STAC support (a STAC layer group) #14927

m-mohr · 2023-07-20T20:27:09Z

This PR proposes to add STAC capabilities to OpenLayers. It adds a STAC LayerGroup.

The layer group creates various layers depending on the given options and what the STAC entity offers, e.g. footprints, COGs and thumbnails. What usually is the source is the stac-js library here.

Examples: https://deploy-preview-14927--ol-site.netlify.app/en/latest/examples/?q=stac

The work is based on PR #14101 from @tschaub (he's aware of this work).
The interface is mostly aligned with the stac-layer library for Leaflet (https://github.com/stac-utils/stac-layer), which is also based on stac-js and offers pretty much the same functionality.

An important question is whether this is something for OL core or whether I should publish this as an extension.

The functionality implemented here includes:

Todos:

Projection handling for GeoJSON (see STAC support (a STAC layer group) #14927 (comment) )
Support passing HTTP headers with the requests (via the GeoTiffSourceOptions)
(Basic) support for STAC web-map-links extension
Easy retrieval of STAC entities for events (see STAC support (a STAC layer group) #14927 (comment))
Tests (I'll start this once I know whether this will live in the OL repo or not)

Curious to get thoughts from others and maybe point me to things that can be improved.

PS: The work on this was funded by Planet and EOX.

github-actions · 2023-07-20T20:36:29Z

📦 Preview the website for this branch here: https://deploy-preview-14927--ol-site.netlify.app/.

jahow · 2023-07-21T08:57:12Z

Impressive work @m-mohr, thanks!! since you're asking for feedback here are a few things that came to my mind when reading your PR. Note that some aspects of the PR may have already been discussed and agreed on so this is just my opinion!

The fact that the STAC layer can create other layers (e.g. in case of a collection of items) is uncommon for layers in the library; this might make things awkward for users e.g. for specifying layer options (should layer options be applied to all created layer?) or getting back these layers without searching through the layer tree
More generally, it feels like the STAC layer is doing too much magic: using a XYZ or Geotiff source depending of where tiles are computed, using a vector source for the footprint and a static source for the preview... I think the API would be more explicit and straightforward with utilities like readStacItem and readStacCollection (naming probably dumb) that would then allow the user to explicitly create the type of layer and source they want according to the assets found; it might be significantly more verbose though
I would externalize STAC-related utilities to make the STAC layer file lighter (see for example https://github.com/openlayers/openlayers/blob/main/src/ol/source/ogcTileUtil.js)
Some examples have logic for reading layer titles as well, but this doesn't show up visually (it looks like it's expecting a layer tree ?)

Again, this is just my opinion and not a definitive review. And it's great to see first-class STAC support coming in OpenLayers!

m-mohr · 2023-07-21T09:25:07Z

Thank you for your feedback @jahow, I appeciate it!

The fact that the STAC layer can create other layers (e.g. in case of a collection of items) is uncommon for layers in the library; this might make things awkward for users e.g. for specifying layer options (should layer options be applied to all created layer?) or getting back these layers without searching through the layer tree

This is something we could improve, of course, e.g. by having options like geotiffOptions, xyzOptions that are passed through. We could also specify a property for each layer for identification purposes.

More generally, it feels like the STAC layer is doing too much magic: using a XYZ or Geotiff source depending of where tiles are computed, using a vector source for the footprint and a static source for the preview... I think the API would be more explicit and straightforward with utilities like readStacItem and readStacCollection (naming probably dumb) that would then allow the user to explicitly create the type of layer and source they want according to the assets found; it might be significantly more verbose though

That's why it is a LayerGroup, of course. If you just want XYZ or GeoTiff or VectorLayer, stac-js makes it very simple to just use those separately, but then you don't need any STAC integration at all in OL, I think. The LayerGroup is meant to make life very easy and give a consistent rendering behavior for STAC. But I can understand that this might be too much magic for the core OL library. In that case an option could also be to just include the change to the GeoTiff in this PR, and then keep the magic/LayerGroup as extension outside of this repo. Also fine with me. Just let me know what the maintainers think about it.

I would externalize STAC-related utilities to make the STAC layer file lighter (see for example https://github.com/openlayers/openlayers/blob/main/src/ol/source/ogcTileUtil.js)

Sure, I've created a stacUtil.js to externalize some of the code. Other than that, I'd need to dig a bit deeper to see what makes sense. If you have something obvious in mind, please let me know.

Some examples have logic for reading layer titles as well, but this doesn't show up visually (it looks like it's expecting a layer tree ?)

