[Qgis-user] aligning ortophoto with google maps and google earth

[Greg Troxel]

Nigel Berjak - General via QGIS-User <qgis-user at lists.osgeo.org> writes:

> Please be careful to think that Google Earth is more accurate than
> your drone aerial imagery. Google Earth imagery suppliers may not have
> a DEM that is accurate, often for places/locations that are not
> considered high-value e.g. places likely to be visited by people on
> Google Earth, those that have not been commissioned at a high level
> for spatial accuracy etc. You would need to determine from the imagery
> source of the Google supplied imagery, what that scene is produced
> at. If you have a national spatial body for your country, it is likely
> their DEM will be more accurate.

Also, please read the google terms carefully, and see if what you are
trying to do is permitted, or if you have agreed not to do it.

In general, for aligning a raster image (that is more or less
orthorectified), see the Georeferencer.  You'll need Ground Control
Points.  Two normal approaches:

  Find some places in the imagery that are clear in the imagery, and use
  RTK to measure ground coordinates.  Be careful about datum.

  Find some places in imagery that are clear, as above, and instead find
  corresponding points in some imagery that you believe to be aligned,
  whose terms permit you to use it.   Or, use a vector road dataset,
  again with confidence in the data and licensing permission.