Migrating from PostGIS 1.5 to 3.2: need to replace geography_typmod_dims

Question

I can't find a replacement function for geography_typmod_dims which is used in an old application.

In 1.5 there were: geography_typmod_dims, _in, _out, _srid and _type.

In 3.2 I find only: geography_typmod_in and _out.

Answer 1

Here is an old example showing geography_typmod_dims being used to get the coordinate dimensions of a field from the pg_attribute typmod for the field. That is being used to create the coord_dimension field in the postgis.geography_columns view.

Current PostGIS support for geography designates dimensions using M, Z or ZM suffixes on type names.

CREATE TABLE test (
  blank geography(POINT, 4326),
  m     geography(POINTM, 4326),
  z     geography(POINTZ, 4326),
  zm    geography(POINTZM, 4326)
);

db=> SELECT f_table_name, f_geography_column,
            coord_dimension, type
     FROM geography_columns;
 f_table_name | f_geography_column | coord_dimension |  type   
--------------+--------------------+-----------------+---------
 test         | blank              |               2 | Point
 test         | m                  |               3 | PointM
 test         | z                  |               3 | PointZ
 test         | zm                 |               4 | PointZM
(4 rows)

You should be able to replace uses of geography_typmod_dims one of two ways:

1. If you know the table and column you are dealing with, look it up in the coord_dimensions field of the geography_columns view.
2. If you need to check the dimensions of a geography object, perhaps you can check the return from ST_Summary for Z, M or ZM and figure out the cases that apply to your application. Looking at the PostGIS Function Support Matrix, ST_Summary is the only function I see that might help you for geography.