wgtmac commented on code in PR #494:
URL: https://github.com/apache/parquet-format/pull/494#discussion_r2048270066
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Geospatial.md:
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@@ -104,6 +104,19 @@ crosses the antimeridian line. In geographic terminology,
the concepts of `xmin`
For `GEOGRAPHY` types, X and Y values are restricted to the canonical ranges of
[-180, 180] for X and [-90, 90] for Y.
+When `GeospatialStatistics` is present, writers must omit zmin and zmax if and
+only if there are zero non-NaN Z values in the column chunk, and must omit mmin
+and mmax if and only if there are zero non-NaN M values. The bounding box must
+be omitted entirely if and only if there are zero non-NaN X values or zero
+non-NaN Y values in the column chunk. If Z or M values are missing, the writer
+may still include a bounding box using only the available dimensions.
+
+Readers may interpret the absence of a bounding box, zmin/zmax, or mmin/mmax as
+an indication that all corresponding values are null, and may use this
+information to skip data during predicate evaluation. For example, a reader may
+skip a row group if the bounding box is absent, indicating that all X and Y
+coordinates are null.
Review Comment:
```thrift
struct ColumnMetaData {
5: required i64 num_values;
12: optional Statistics statistics;
}
struct Statistics {
3: optional i64 null_count;
}
```
I still think that `ColumnMetaData::num_values ==
ColumnMetaData::statistics.null_count` indicates (implicitly) that the bbox
should be empty. We need to fix the implementation of unknown sort order
instead of complicating the spec.
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