jiayuasu commented on code in PR #10981:
URL: https://github.com/apache/iceberg/pull/10981#discussion_r1724586515
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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:
> accepted forms or values for CRS and Edges
If we borrow the conclusion from Parquet Geometry proposal, then C,T,E
fields are the follows:
C is a string. Based on what I understand from this PR, @szehon-ho made this
field a required field, which is fine.
T is optional and a string. Currently, it only allows this value `PROJJSON`.
When it is not provided, it defaults to `PROJJSON` too.
E is a string. The only allowed value is `PLANAR` in this phase. Based on
what I understand from this PR, @szehon-ho made this field a required field,
which is fine. @szehon-ho According to our meeting with Snowflake, I think
maybe we can allow `SPHERICAL` too? We can add in the spec that: currently it
is unsafe to perform partition transform / bounding box filtering when E =
`SPHERICAL` because they are built based on `PLANAR` edges. It is the reader's
responsibility to decide if they want to use partition transform / bounding box
filtering.
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