I'm georeferencing old arial photos with a commercial GIS. The software offers me 'Affine', 'Bilinear' and 'Helmert transformation' as transformation options. Unfortunately, the support of the GIS can't really tell me what the differences are and which option to choose in what situation.

All three give me slightly different results. Perhabs someone with knowledge in Transformation can explain me that option X is good in heterogeneous surfaces while Y is good for a cetain typ of arial photos or something like that?

When to choose which option?

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    I'm not an expert, but in think this tools are not the best (affine: translation and scaling; helmert tranlation, scale and rotation). With old aerials photos you need to correct the perspective and lens effect. In the past, i have made a orthophotographie with the free "Hugin", and than it was easier to georefence in qgis Nov 23 '20 at 8:41

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