Clipping raster with vector boundaries using QGIS?
You may have issues trying to clip data in a plugin layer (e.g. Openlayers) because the Clipper function requires a input graphic file (raster) from disk. Your best bet is to get the satellite imagery directly from the source and load that into QGIS.
Check here for most from Landsat missions:
USGS Global Visualization Viewer
Once you get it working in QGIS, delve into the gdalwarp utility (see code generated at bottom of Clipper dialog) to see about scripting your clippings (via bash or Python).
If you have installed QGIS using the KyngChaos.com frameworks, then gdal and its utility programs are located in:
/Library/Frameworks/GDAL.framework/Versions/1.9/Programs
Read the README included with the KyngChaos.com installers to see about updating your bash (Terminal) PATH environment variable.
EDIT: In your scripting you will need to loop through the features of your shapefile (used here as a cutline) and spatially match it up to the appropriate imagery. Alternatively, if it is a one-off project, you can export features to separate shapefiles using the Split vector layer tool, located under the Vector-> Data Management Tools menu. It may make your life easier when learning to make your first batch scripts.
Use the QuickMap Services plugin instead. It works well and doesn't have the issues that were reported in Print Composer. See this post
Best Answer
For he time being at least you might be better off digitizing your shapes directly in Google Earth and saving them as KML (not KMZ) ready for importing to QGIS, where they can be reprojected to your required CRS.
N.