Distance between 2 POINTs in Postgis in srid 4326 in metres

Question

This is probably a simple question, but I\'m not very good at PostGIS and don\'t fully grok all of this.

Basically I have a table (nodes) with a POINT colum

Answer 1

You could use ST_Transform to use meters, also remeber that not all functions are available with geography types but if you really need speed use ST_DWithin, is the fastest way. Here's an aproximation of conversions between degrees and meters:

| places | degrees    | distance |
| ------ | ---------- | -------- |
| 0      | 1.0        | 111 km   |
| 1      | 0.1        | 11.1 km  |
| 2      | 0.01       | 1.11 km  |
| 3      | 0.001      | 111 m    |
| 4      | 0.0001     | 11.1 m   |
| 5      | 0.00001    | 1.11 m   |
| 6      | 0.000001   | 0.111 m  |
| 7      | 0.0000001  | 1.11 cm  |
| 8      | 0.00000001 | 1.11 mm  |

Answer 2

Old question but you just have to cast like this: ST_Distance(p.geom::geography, u.geom::geography) where p and u are alias for two tables

Answer 3

Since writing this, I have discovered the "geographic" as opposed to the "geometry" type in PostGIS, which might do exactly what I want.