Making a vertical exaggerated grid

We all know how an exaggerated vertical scale often makes it easier to read a map, and usually more interesting to look at. This is a pure visual thing; you don’t do anything with the actual grid, but is this possible?

If I would like to manipulate my grid, so that a vertical exaggeration was ‘baked into it’, how would it be done? Is it possible?

@Andreas you did not say what kind of grid you wanted to exaggerate, but I assume you mean a topographic grid. An easy way to manipulate a topographic grid would be to use grdmath. In classic mode, you can use gmt grdmath topo.grd 10 MUL = topo_exag10.grd to multiply all the values by a factor of 10 (which is a large vertical exaggeration).

Thanks for the reply!

Yes, it’s a normal topographic grid. I think I tried your suggestion once, but it didn’t enhance the features I was looking for as much as I wanted to. I will try again though.

Maybe an algorithm to enhance small features/structures more than larger ones would be an idea. How to achieve this, I do not know.

Thanks again!

Just jack up the scale in grdgradient. Derivatives amplify small-scale features.

Paul, any way to bake this into my original grid?

A concrete example of this would be to exaggerate features (potentially small) in a grid, and then use the new -T feature in grd2xyz to print a 3D model.

Not sure how that would work. Let’s say you have a set of small hills that are 100 m tall and 10 km long, in an area that also have mountains that are 2000 m tall and 100 km long. You could imagine taking a Fourier transform and then increase the amplitudes of the shorter wavelengths (this is what grdgradient does in effect (but without FFT)) but a plot of such topography would probably look really strange as even those large mountains will have components that fall into your smaller scales and thus get magnified too.

If what you want to highlight is geographically restricted (just an area of a larger map) then the above would not work at all since it is a global method. Perhaps using a custom CPT for the area or z-range you are interested to highlight features. Hard to know what else to suggest without a specific case so we can understand exactly what features you may be talking about.

Thanks for input and help.

Making a custom CPT for the area or z-range is difficult because I don’t know where they are :slight_smile:

This is a bathymetric (or hypsometric…?) grid where I’m trying to find mounds and heights, typically sub/semicircular in apperance with a radius of 10-20-30 meter. How to filter out the noise…

In what area? Maybe a slope map can help you.

Thanks Esteban82.

It’s in the mid-atlantic rift. Very small features which requires high res bathymetry.