[Geometry] spatial linestring access along line
Hi all, before I begin, let me tell that geometry is not exactly my strong suite so please forgive my probably dumb question. I have started to work with boost geometry which, I find very neat, and assembled a line string. Now I basically need a method that gives me a point to a length value. Like when my linestring is 100 units long and I say give me the point at 3 I want the exact position of the point (coordinates) as if I were following the line for exactly 3 units. I have an approach that would allow me to implement this myself by following the segments (possibly after indexing them) but I have a feeling that one of those many functions provided by the library itself might do just that and I simply don't know it. If anyone knows if such is the case, would be nice to give me a heads up. Thanks, Stephan
Hi Stephan, On 23-5-2012 17:08, Stephan Menzel wrote:
Hi all,
before I begin, let me tell that geometry is not exactly my strong suite so please forgive my probably dumb question.
I have started to work with boost geometry which, I find very neat, and assembled a line string.
Now I basically need a method that gives me a point to a length value. Like when my linestring is 100 units long and I say give me the point at 3 I want the exact position of the point (coordinates) as if I were following the line for exactly 3 units.
I have an approach that would allow me to implement this myself by following the segments (possibly after indexing them) but I have a feeling that one of those many functions provided by the library itself might do just that and I simply don't know it. If anyone knows if such is the case, would be nice to give me a heads up.
There is no such function built in. You are probably looking for a function as LocateAlong, http://postgis.refractions.net/documentation/manual-2.0/ST_LocateAlong.html This function is (ever) planned, it is part of the OGC SF specification. But it is not there yet. Regards, Barend
Thanks Barend,
the function you mentioned is just what I needed.
I have implemented it on my own. Sadly, only the brute force approach
using for_each_segment and adding up the length travelled.
Great lib nonetheless.
Cheers,
Stephan
On Fri, May 25, 2012 at 1:14 PM, Barend Gehrels
There is no such function built in. You are probably looking for a function as LocateAlong, http://postgis.refractions.net/documentation/manual-2.0/ST_LocateAlong.html
This function is (ever) planned, it is part of the OGC SF specification. But it is not there yet.
Regards, Barend
participants (2)
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Barend Gehrels -
Stephan Menzel