title: ST_DWithin takes parameter as degree , not meters , why?
body: <p>The <a href="http://postgis.org/documentation/manual-svn/ST_DWithin.html">ST_DWithin</a> document says , the third parameter(distance) is in meters. But when I execute some query , it seems it takes the 3rd parameter as 'degree' ?</p>
  
  <p>Here is my simplified table structure :</p>
  
  <pre><code>&gt; \d+ theuser;
                           Table "public.theuser"
    Column  |          Type          | Modifiers | Storage  | Description 
  ----------+------------------------+-----------+----------+-------------
   id       | bigint                 | not null  | plain    | 
   point    | geometry               |           | main     | 
  Indexes:
      "theuser_pkey" PRIMARY KEY, btree (id)
      "point_index" gist (point)
  Referenced by:
      ...
  Has OIDs: no
  </code></pre>
  
  <p>All points are stored with SRID=4326.</p>
  
  <p>And this is the query :</p>
  
  <pre><code>&gt; select * from theuser where ST_DWithin(point , ST_GeomFromText('POINT(120.9982 24.788)',4326) , 100 );
  </code></pre>
  
  <p>It takes the 3rd parameter (100) as 'degree' , so it returns all data , I have to narrow down to 0.001 to find nearby points.</p>
  
  <p>But how do I directly pass meters as 3rd parameter (I don't want to do meter/degree transformation ) ? What's wrong with my query ? why postgreSQL doesn't take it as meters as document says ?</p>
  
  <p>Environments :</p>
  
  <pre><code>&gt; select version();
                                                    version                                                  
  -----------------------------------------------------------------------------------------------------------
   PostgreSQL 8.4.9 on i486-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu 4.4.3-4ubuntu5) 4.4.3, 32-bit
  
  &gt; SELECT postgis_lib_version();
   postgis_lib_version 
  ---------------------
   1.4.0
  </code></pre>
  
  <p>If it is the SRID that causes this problem , what SRID directly makes use of 'meter' as the unit ? (I tried transforming to SRID=2163 , but still in degree) Thanks.</p>