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I need to georeference historical aerial images (from 1976). There is no metadata, e.g. reference system, available. I thought I could use Google satellite to set ground control points for georeferencing.

However, I am not sure if this is precise enough. Has anyone experience on the quality of georeferenced images via Google?

  • You can compare Google imagery with geodata from the official survey authority to see how good it is. – AndreJ Dec 17 '18 at 13:30
  • Precise enough for what? – Dan C Dec 17 '18 at 14:56
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I good source that I can point to for you to reference would be Google Earth For Satellite Image Geo-referencing

Abstract
Google earth is widely used, when working with geo spatial data for extracting point data and geo-referencing low resolution image . However, the accuracy of Google Earth is not defined. Our project carried out around AIT was to simply find the accuracy of, point coordinates extracted for Google Earth with DGPS coordinates. GPS observations were carried at GIC building, AIT Pool, road junctions, and basketball court as shown below. Coordinates for the Google Earth x,y columns in the following tables has be picked keeping "Eye alt ≈300m" to avoid errors in pin-pointing position on Google Earth. GPS observations has been corrected using DGPS techniques. Error in picking actual point in Google Earth has been neglected.

Conclusion
This shows that Google Earth is more than enough for geo-referencing low-resolution image that has 25m-30m resolution.

The accuracy of the point can be brought down to approximately 0.5m in X direction by adding -4.27m and approximately to 0.8m by adding -2.4m in y direction.

Application of this error in other areas can change due to the projection errors in Google earth.

To get a real idea of the accuracy the point extraction should be carried out covering a wide area.

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At least when using QGIS I have noticed that, depending on where the area of interest is, Google Maps tends to be offset to varying degrees. It depends on the level of precision you need also, if it's not very important than you might get away with it but if you need a high degree of accuracy then no they do not project accurately enough.

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Google imagery offers some degree of confidence - X and Y accuracy. You can use it depending on what you want to extract from your aerial images. If you need quantitative measurements such as an area with a high degree of accuracy then no. Otherwise, if you just want to use it as a reference for displaying purposes then go ahead.

You could ask google about the method they use and if they have guidelines for imagery assessment and scale precision. I do believe it will vary according to the geographic region though.

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