[GRASS-user] How to find intersection of two lines

[Jarek Jasiewicz]

Moritz Lennert wrote:
> On 20/03/08 17:15, Jarek Jasiewicz wrote:
>> Moritz Lennert wrote:
>>> On 20/03/08 11:17, Jarosław Jasiewicz wrote:
>>>> Hi I have lots of raster, thinned lines and second raster with with 
>>>> one line. I must find all points where second line intersect with 
>>>> lines on first raster
>>>> it is very simple:
>>>>
>>>> r.mapcalc points=if(raster_two==1&&raster_one==1,1,null())
>>>>
>>>> but there is one exception:
>>>>
>>>> AB
>>>> BA
>>>>
>>>> when lines intersect with 45 grades. There is intersection but 
>>>> without common point. Naither buffor nor grow is not a solution 
>>>> because I need exactly one point lying exactly on line from raster one
>>>>
>>>> Any Ideas
>>>
>>> Either ressample your rasters to coarser resolution to make them 
>>> coincide, or convert to vector and use a combination of v.patch + 
>>> v.clean (e.g. v.clean input=lines1 output=lines2 err=points tool=break)
>>>
>>> Moritz
>> thanks for ansfer
>> I tried it with similar way (v.patch +v.clean + topology report) but 
>> it is not it. I need EXACT coordinates of pixels on intersection do 
>> to transfer it to another program
>
> The map points (created with the parameter err=points) should contain 
> exactly these points. Obviously this only works if you can create 
> correct vector lines from your raster.
>
> See example here:
> http://geog-pc40.ulb.ac.be/grass/misc/intersections.html
>
> Moritz
yes, but real (single prescision) coordinates of the point are not exact 
of coordinates of pixel,

for example:
point: x=3567891.36345671, y=x=6564456.8176236
pixel: x=3567891.36357892, y=x=6564456.8339658

but, v.to.rast and r.to.vect solve that problem


Thanks for help

Btw: theat is nice method of find point of intersection of lines, better 
than topology report