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I'm a new to GIS and I'm trying to develop an optimal path across an area by using GRASS 7 features.

It is very similar to the task given here.

The problem is that I don't have any data with elevation points and cost surface for this area.

How can I create a raster with the cells showing low-high travel costs and how can I set an elevation points?

  • first describe the 'area' you're trying to develop an optimum path across... is it sidewalks? roads? bike lanes? lowest elevation? lowest slope? – DPSSpatial Aug 5 '15 at 21:46
  • It's a lake. So I don't have anything like road network or etc. All I need is to set a high-cost area alongside the coastline (I guess). – AdamJ Aug 6 '15 at 0:39
  • Just to clarify the subject. I need to develop an optimal path (accordind to minimum length) through the lake between two points. The one main condition is that path can't lay too close to the coastline. – AdamJ Aug 6 '15 at 13:28
  • So you would start out with a polygon for the lake? A cost surface for the lake and the coastline would involve creating two rasters - 1 for the lake and the values would all be low (1), and the outline of the lake converted to raster, given a high cost (10), then merged with the lake raster. Now you have a single raster or cost surface that you can use for point to point cost path calculations. Routes would avoid the coastline (high cost), but otherwise would pretty much go in a straight line between the two points. Does that sound like where you want to go with this? – DPSSpatial Aug 6 '15 at 15:22
  • Exactly! Thank you very much! Was thinking about something like that but wasn't sure. Just one more question. So, I need to create new polygon for outline of the lake (for example) > go to attribute table manager > add column with '10' value > then convert to raster using this column as source for values > merge with other layers. Did I get it right? – AdamJ Aug 6 '15 at 16:20
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How I solved my problem:

  1. Firstly, vectors of required 'cost areas' were created (was trying to do it in GRASS but it's too painful - ended up in QGIS).
  2. Then I set appropriate cost values for each of such 'cost area' vectors (by this point I was already working in GRASS; we set cost values by adding new column in the attribute table of each vector then fill it with appropriate values [low(1)-high(10)]).
  3. Convert each vector layer to raster using created column with given cost values as a source for raster values.
  4. Merge received raster layers.
    • just to be sure that everything is OK with raster values I made a reclassification (r.reclass module).

After all, it is pretty easy to create a simple cost surface.

This now works perfectly in my project with help from mapBaker.

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