title: Calculate point distance in postgis/postgresql
body: <p>I am trying to calculate the distances between points in PostgreSQL, and now I have the longitude and latitude value for each point, and I know it's from GPS(WGS84).</p>
  
  <p>Because all the points are in same city, and not very far from each other, so I know that use geometry with a local cartesian projection is better, because compared with using geography, it needs less calculation.</p>
  
  <p>My question is how can I find the suitable cartesian projection for my data? If I can find one, is it the SRID value which should be used in <code>ST_Transform</code>?</p>
  
  <p>Thank you very much!</p>