Yeah, I think it was for debugging purposes at some point. I could add a layer switcher there, which could help visualize the layer tree structure. Not sure whether that's something you would want in an example though?

src/ol/layer/STAC.js

src/ol/layer/stacUtil.js

ahocevar · 2023-08-02T16:56:55Z

src/ol/layer/STAC.js

+      const features = new GeoJSON().readFeatures(geojson, {
+        featureProjection: 'EPSG:3857', // TODO: revisit this
+      });
+      const source = new VectorSource({features});
+      const vectorLayer = new VectorLayer({
+        source,
+        style: getBoundsStyle(this.boundsStyle_, this),
+      });
+      vectorLayer.set('bounds', true);
+      features.forEach((feature) => feature.set('stac', data));


A few thoughts here:

If you configure the source with a loader instead of features, you can use the view projection, which is passed to the loader as 3rd argument. Then you do not need to hard-code the projection.

Instead of spreading metadata across assets that the STAC layer group creates, I'd suggest making them available through the STAC instance (e.g. getBoundsLayer() instead of setting a bounds boolean on the layer. Same for the stac data, which should not be set on each feature.

Thanks, good pointers!

Switched to use a loader, which seems to work perfectly.

I removed the stac metadata for the features, this is not needed anymore (due to the change for STAC support (a STAC layer group) #14927 (comment)). I added a getBoundsLayer() method, but the metadata on the assets is still valuable due to the nesting of the LayerGroups, I think. In case you go through all layers, it is helpful to be able to retrieve the relevant STAC entities. Using that for example for customized LayerSwitcher or for the "click detection" in stacUtils / the STAC Item Collection example.

m-mohr · 2023-08-21T10:40:02Z

src/ol/source/GeoTIFF.js

@@ -382,7 +384,7 @@ class GeoTIFFSource extends DataTile {
    super({
      state: 'loading',
      tileGrid: null,
-      projection: null,
+      projection: options.projection || null,


I've extracted the changes in this file to #15036 so that we could also release this PR separately, if required.

m-mohr · 2023-08-21T10:55:00Z

src/ol/events/ErrorEvent.js

@@ -0,0 +1,25 @@
+/**


This was a shared event between MapboxVector and STAC, but now that MapboxVector was removed I could also keep it outside of the events folder and copy it into stacUtils.js or STAC.js. Whatever you prefer.

m-mohr · 2023-08-22T01:58:13Z

Hey there,
to be able to get this into our projects via npm etc, I (temporarily?) released this in a separate repo: https://m-mohr.github.io/ol-stac/
I used the OL repo as a template with all the nice boilerplate for website, examples, docs etc. I'm wondering if this is fine with you/the OL maintainers? Shall I change the design more to make it look too less like an "official" openlayers thing?

ahocevar · 2023-08-22T06:52:29Z

Thanks @m-mohr for your effort on this, and having this as a separate library makes perfect sense! No objections from me on how the website looks.

Would you mind creating a pull request that adds your library to the list of 3rd party libraries in site/src/3rd-party/index.hbs?

Also, to make this more prominent in OpenLayers, I think it would be nice to have an example here that uses your library.

m-mohr · 2023-08-22T14:31:02Z

Thanks, @ahocevar. If you still want STAC be part of OL, I'm also happy to also have it live in OpenLayers directly. Up to the maintainers :-) But I wanted to get this out so people can start using it and give feedback.

Would you mind creating a pull request that adds your library to the list of 3rd party libraries in site/src/3rd-party/index.hbs?

Sure, see #15041

Also, to make this more prominent in OpenLayers, I think it would be nice to have an example here that uses your library.

I tried this, but couldn't figure out how it works with the dependencies. How can I reference external dependencies? If I just add the ol-stac import, it can't resolve it. Any hints? devDependencies? See #15042

m-mohr changed the title ~~Stac js~~ STAC support (a STAC source and layer group) Jul 20, 2023

m-mohr force-pushed the stac-js branch from 9e98fb8 to 95619db Compare July 20, 2023 20:38

m-mohr changed the title ~~STAC support (a STAC source and layer group)~~ STAC support (a STAC layer group) Jul 21, 2023

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m-mohr marked this pull request as ready for review August 2, 2023 16:43

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m-mohr added a commit to tschaub/openlayers that referenced this pull request Aug 21, 2023

Allow to set GeoTiff projection openlayers#14663 openlayers#14927

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Allow to set GeoTiff projection #15036

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Add a STAC LayerGroup

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Add OL STAC to 3rd party page #15041

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STAC support (a STAC layer group) #14927

STAC support (a STAC layer group) #14927

m-mohr commented Jul 20, 2023 •

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STAC support (a STAC layer group) #14927

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STAC support (a STAC layer group) #14927

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