Constraining solution space of estimateGe​ometricTra​nsform()

The last time I used estimateGeometricTransform() I had to manually deal with solutions that were of no interest. E.g. I wouldn't want to consider scaling, or I would like to consider scale factor in a certain range e.g. 2% of the original (meaning I'm confident the image is essentially rotation and translation), how would I make estimateGeometricTransform constrain its optimisation.

Thanks.