GIS buffer value degree to meters with spatiallite

Question

I am new to Spatialite. I have following query:

select A.* 
from linka as A, pointa as B 
where Contains(Buffer(B.Geometry, 100), A.Geometry)

I actually want to create 100 meters buffer and get to know which are the link's are contained by it.

I can able to find the inserted '100' is actually degree value and it's giving me output which are coming in this range.

I can put the degree value also in my query but the transformation from degree to meters/kilometers is not same all around the world. I gone through many sites and able to know 1 degree = 110 KM approx. but from GIS expert and some reference sites also get to know at each pole on earth it's different.

For instance, the difference at Alta/Norway between metrical x and y for planar approximation is 34 km in x direction equal 111 km in y direction. The buffer looks similar to this while using geographic coordinates:
http://extremelysatisfactorytotalitarianism.com/blog/wp-content/uploads/2010/08/tissot_indicatrix_equirectangular_proj.png

I build software which convert geographical data to geometrical (X, Y -coordinate format) data and make transformation where Spatiallite can understand.

I also trying to read regarding SRID things but not able to understand how to insert it into my query.

Answer 1

temporary transform your geometry to a metric projection (eg UTM) if i assume your current projection is WGS84 try the following statment

 transform (buffer (transform (B.geometry, #projection), #dist), 4326))

-in #projection: your new projection, eg: 32631 for WGS 84 / UTM zone 31N (choose the projection that fits your Zone)

-in #dist: distance in meters

(4326 for WGS84)

Answer 2

If You are using SQL server 2008 or later, You should be able to use spatial types

1. lets assume linka contains geography column, and its name is geo, and it contains Points
2. dont forget to create spatial index !

3. try this

   DECLARE @buffer geography = geography::Point( 1.234, 5.678, 4326 ); DECLARE @distance float = 100.0;

   SELECT * from linka WHERE linka.geo.STDistance(@buffer) < @distance