grdgradient -S says: Name of output grid file with scalar magnitudes of gradient vectors.
Does this mean that output is in radians?
grdgradient -S says: Name of output grid file with scalar magnitudes of gradient vectors.
Does this mean that output is in radians?
No. Gradient magnitude is in z-data-units/horizontal distance.
Thanks Paul.
So in order to get the degree of slope, I could take arctan(z-data-units/horizontal distance)
(based on this)?
Are there any gmt-utilities that can do this for me directly, or do I have to use some grdmath
RPN magic?
So slope only makes sense for DEMs. For other data types there is no āangleā, just things like mGal/km. If you converted to flat Earth scaling (via -fg) then I think the gradients for a DEM will be in meters/km and you would need to scale it by 0.001 to get dimensionless tangents and then inverse tangent to get the angle.
Try this to get a slope grid in degrees.
gmt grdmath $GRD ATAND = $SLP
grdgdal
says it can do it.
-A prog[+m method +c cpt]
Select which GDAL program to run (currently one of info, dem, grid, rasterize, translate or warp). When program is dem then please append +m method (pick one of hillshade, color-relief, slope, TRI, TPI or roughness)
Thank you all for tips and comments. Will test.
grdgradient
; is the gradient that is computed the same as the gradient in physics? So (upside down triangle, del, ā)(x,y,z)? Partial derivatives? In deep water hereā¦Mmm note sure, but I would say that it is not neccerary.
Yes, the gradient is the vector i * dz/dx + j * dz/dy where i and j are the unit vectors in the x and y directions. Then the magnitude of this vector is reported by grdgradient and its direction via -S.