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stac-extensions / perspective-imagery

Describes perspective imagery collected by photogrammetric or non-photogrammetric cameras
Apache License 2.0
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Default CRS for pers:crs #3

Open heidivanparys opened 2 years ago

heidivanparys commented 2 years ago

The default CRS is defined as EPSG:4326, however, the default CRS defined in OGC API - Features - Part 1: Core is http://www.opengis.net/def/crs/OGC/1.3/CRS84. This extension should probably use the same default CRS, for consistency reasons.

AsgerPetersen commented 2 years ago

This is closely related to the discussion in #2

heidivanparys commented 2 years ago

This is not really related to #2. The question is not whether to use URIs or not, the question is really about the default CRS.

For the OGC APIs, when the CRS is not explicitly given, it defaults to http://www.opengis.net/def/crs/OGC/1.3/CRS84 (in whatever format: OGC:CRS84, its PROJJSON description or its WKT description). In this extension, when the CRS is not explicitly given, it defaults to EPSG:4326. This is not consistent with the practice for OGC APIs, and may give interoperability issues, especially if/when the STAC standard, and possibly also extensions, will be brought into OGC.

m-mohr commented 2 years ago

I guess the main issue is that many people use OGC:CRS84 and EPSG:4326 interchangeably, because it is not clear what the difference is/they think it's the same?

Nevertheless, I think for this extension I don't see an issue. STAC spec and/or STAC API will be brought into OGC and they follow OGC. But the extensions will likely not be brought into OGC and as such they can choose the default that best fits their need. That doesn't mean that it may help to switch here, but it also doesn't seem like a major issue. Especially as EPSG:4326 is well-known and widely supported, while CRS84 still seems to be relatively new and less adopted...

cportele commented 2 years ago

OGC:CRS84 is not really new, it dates back to WMS 1.3, but indeed quite common to use EPSG:4326 and expect that others ignore the axis order in the CRS definition.

OGC standards are required to be explicit how they handle axis order. For example, GeoPackage explicitly ignores axis order in the CRS definition to be compatible with the use of WKB in practice, so EPSG:4326 means lon/lat. Others including GeoJSON accessed via an API implementing OGC API Features Part 2 require to use the axis order as stated in the CRS definition. So, OGC:CRS84 means lon/lat and EPSG:4326 means lat/lon.