Thanks Brent, I think I understand GIS a little bit now ...
Just two more questions,
1. When looking for points within a circle, is this the recommended way?
Which is,
Storing data in `location geometry(point, 4326)` , convert it to
geography then do the calculation
2. I tried to create
Hi,
I've been searching online for days. Trying to understand why SRID is
required. So I picked some random value.
Now I'm need to retrieve POINTs within a circle range, e.g a circle at
(146.0, 138.19) with radius of 100 meters:
SELECT * FROM users
WHERE ST_DWithin (users.location,
Hi Aaron,
SRID is used to set a consistent coordinate system to the data. It refers
to an EPSG Coordinate Reference System (CRS). For instance, EPSG:2600: (
http://spatialreference.org/ref/epsg/2600/) is a metric CRS.
Coordinates (146.0, 138.19) are not valid in SRID 2600 (nor in lat/long
Hey,
I would sugger to read a little bit about geographical information
https://en.wikipedia.org/wiki/Spatial_reference_system before using
PostGIS.
The unit depend on the way you measure, which depends on the Spatial
Reference System.
If you want it is a bit like measuring the temperature in
Hi Aaron,
Hopefully this (simplistic) description helps.
Setting a SRID value for a feature tells Postgis what coordinate reference
system (CRS) the coordinates are in. This includes the unit, which can be any
linear unit of measurement, such as degrees (measured at the surface of the
earth),
In terms of the efficiencies underlying the query - I don't know enough to
advise you. there are a few ways to phrase such a query, I don't know the
advantages/disadvantages. My guess is that using 2D geometrires will be faster
than 3D geographies - but the casting of lon/lat coord geometries
