On 26 March 2010 09:01, M.E.Dodd <[email protected]> wrote:
> Is it possible to find the nearest point in one table compared to points in
> another table BUT without using the same point in the second table more than
> once.
> I have one table of points and want to find the nearest point in another
> table, the trouble is that some points in the second table are used many
> times and others are not used at all even though they are only slightly
> further away. There are different numbers of points in each table, each
> table has hundreds or thousands of points. The multiple use of points in the
> second table like this might be biasing the analysis.
This is slightly complicated to determine. There are two tables A and
B, where the number of points in A is less than or equal to B. There
is exactly 1 solution, unless there are more than 1 set of points with
the same nearest-distance.
You will need to write some code up in R, PL/pgSQL, or any computer
environment with loops. Here is the pseudocode for the function:
Make an empty result set M for matches between A and B
While numrow(M) < numrow(A):
point A0 := Select any point A not in M order by x-coord, y-coord
point B1 := Find closest B point from point A0 not in M
point A1 := Find closest A point from point B1 not in M
Insert into M(A,B) values(A1, B1)
Return set M
-Mike
_______________________________________________
Qgis-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-user
