Fig.grdimage transparency and plot UTM

Q&A PyGMT Q&A
1

Hi all

I’m recently using PyGMT for my work and i got some issue for plotting raster image (.tiff) file. I got 2 problems here:

  1. grdimage didnt work when i used I (shading) and Q (NaN_transparent). I got this following error : grdimage [ERROR]: Option -Q: Cannot specify a transparent color for grids when intensities are also used
    And when i only used -I the background of the map was colored grey
  2. the file used UTM 54N projection and the result when i run the program I got this following error: “grdview [ERROR]: Map region exceeds 360 degrees”

I would greatly appreciate any advice or solutions from the GMT community.

Thanks you

2

Hi @rasta.2206

I think this problem was recently fixed (Grdimage transparency of NAN values). You will have to use the dev version.

For your second problem, I will need to see your script to help you.

3

Hi @Esteban82 thank for the answer
Sorry I still dont get it. What do you meant by using the dev version?
For my second problem this is my code

import pygmt
trench='D:/00_Pygmt/00_project/01_test/Mariana_PD19MT02_75m_geo.tif'
region = [351487.5, 1066612.5, 1182262.5, 1448587.5]

mariana_trench=pygmt.Figure()

mariana_trench.basemap(
    projection="U52N/15c",
    region=region,
    frame=["WSNE", "xaf", "yaf"], 
    )
mariana_trench.grdimage(
    grid=trench,
    cmap="jet",
    region=region,
    shading=True,)
   
    
mariana_trench.show()

Thanks

4

I meant to that you try to work with the development version of GMT. For that, you have to build GMT from source. What GMT version do you have?

5

I suspect that this image is already in UTM coordinates. If so, then, you have to use linear projection to plot the image correctly. Try adding using this instead:

mariana_trench.grdimage(
    projection=X15c
    grid=trench,
    cmap="jet",
    region=region,
    shading=True,)
6

Posting the example code that errors in pure GMT CLI is highly preferable.

7

I use GMT version 6.5.0
In development version the -I dan -Q parameters can work in the same time?

8

Ok thanks, it worked but the map looked distorted.

This one used plotted using UTM coordinates from the original file that using UTM projection.
Screenshot 2025-01-23 075717

And this one plotted using Geographic coordinates. This one I reprojected the image from the original.
Screenshot 2025-01-23 075637

Thanks

9

This is expected with projection=X15c. It sets both vertical and horizontal map size to the same value, 15 cm, regardless of the actual grid dimentions.

10

Yes, I forgot about that. Sorry.

In order to keep the original aspect, try using this command instead:
projection=X15c/0

11

No need to be sorry. This gave the topic starter opportunity to learn how X projection specification works.