How do I apply a fitgeotrans output or similar to points NOT an image?

Question

Right Grievous 2016-6-18

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https://ww2.mathworks.cn/matlabcentral/answers/290703-how-do-i-apply-a-fitgeotrans-output-or-similar-to-points-not-an-image

编辑： kuroshiba 2022-12-2

Hi everybody,

I have been using the fitgeotrans function to find the best linear weighted mean transformation between two sets of points.

This works really well when I use the imwarp function to warp an image, however, I also need to perform the same transformation on x,y points - this is proving difficult.

The tform output of fitgeotrans does not seem to have any transformPointsForward method, all it has is a transformPointsInverse method, which is not useful for me.

I think I must be missing something, the fitgeotrans function is using point coordinates to calculate the transformation, so surely it should be as easy to apply this to coordinates as well as images, if not easier?

Thanks for any help,

Rod.

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Answer 1

Catalina Vajiac 2016-6-24

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https://ww2.mathworks.cn/matlabcentral/answers/290703-how-do-i-apply-a-fitgeotrans-output-or-similar-to-points-not-an-image#answer_226627

There is a transformPointsForward function that you can use on your data points. The issue is that they are then defined in world coordinates, not intrinsic coordinates, so you must also use the worldToIntrinsic function, like this:

[B,RB]=imwarp(A,tform);

[xdataT,ydataT]=transformPointsForward(tform,xdata,ydata);

[xdataI,ydataI]=worldToIntrinsic(RB,xdataT,ydataT);

where tform is the output from fitgeotrans and RB is a spacial referencing object.

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Sudip Paudel 2020-5-27

编辑：Sudip Paudel 2020-5-27

I ran into the same issue and tried this method. However, it did not work for me because I am using transformation type 'lwm'. Is there another approach to solve this issue?

kuroshiba 2022-12-2