I'm trying to remove inner polygons with postgis. I've created a routine, that resumes in:
From a polygon table, with a unique id:
- Create a linestring table from polygon
- Import to postgis
- Get the length of each line
Now I have a table with, for example, 5 linestrings for each id, each linestring was a polygon, and I want to get ONLY the longest line from each ID.
For this, I have a select, but I don't know how to group the geometry, to get ONLY the longest line
select id, geom as length from esp_lines group by id
I have to group it by another field, but I don't know which one.
The other solution I've found is:
select id, max(geom) as length from esp_lines group by id
but max(geom) doesn't give me the expected result (the longest linestring)
Does anybody know if is there any function to get the longest linestring of a group?