What is the quickest way to do a coordinate transformation in gmt 6

Q&A
1

Hello! I often deal with point coordinates and wish I had a calculator that would quickly take me from EPSG:4230 to EPSG:4258 in 5 seconds. Is there a way to achieve such conversion from the terminal in one line? I’m reading the documentation on mapproject but there aren’t any conversion examples. Grass GIS has m.proj [coordinate] [proj_in] [proj_out] I’m sure GMT has something equivalent? Thanks in advance!

2

What units are your data in?

I think that you might be interested in the mapproject -T option? I tried to work out how to do it, but got stuck working out how to specify the datums. One thing to note is the EPSG:4258 uses the GRS-80 ellipsoid, whereas EPSG:4230 uses WGS-84. PROJ_ELLIPSOID (set using gmtset) is your friend here - I think.

3

I would just make a function which takes input coordinates (and optionally EPSG to/from) and use gdaltransform.

E.g.

echo 34.5 76.5 | gdaltransform -s_srs EPSG:4230 -t_srs EPSG:4258
5

Hi Tim - EPSG:4230 is essentially the old european datum (ED50). It used the Intl24 ellipsoid, which is basically Hayford 1909, it predates both GRS80 and WGS84. I often have coordinates from old reports that use that datum and it would be cool to just convert on the fly (from the terminal) rather than load into a GIS software. Coordinates can be in Decimal Degrees, DMS it could be anything.

6

Hi Andreas, unfortunately that returns nothing, not even an error. I tried prephasing with gmt and then says “no module named gdaltransform was found”. I’m running gmt 6 if that helps

7

On Windows you have a gdaltransform.exe but on *nix you need GDAL utilities installed as well. Anyway, no need here

echo 34.5 76.5 | gdaltransform -s_srs EPSG:4230 -t_srs EPSG:4258
34.4990350686626 76.5004446574769 0

echo 34.5 76.5 | mapproject -JEPSG:4230+toEPSG:4258
34.4990350687   76.5004446575
8

Hi Joaquim and thanks for the reply! Second method (mapproject) works fine, I’ll be using that! You’ve resolved my question, but curious why the first method, gdaltransform doesn’t return anything. I am currently running gmt6 on windows using GIT with Bash. Is gdaltransform.exe part of the regular install or is it additional?

9

What GMT version?

In GMT6.1.1 and GMT6.1.0 (I think), all GDAL executables are shipped in the installer, so you should have a gdaltranslate.exe in your GMT6/bin directory.

10

GMT 6.1.1 and I confirm that gdaltranslate.exe is in my GMT6 bin. Bizzare!

myname@LAPTOP-2HIQP1UT MINGW64 /c
$ echo 34.5 76.5 | gdaltransform -s_srs EPSG:4230 -t_srs EPSG:4258

myname@LAPTOP-2HIQP1UT MINGW64 /c
$ echo 3 50 | mapproject -JEPSG:4258+toEPSG:4230
3.00128973945 50.0008728489

11

Same if you run the gdaltrasform from a pure cmd window?

12

Wow, works from cmd, no issues

13

Sorry @RunningWild, gdaltransform is part of gdal, not GMT.

Anyway, if you do this command often, consider putting something like

coordtrans() {
echo ${1} ${2} | mapproject -JEPSG:4230+toEPSG:4258
}

in your .bashrc (or whatever git with bash is using). Then you simply have to do:

$ coordtrans 34.5 76.5
34.4987921573	76.5004822999
14

Strange. It works for me with the GIT bash too.