[GIS] How to split line at a specified distance and getting coordinates of start and end points of each line segment？

grasslineqgis

I tried v.split in GRASS：
enter image description here

and my notebook ran a lot of time but showed this error：bad allocation, then I click "OK", and got nothing.

Are there other ways to split lines？and I hope to get 2 new columns in the same shapefile about coordinates of start and end points of each line segment.

Best Answer

Which version of v.split are you using ?

from the GRASS Plugin
from the Sextante plugin

If you use the v.split from the GRASS Plugin, please read pp. 101-118 of the QGIS manual.

you are not working in QGIS but in GRASS GIS and the input layer and the output layer are GRASS layers and not shapefiles (t1.shp) or QGIS layers, see v.split.

v.split in GRASS GIS

If you want to use directly a QGIS layer and get a shapefile layer as result use one of the v.split from the Sextante Plugin (v.split.lenght and v.split.vert)

enter image description here

v.split.lenght with Sextante

You can also get the same result with Python and the Shapely module

Related Solutions

[GIS] Creating points in specified distance along line using QGIS？

There is now a plugin called QChainage that does exactly what you want. You specify an interval distance and the plugin creates points along your line at the specified interval.

[GIS] How to extract elevation values at line start and end points from a DEM

One of the easier ways to do this is with a spatial database such as PostGIS. Load your raster into the database using raster2pgsql (which is installed with PostGIS) and then load your rivers with shp2pgsql (also installed with PostGIS).

Then, you can run a simple query that samples the elevation model at the end points of all your lines:

select 
    st_value(r.rast, st_startpoint(geom)) as a, 
    st_value(s.rast, st_endpoint(geom)) as b 
from 
    rivers, dem r, dem s 
where 
    st_contains(st_convexhull(r.rast), st_startpoint(geom)) and      
    st_contains(st_convexhull(s.rast), st_endpoint(geom));

I've named the DEM twice in the from clause because the ends of the line may be contained by two different tiles in the raster, and each tile will have to be matched independently. That's why there are two st_contains calls.

The great thing about PostGIS is that you can automate this kind of processing over millions of records with a minimum of effort.

Note that this works if the line geometry is LineString. If they're MultiLineStrings, you'll have to refine the query, or use st_dump to turn them into LineStrings.

Best Answer

Related Solutions

[GIS] Creating points in specified distance along line using QGIS？

[GIS] How to extract elevation values at line start and end points from a DEM

Related Question