When Drape an image to grid,the cloud on image become strange

When drape this image to grid:

this is result:

note that the cloud become colorful,why how to solve it ,Thanks!

This is the data and gmt script:


1 Like

I solved it:
use grdgradient and set -N to e0.2 or less.

Hi Mark,

That is really neat. I did not know that trick before (the image drape thing).

my question is,m how did you make the Google Earth image geo-referenced? When I save imaged out of Google earth they don’t have spatial information.

Also, in your solution, did you run grdgradient on the ‘image.png’ file then write that out to another grid that gets draped on the terrain data?



If you want to drape images over topography you should use grdview

If you want drap an image,the image itself doesn’t need any georeference at all.

Ah, i see, thanks for info.

Downloading referenced images with Mirone is trivial.A slightly outdated how-to

When you add illumination ofc it changes the colors provided in by the draping image.

Just a test,I know it’s not precise.

Joaquim,Is there a way to apply illumination to a draped image?

You applied illumination in your first example. But illumination can only be applied to grids, not images.

Joaquim,sorry for long time , I suddenly recalled this:
( I do applied illumination on grid file,but the gird which is draped an image)
The second picture above is a grid which draped an image ,and also applied illumination on it,
The only odd thing is that the white color in that image will become colorful,and the remain is normal,but aplly illumination on draped grid is an normal operation on other GIS software,Is somthing wrong in here?

When I have time to look at the grdblend I’ll look a this again. But quickly, you are mixing two color info. One is the shading and the other is the color from the draping image so colors have to change.

I still haven’t got the answer,so I drew it to make my expression more explicitly:

If you shade and drape the draping color will be changed. No way around that and the other GIS softwares, if they do this operation, will come out with the same result.
And certainly the algorithm is not seeking for the white colors to change only them. It happens that the effect is more visible there.

That’s means I can’t apply illumination on a draped image,Is that right?
But I applied the image as a texture in global mapper,and that is the result:

The color is all good,I was confused!

No color changed and also applied illumiantion :

Right, the clouds are not so reddish (but still a tiny bit) but on the other hand they nearly disappeared and the image is clearly darker.

This is what I get with another software (Mirone) and a slightly more cloudy image.
And, BTW, in your grid the sea is at 65/66 meters high.

Joaquim, yesterday I checked the command and do a little change ,and the result became pretty good,here it is:

Another view:

And there is no strange color.
The right color command:

set “in_grids=origin.grd”
set “light_grids=origin.grd.light”
set “range=167.88/168.36/-16.39/-16.08”
gmt grdview %in_grids% -R%in_grids% -JM15c -JZ1.5c -Qi1000 -I%light_grids% -Gimage.png -p135/25+w168.12/-16.235

The former command:

gmt grdview origin.grd -R167.84/168.40/-16.42/-16.06 -JM15c -JZ0.5c -Qi1000 -I+d -Gimage.png -p180/90

It seemed the default illumination’s problem which generated by GMT.