# How to plot DEM grid using -JG (perspective) projection?

**URL:** <https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759>\
**Category:** Q&A\
**Tags:** gmt\
**Created:** [April 1, 2024, 2:03pm UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759 "2024-04-01T14:03:30Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![gaiastucky](https://avatars.discourse-cdn.com/v4/letter/g/f475e1/32.png) [@gaiastucky](https://forum.generic-mapping-tools.org/u/gaiastucky)\
**Post date:** [April 1, 2024, 2:03pm UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759/1 "2024-04-01T14:03:30Z")

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Hi!

I am having some problems trying to use grdimage (or plotting a DEM) using -JG.

In past versions of GMT I have used the “-p” option in grdimage to make perspective plots with an overlain grid on my basemap.

However, this time, in GMT 6.5, I am making a plot that is similar-ish to  
[this example](https://docs.generic-mapping-tools.org/latest/gallery/ex26.html) (bottom one); so using the perspective projection “-JG” for a large slice of the planet.

Now, my script runs fine when I am just using ‘coast’ like the example shows

> PROJ=-JG${longitude}/${latitude}/12c+z${altitude}+a${azimuth}+t${tilt}+w${twist}+v${Width}/${Height}  
> gmt basemap $PROJ -Rg -BESnw+gslategray -By10g5 -Ba20xg10  
> gmt coast $PROJ -By10g5 -Ba20xg10 -Glightbrown -Slightblue -W -Ia/blue -Di -Na -Rg

But when I try to switch ‘coast’ to a grid being displayed (specifically the DEM of Mars which is what need to be plotting):

> gmt grdimage ./grids/mars\_dem.tif -C’matlab/copper’ -t35 -I+a-45+nt0.5+m0

I get the following error:

> grdimage [ERROR]: gmt\_gdalread: Computed -srcwin falls outside raster size of 720x360 in the x-direction.  
> grdimage [ERROR]: ERROR reading file with gdalread.  
> grdimage (gmtapi\_import\_grid): Could not open file [./grids/mars\_dem.tif]  
> [Session gmt (0)]: Error returned from GMT API: GMT\_GRID\_READ\_ERROR (18)

By the way, when I add some points using gmt plot, it also works perfectly fine, it’s just the grdimage that gmt doesn’t like in this perspective mode.

The DEM/grid file is fine by the way, I plot it in the same subfigure just before for a global map using “-JN”, so the problem is the “-JG” projection or something else.

Happy to provide more detail/code/variables/images/data if and when needed.

Many thanks for any help in advance!

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<div class="post-metadata">

**Author:** ![Joaquim](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/joaquim/32/16_2.png) [@Joaquim](https://forum.generic-mapping-tools.org/u/Joaquim)\
**Post date:** [April 1, 2024, 5:45pm UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759/2 "2024-04-01T17:45:54Z")

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We need a reproducible command (there is no -p in the command that you say it fails). And no $$${…} please. For example, I use Windows.

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<div class="post-metadata">

**Author:** ![gaiastucky](https://avatars.discourse-cdn.com/v4/letter/g/f475e1/32.png) [@gaiastucky](https://forum.generic-mapping-tools.org/u/gaiastucky)\
**Post date:** [April 1, 2024, 6:40pm UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759/3 "2024-04-01T18:40:17Z")

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Sure! Here is a reduced form of the script:

```auto
#!/bin/bash

# Set parameters for the most beautiful plot
gmt set PS_LINE_CAP = round
gmt set PS_LINE_JOIN = miter
gmt set FONT_LABEL 16p,Helvetica,Black
gmt set FONT_ANNOT_PRIMARY 12p,Helvetica,Black
gmt set FORMAT_GEO_OUT = D
gmt set FORMAT_GEO_MAP = D
gmt set PS_MEDIA = a2
gmt set FONT_TAG = auto,Helvetica-Bold
gmt set MAP_FRAME_TYPE plain
gmt set PS_PAGE_ORIENTATION = landscape
gmt set PROJ_ELLIPSOID = Mars

#plotting options:
latitude=-80; longitude=0; altitude=1000; tilt=45; azimuth=210; twist=60; Width=20; Height=20
mapheight=3i
gmt begin mars_test
    gmt subplot begin 1x2 -Fs5i,5i/5i -M0.2i -Ad+gwhite+v+jTL -Ba0
        gmt subplot set 
        PROJ1="-JN0/${mapheight}+dh"
        gmt basemap $PROJ1 -Bnswe+gslategray -Rg
        gmt grdimage $PROJ1 ./mars_dem.tif -C'matlab/copper' -t35 -I+a-45+nt0.5+m0

        gmt subplot set
        PROJ2=-JG${longitude}/${latitude}/12c+z${altitude}+a${azimuth}+t${tilt}+w${twist}+v${Width}/${Height}
        gmt basemap $PROJ2 -Rg -BESnw+gslategray -By10g5 -Ba20xg10
        #gmt grdimage $PROJ2 ./mars_dem.tif -C'matlab/copper' -t35 -I+a-45+nt0.5+m0 -BESnw #doesnt work

    gmt subplot end
gmt end show

```

I’ve uploaded the DEM as well!  
[mars\_dem.tif](https://forum.generic-mapping-tools.org/uploads/short-url/5GiW0RTNMSmNvb2OnTXkOHi2SEH.tif) (507.2 KB)

I can plot the first subfigure with JN, but the second one doesnt work with JG… I’ve tried grdview, but if I have to supply a -p I am not sure how the variables would be set to match?

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<div class="post-metadata">

**Author:** ![Joaquim](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/joaquim/32/16_2.png) [@Joaquim](https://forum.generic-mapping-tools.org/u/Joaquim)\
**Post date:** [April 1, 2024, 11:43pm UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759/4 "2024-04-01T23:43:24Z")

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No variables (`${...}`) and avoid bash scripts remember? One-liners are enough.

```auto
gmt grdimage mars_dem.tif -t35 -I+a-45+nt0.5+m0 -BESnw -JG0/-80/12c+z1000+a210+t45+w60+v20/20 -png lixo

```

GDAL is not able to recognize that projection. Convert the tif file to netcdf with `grdconvert` and it will work.

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<div class="post-metadata">

**Author:** ![gaiastucky](https://avatars.discourse-cdn.com/v4/letter/g/f475e1/32.png) [@gaiastucky](https://forum.generic-mapping-tools.org/u/gaiastucky)\
**Post date:** [April 2, 2024, 2:11am UTC](https://forum.generic-mapping-tools.org/t/how-to-plot-dem-grid-using-jg-perspective-projection/4759/5 "2024-04-02T02:11:48Z")

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Adding:

`gmt grdconvert ./grids/mars_dem.tif -G./grids/mars_dem.nc`

now makes it work! Muito obrigada!