3rd order image calibration

[ErichZimmer]

Is your feature request related to a problem? Please describe.
During some experiments, lense distortion or not being perpendicular to the laser sheet makes measurements inaccurate.

Describe the solution you'd like
Use the instructions based off of the article Distortion correction of two-component - two-dimensional PIV using a large imaging sensor with application to measurements of a turbulent boundary layer flow at Re = 2386. The calibration script should be placed in its own file or in OpenPIV.tools.

[alexlib]

@ErichZimmer - please add here a link to the repo with your tests or the algorithm. Thanks

[TKaeufer]

Hey Erich,

I already implemented some kind of mapping based on polynoms. I add you to the repo.

[ErichZimmer]

I have access to Alex's fork, and I like your script. It is sort of similar to the aformentioned article and a lot faster than my implementation which uses lots of for-loops.

[ErichZimmer]

I used your script on an experiment, and it worked pretty well on deforming non-optimal calibration images. Worked on skewed images too. The interface (v2 file) was easy for me to use and I think it's simple enough to include it in OpenPIV as a pre/post processing method.

[ErichZimmer]

I wasn't able to make a "nicer" version of the script without sacrificing speed or accuracy. I think it is good as is. What do you think, @alexlib ?

[ErichZimmer]

Is there a reason why the output dewarp image appears to be inverted in the y axis? With the image coordinate system (e.g. origin top left), the image has to be inverted along the y axis for some reason. Could be user error, but I'll see in a few days.

[alexlib]

I didn't notice it. But, you know the best is to show this in an example - and we'll try to take a look.

[ErichZimmer]

It was user error, nothing wrong so far...

[ErichZimmer]

Is there anyway to simplify the code for _calculate_scale by using the aformentioned article?

[ErichZimmer]

Additionally, we should add a plot like the following so a user can observe the deformation pattern.
Note, the plot is centralized, not normalized.

[alexlib]

_calculate_scale

what do you mean by simplify? https://github.com/TKaeufer/Open_PIV_mapping/blob/7fd62ed05e35030d3e98ce1b64cfa55d4357c435/calibration_functions_cleaned_v2.py#L152