rdblue commented on code in PR #10981:
URL: https://github.com/apache/iceberg/pull/10981#discussion_r1907663335
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format/spec.md:
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@@ -205,13 +205,18 @@ Supported primitive types are defined in the table below.
Primitive types added
| | **`uuid`** | Universally unique identifiers
| Should use 16-byte fixed
|
| | **`fixed(L)`** | Fixed-length byte array of length L
|
|
| | **`binary`** | Arbitrary-length byte array
|
|
+| [v3](#version-3) | **`geometry(C)`** | Geometry features from [OGC – Simple
feature access](https://portal.ogc.org/files/?artifact_id=25355). Edges
interpolation is always linear/planar. See [Appendix
G](#appendix-g-geospatial-notes). Parameterized by crs C [4]. If not specified,
C is `OGC:CRS84`. | |
+| [v3](#version-3) | **`geography(C, A)`** | Geometry features from [OGC –
Simple feature access](https://portal.ogc.org/files/?artifact_id=25355). See
[Appendix G](#appendix-g-geospatial-notes). Parameterized by crs C[5] and
edge-interpolation algoritm A [6]. If not specified, C is `OGC:CRS84`. |
|
+
Notes:
1. 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`).
2. 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).
3. Character strings must be stored as UTF-8 encoded byte arrays.
-
+4. CRS (coordinate reference system) is a mapping of how coordinates refer to
locations on Earth. See [Appendix G](#appendix-g-geospatial-notes) for
specifying custom CRS. If this field is null (no custom crs provided), CRS
defaults to `OGC:CRS84`, which means the data must be stored in longitude,
latitude based on the WGS84 datum. Fixed and cannot be changed by schema
evolution.
+5. See [4]. This must be a geographic CRS, where longitudes are bound by
[-180, 180] and latitudes are bound by [-90, 90].
Review Comment:
Rather than referring to a note in a note, I would just add both to the
description. [4] clarifies what a CRS is and [5] puts restrictions on the ones
that are valid for `geography`.
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