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benbovy / spherely

Manipulation and analysis of geometric objects on the sphere.
https://spherely.readthedocs.io/
BSD 3-Clause "New" or "Revised" License
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Dimension property: returned value for geography collections #57

Open benbovy opened 1 month ago

benbovy commented 1 month ago

In the case where a collection contains features of different dimensions, the default value returned via s2geography (-1) is not consistent with the value returned by shapely (max dimension value found).

Which one do we want?

_Originally posted by @jorisvandenbossche in https://github.com/benbovy/spherely/pull/51#discussion_r1806473111_

jorisvandenbossche commented 1 month ago

I am not entirely sure why s2geography returns -1 (cc @paleolimbot?), because AFAIK R's s2 returns the max dimension of the parts (except for an empty collection): https://r-spatial.github.io/s2/reference/s2_is_collection.html (see the examples). And I suppose this is then also consistent with bigquery (I assume, based on the description, but didn't test that)

jorisvandenbossche commented 1 month ago

It seems that in s2geography, there is a difference between the Geography::dimension() attribute and the s2_dimension() function.

The attribute is used in code where you want to know if you have points or polylines or polygons (and if not one of those three, it returns -1), and then the logic to calculate the max dimension in case of collections is handled inside the s2_dimension function (https://github.com/paleolimbot/s2geography/blob/1c67ddc62c30977fabca291fb68fd8cb62f3beaa/src/s2geography/accessors.cc#L55-L69)