Calculate accuracy of georeferencing

Question

I'm working on georeferencing old maps for archaeological purpose. Of course, colonial maps all do have some degree of transformation needed. But sometimes a specific region is well mapped while the neighbouring one is not. So I wonder if there is a way to calculate the amount of (in)accuracy, or the level to which the original image has been transformed in order to fit the actual landscape? Could a new raster be generated with these values? I'm using QGIS and TPS for georeferencing, but it can be on any platform.

Swarley · Answer

Load the maps shapefile from a trusted source and compare them. If there is some error it can be further improved by taking more control points, changing transformation parameters and trying a different datum.

Answered by Swarley on August 16, 2021

John Thorn · Answer

I'm not sure if this is what you want but when you load a map with 4 or more calibration points in MAPC2MAPC, it calculates a best-fit affine transformation between coordinates and pixels - and then reports on how good the fit is.

If you have an image and a suitable calibration file it will only take seconds.

But what to do if the calibration is 'off' is another matter!

http://www.the-thorns.org.uk/mapping/help/errors.html

Calculate accuracy of georeferencing

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