topic Re: line clip or segment by adjacent polygon in Spatial Data Science Questions

line clip or segment by adjacent polygon

youngpark — Sun, 03 Jun 2018 07:22:17 GMT

Hello.

I am trying to clip or create split lines by an adjacent polygon. if you see the attached image, the line is a river and the polygon is some property. I would like to cut the line as marked yellow. if you have a good idea please let me know.

I was thinking about left or right buffer and mask it. I think there are a better idea for that.

Thanks,

Re: line clip or segment by adjacent polygon

DanPatterson_Retired — Sun, 03 Jun 2018 11:39:58 GMT

Do it manually.

A buffer will extend in all directions and won't buffer exactly where you want to anyway.

If you have many polygons, you will end up with a mess of little pieces where overlapping buffers intersect

Have you got an image where you tried the buffering approach?

Re: line clip or segment by adjacent polygon

youngpark — Sun, 03 Jun 2018 13:21:53 GMT

Dan,

So far, it wont do 100 percent accurate. But it does some work. my procedure is as follows.

1. create polygons' features extent on an attribute table.. min x, min Y, max x, max Y

2. create two lines per polygon features.

3. select longest one between two lines

4. buffer from the line segments to clip river line.

5.,,,,

if you have a better idea... pls, let me know.

thanks,

Re: line clip or segment by adjacent polygon

DanPatterson_Retired — Sun, 03 Jun 2018 14:55:28 GMT

The extent thing seems plausible since it would enable you to readjust if you converted the extent polygon to a polyline and used if for the splitting.

A couple of other visual examples might help

Re: line clip or segment by adjacent polygon

DuncanHornby — Fri, 08 Jun 2018 09:57:20 GMT

Another approach could be this:

Explode the pink polygon into it's vertices
Snap all these points along your river network
From these snapped points Identify the nearest and furthest away point from the river mouth. You now have a pair of points which would be the start/end of the line you want to create. You would want to remove all the points between. Passing distance to mouth to all the points would allow you to achieve the dropping of unwanted points by polygon ID.
Trace along your river network between these two points to create the routes you require.

Your image throws up a problem that you will have to deal with and that is tributary junctions, so tracing in my mind is the only option.

RivEX can do all but step 1 (there is a geoprocessing tool for that), you'll need to do some data processing then you could use the link tool searching for nearest upstream site. As you may have multiple property polygons along a single river the link tool will generate routes to u/s points which you may not desire (but you could easily remove those). Also this approach works if you never have properties on opposite sides of the river facing each other as that would create overlapping routes.