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https://issues.apache.org/jira/browse/CALCITE-2031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16236263#comment-16236263
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Julian Hyde commented on CALCITE-2031:
--------------------------------------
You can often find good, simple examples that can be turned into test cases on
the PostGIS site; for example [ST_X at
PostGIS|https://postgis.net/docs/ST_X.html].
[H2GIS|http://www.h2gis.org/docs/dev/functions/] also has good documentation,
for example [ST_X at H2GIS|http://www.h2gis.org/docs/dev/ST_X/], but you *must
not copy-paste examples from H2GIS* because the license is not compatible with
Apache.
> Implement more OpenGIS functions
> --------------------------------
>
> Key: CALCITE-2031
> URL: https://issues.apache.org/jira/browse/CALCITE-2031
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> The initial set of OpenGIS functions were implemented in CALCITE-1968 but
> there are quite a few more to implement.
> Each function can be implemented separately, and with very little effort: you
> typically need to find the commented function in in
> {{[spatial.iq|https://github.com/apache/calcite/blob/master/core/src/test/resources/sql/spatial.iq]}}
> (it will be followed by the comment {{# Not implemented}}), add one or two
> queries as test case, add a method to {{GeoFunctions.java}}, iterate until
> the test cases work, then add a row to one of the tables in {{reference.md}}
> to document that the function is now implemented.
> I suggest that each pull request implements a few related functions. A good
> place to start would be {{ST_X(geom)}}; {{ST_Z(geom)}} is very similar and is
> already implemented.
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