Slopefile with high values

Q&A
1

  1. When I made a slopefile with grdgradient -Sslopefile, of a bathymetric grid, my maximum values were above 9 rad. How is this possible? A sloping plane can have maximum a value of 90 deg (= \frac{\pi}{2} rad)!?

  2. When I converted this grid containing rad, to deg, with grdmath ATAND, it correctly converts to sensible deg values; I think the maximum values I got were 84 deg-something. This seems reasonable. Why does ~ 9 rad equal ~ 84 deg?

2

Hi Andreas,

The grdgradient program output is not in radians, but in meters/meter (assuming your data is in meters) that is the tangent of the slope angle. That is why using the ATAND program converts it to slope in degrees.

3

Here there is an example on how to make a slope map with GMT.

4

Thank you both!