jiayuasu commented on code in PR #10981:
URL: https://github.com/apache/iceberg/pull/10981#discussion_r1724561394
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format/spec.md:
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@@ -198,6 +199,9 @@ Notes:
- Timestamp values _with time zone_ represent a point in time: values are
stored as UTC and do not retain a source time zone (`2017-11-16 17:10:34 PST`
is stored/retrieved as `2017-11-17 01:10:34 UTC` and these values are
considered identical).
- Timestamp values _without time zone_ represent a date and time of day
regardless of zone: the time value is independent of zone adjustments
(`2017-11-16 17:10:34` is always retrieved as `2017-11-16 17:10:34`).
3. Character strings must be stored as UTF-8 encoded byte arrays.
+4. Coordinate Reference System, i.e. mapping of how coordinates refer to
precise locations on earth. Defaults to "OGC:CRS84". Fixed and cannot be
changed by schema evolution.
Review Comment:
@wgtmac We should add this value to the Parquet spec for sure. CC
@zhangfengcdt
@szehon-ho I think we should be more clear about the absence of CRS field
(inspired by the GeoParquet spec) if the CRS field is optional. `When the CRS
field is not provided, it assumes the data is in OGC:CRS84.`
There is another situation mentioned in the GeoParquet spec: `If the CRS
field presents but its value is null, it means the data is in unknown CRS`.
This situation happens sometimes because the writer somehow cannot find or lose
the CRS info. Do we want to support this?
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