# Tobler's hiking function on QGIS

I'm trying to apply Tobler's hiking function on QGIS using this formula:

(`your_res` / 1000) / (6 * 2.71828 ^ (-3.5 * abs ( Tan ( ( `your_slope`* 3.14159)/180) + .05)))

My DEM's resolution is 30m, and I have a slope layer in degrees (generated by the DEM layer in degrees before the re-projection). However, the resulting raster after applying the formula is 1 value useless layer.

I don't know where is my mistake exactly, all the youtube videos and the published articles are using ArcGIS.

Can it be done using QGIS?

## 1 Answer

It should work if your `Slope` values are `consistent`.

For the slope computation to be consistent, you need the original DEM to be reprojected in a CRS with `meter units`. Let's say you have a 30m resolution SRTM DEM (which comes as EPSG:4326), you first need to reproject it (Toolbox/Warp Reproject) to let's say (EPSG:3857)

In your formula, I am not sure why you would need the resolution part.

Following these steps in QGIS, pretty much what you mention, provides relevant results when slope are consistent (my sample DEM has almost vertical parts, with 80 degrees as the max slope)

• Thank you so much for your time and effort. I took the modified formula from an article osti.gov/pages/servlets/purl/1311302 P.8 additionally, he stated that the slope layer needs to be in degrees, but when generating such from the projected Dem, the slope will be in meters instead of degrees Following your steps, the results made more sense than before Commented Jan 10, 2023 at 13:40
• In arcgis path distance there is vertical factor, that makes it possible to use Tobler function. Algorithm accounts for all 8 possible directions from cell. Slope raster is irrelevant in this context. Commented Jan 10, 2023 at 21:22
• Then what is the nature of the calculated cost? if it's in hours, then the rough slopes (red areas) should have higher values and not the opposite Commented Jan 14, 2023 at 10:38