desruisseaux commented on code in PR #10981: URL: https://github.com/apache/iceberg/pull/10981#discussion_r1947060354
########## format/spec.md: ########## @@ -228,6 +230,30 @@ Notes: For details on how to serialize a schema to JSON, see Appendix C. +[1001]: <https://portal.ogc.org/files/?artifact_id=25355> "OGC Simple feature access" + +##### CRS + +For `geometry` and `geography` types, the parameter C refers to the CRS (coordinate reference system), a mapping of how coordinates refer to locations on Earth. + +The default CRS value `OGC:CRS84` means that the objects must be stored in longitude, latitude based on the WGS84 datum. + +Custom CRS values can be specified by a string of the format `type:identifier`, where `type` is one of the following values: + +* `srid`: [Spatial reference identifier](https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier), `identifier` is the SRID itself. Review Comment: > Does SRID:4326 mean EPSG:4326? Is it common to assume EPSG as the default authority for the codes? Not exactly. SRID usually means "the primary key in the context of those data". In a spatial database, this is the primary key of the `spatial_ref_sys` table. Theoretically, this is independent of EPSG codes. However, it is a common practice to use the same numerical values for convenience. For mapping SRID to EPSG code in a spatial database, we need to look at the other columns. If and only if the value of `AUTH_NAME` is `EPSG`, then the value of `AUTH_SRID` is the EPSG code. But we could also have the `IAU` value in the authority column, in which case the authority code is for some astronomical body (Moon, Mars, Jupiter, etc.). Note that even when `SRID` = 4326, `AUTH_NAME` = "EPSG" and `AUTH_SRID` = 4326, we do not really have "SRID:4326" = "EPSG:4326" because the authoritative definition of the latter has (latitude, longitude) axis order. Any other axis order is not EPSG:4326, but rather some derivative of EPSG:4326. Therefore, `SRID:4326` should rather be understood as "related to EPSG:4326" instead of "same as EPSG:4326". -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
