How to use ST_Length?

Question

I want to calculate the lenght of the line inside the polygon.

If I do this:

SELECT ST_Length(ST_Intersection(ST_Transform('SRID=3035;LINESTRING(4000000 3000000, 
                                                                    4005000 3005000)',
                                 4326),
                                 ST_Transform('SRID=3035;POLYGON((4000000          3000000
                                                                 (4000000 + 5000)  3000000,
                                                                 (4000000 + 5000) (3000000 + 5000),
                                                                  4000000         (3000000 + 5000),
                                                                  4000000          3000000 ))',
                                4326)))

I get as a result: 0.0809729885483392

Shouldn't I get around 7000? What am I doing wrong?

Answer 1

You transformed to SRID 4326 which uses the unit degrees. That's why your result is so small. Why do you transform?