8000 Add "imshow" as an option for autoalign plotting of maps · Issue #6812 · sunpy/sunpy · GitHub
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Add "imshow" as an option for autoalign plotting of maps #6812

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ayshih opened this issue Mar 1, 2023 · 11 comments · Fixed by #8036
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Add "imshow" as an option for autoalign plotting of maps #6812

ayshih opened this issue Mar 1, 2023 · 11 comments · Fixed by #8036
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Effort Medium Requires a moderate time investment. Feature Request New feature wanted. map Affects the map submodule Package Intermediate Requires good technical knowledge of the package. Priority Low Rapid action not required.

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@ayshih
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ayshih commented Mar 1, 2023 •
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For autoalign plotting of maps, our current implementation uses pcolormesh(). However, if the pixel-to-pixel transformation between the map's WCS and the axes's WCS is affine (i.e., just scaling and rotation), using imshow(transform=...) would have much better performance than pcolormesh(). The trick is that we'd have to add a clip path to the image produced by imshow() because it can unnecessarily extrapolate data.

We should add imshow() as an option for autoalign plotting.
@nabobalis nabobalis added Feature Request New feature wanted. map Affects the map submodule Priority Low Rapid action not required. Effort Medium Requires a moderate time investment. Package Intermediate Requires good technical knowledge of the package. labels Mar 1, 2023
@ayshih ayshih mentioned this issue Mar 1, 2023
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@Mihan786Chistie
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For autoalign plotting of maps, our current implementation uses pcolormesh(). However, if the pixel-to-pixel transformation between the map's WCS and the axes's WCS is affine (i.e., just scaling and rotation), using imshow(transform=...) would have much better performance than pcolormesh(). The trick is that we'd have to add a clip path to the image produced by imshow() because it can unnecessarily extrapolate data.

We should add imshow() as an option for autoalign plotting.

Hey @ayshih, can you explain "The trick is that we'd have to add a clip path to the image produced by imshow() because it can unnecessarily extrapolate data."

@ayshih
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ayshih commented Apr 4, 2023

Look at the middle panel of the figure in this comment, and then the addition of a clip path in this later comment.

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@Mihan786Chistie Mihan786Chistie mentioned this issue Apr 4, 2023
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@Prtm2110
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Hello, what will be the clip path for a map object? Any resources on this will be helpful.

w = data.shape[1]
h = data.shape[0]
path = mp.path.Path([[-0.5,-0.5], [w-0.5,-0.5], [w-0.5,h-0.5], [-0.5,h-0.5], [-0.5,-0.5]])

This clip path from astropy/astropy#14420 (comment) don't seem to be general for all?

@ayshih
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ayshih commented Jan 24, 2025

Those are correctly the pixel coordinates for the four corners of any map. However, the approach of imshow() plus such a clip path works fully only when the pixel-to-pixel transformation between the map's WCS and the axes's WCS is affine (i.e., just scaling and rotation). This stringent requirement means that we'd want to detect when the imshow() approach may be providing a flawed image and emit a warning.

@Prtm2110 Prtm2110 mentioned this issue Jan 24, 2025
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Prtm2110 commented Jan 24, 2025 •
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Thank you for the response! "pixel-to-pixel transformation between the map's WCS and the axes's WCS is affine" how do I exactly go on do this, my rough guess is to check if wcs.cdelt and wcs.pc exits or this is not the right direction I am heading in? Additionally could you please review #7772 if the work done there is correct or any requires changes.

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Effort Medium Requires a moderate time investment. Feature Request New feature wanted. map Affects the map submodule Package Intermediate Requires good technical knowledge of the package. Priority Low Rapid action not required.
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Adds an imshow-based option for autoalign plotting of maps Prtm2110/sunpy
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@ayshih @nabobalis @Mihan786Chistie @aritrasinha108 @Prtm2110
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