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I'm working on a 15*10 km area, splatted in a 50*50 m cell grid. I want to compute the time needed to travel from a single starting point to each cell centroid, combining driving and walking time.

I placed a point every 30 m along my trail/roads. Using pgrouting,I already have the least time cost from my single startpoint to each of these points.

I computed the shortest path of each centroid to the nearest trail/road point. Assuming the same point-centroid walking speed (4 km/h), I get a time for each. I had first used the "Walking time" extension on those segments, but some times weren't realistic (canyons).

nearest nodes

But the time costs limits are raw on the raster: the nearest point on the road/trail isn't necessarily the fastest.

Roads/hiking trails and total time raster. As you can see, there are raw limits in time costs

Beside that, this approach doesn't take into account the slope, I tried r.walk and r.drain, but I can't figure out how to use it with all this : there are over 4 000 roads/trails nodes and 27 000 centroids !

How can I get the least-cost path from any of the centroid to the fastest trail/road point ?

I'm using Qgis and Grass.

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