How to Digitize Free Satellite Imagery in QGIS?

Question

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?

Answer 1

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.

Answer 2

• Some providers of imagery say you should not;

http://www.google.com/permissions/geoguidelines.html

• When the plugin is opened, it automatically sets the CRS to 900913 or 3785. That is good, don't change it.

Once the CRS is set, if you zoom in too much (say 2500 depending on where in the world you are) positional accuracy is broken.

Answer 3

There is a bug in the Openlayers plugin that affects only Google imagery in higher zoom levels. When reaching the highest zoom level available, the tiles are not enlarged or removed when zooming in further, but misaligned.

There is already a ticket for that: http://hub.qgis.org/issues/6822

I did not exerience that behaviour when using bing imagery or OSM tiles. So you may take those as reference or alternative.

Answer 4

Make sure the data you're creating matches the projection from OpenLayers (I think it is EPSG:3857). Once you finish digitizing you can reproject the data to the projection you use in your day to day work.