Update _slice_collection to use toBands and select

[boothmanrylan]

Avoids the expensive call to toList unless the ImageCollection contains more than 5000 images and we are slicing past the 5000th image.

Fixes https://github.com/google/Xee/issues/88 where xee wasn't recognizing new bands added to existing images or renamed bands.

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[alxmrs]

Thanks for the explanation! That makes sense to me. I see how this works around the limits rather than the specifics.

On Sat, Nov 4, 2023 at 3:31 AM Rylan Boothman @.***> wrote:

@.**** commented on this pull request.

In xee/ext.py https://github.com/google/Xee/pull/91#discussion_r1381954762:

@@ -679,31 +679,19 @@ def _slice_collection(self, image_slice: slice) -> ee.Image:

Get the right range of Images in the collection, either a single image or

a range of images...

start, stop, stride = image_slice.indices(self.shape[0])

• If the input images have IDs, just slice them. Otherwise, we need to do

• an expensive toList() operation.

• if self.store.image_ids:
• imgs = self.store.image_ids[start:stop:stride]
• selectors = list(range(start, stop, stride))
• col = self.store.image_collection.select(self.variable_name)
• if self.shape[0] <= 5000: # 5000 == max bands in an Image
• col_as_image = col.toBands()
• return col_as_image.select(selectors)
• elif stop < 5000: # 5000 == max bands in an Image

I don't think so. Even if the start/stride arguments would make the final image have fewer than 5000 bands, I'm avoiding toList by converting to a multiband image before slicing so I need to grab the first "stop" bands and toBands will fail if it would return an image with more than 5000 bands.

— Reply to this email directly, view it on GitHub https://github.com/google/Xee/pull/91#discussion_r1381954762, or unsubscribe https://github.com/notifications/unsubscribe-auth/AARXAB77ASVIM3FZUJRBHQLYCUL6BAVCNFSM6AAAAAA627ORW6VHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHMYTOMJTGEYTMNRZGY . You are receiving this because you commented.Message ID: @.***>

[boothmanrylan]

Discussion with Noel Gorelick on Earth Engine Developer forums about a more efficient way to slice an image collection: https://groups.google.com/g/google-earth-engine-developers/c/fSAo9Jn615U

The recommendation was to get a list of system:index, slice that list, then filter the image collection for the remaining system:index

[alxmrs]

What is the difference between a system:id and a system:index? We do something similar to the suggestion with ids.

I have a hunch that the recommended approach won’t work for all cases, and thus we need a toList() or toBand() alternative implementation.

On Tue, Nov 7, 2023 at 2:00 AM Rylan Boothman @.***> wrote:

Discussion with Noel Gorelick on Earth Engine Developer forums about a more efficient way to slice an image collection: https://groups.google.com/g/google-earth-engine-developers/c/fSAo9Jn615U

The recommendation was to get a list of system:index, slice that list, then filter the image collection for the remaining system:index

— Reply to this email directly, view it on GitHub https://github.com/google/Xee/pull/91#issuecomment-1795029027, or unsubscribe https://github.com/notifications/unsubscribe-auth/AARXAB5N2KOGKFYXGGEUG5TYDD3R7AVCNFSM6AAAAAA627ORW6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTOOJVGAZDSMBSG4 . You are receiving this because you commented.Message ID: @.***>

[boothmanrylan]

We likely need someone more familiar with earth engine's internals than I am to confirm this, but I believe the main differences between system:id and system:index are:

• system:id is a unique identifier of an object from one of the collections in earth engine's data catalogue while system:index is a unique identifier of an object within the specific context of one collection. This means you can use the system:id to load an image from the data catalogue, but you cannot use the system:index to do this because the system:index is specific to one collection that could be user created.
• system:id behaves like a regular property (i.e. it can be modified and it isn't guaranteed to exist) while system:index behaves differently (it is automatically created if you create a collection of constant images and it cannot be modified by mapping over a collection)

I think the issue with how system:id was originally being used comes from here:

 col = ee.ImageCollection(imgs)

Because this reloads the raw images from the data catalogue and therefore throws out any modifications that a user made to the collection beforehand.

I'm not sure that its possible to have an image collection without the images all having a unique system:index, but I will add the alternative methods back in as a fail safe because I'm not 100% certain of that.

Relevant gis stackexchange answer: https://gis.stackexchange.com/a/390307 Earth engine script where I was messing around with system:id and system:index: https://code.earthengine.google.com/8eb85fdb77aeb1adca98fe5eaa36246c

[naschmitz]

@boothmanrylan Could you sync and resolve the conflicts? Then, I can approve and run the integration tests against your PR.

[boothmanrylan]

@naschmitz I resolved the conflicts.

The tests are passing for me locally, but failing here on the "Authenticate to Google Cloud" step which I'm not sure how to resolve. If there is something I need to change to get that to work please let me know.