Grdinterpolate -E output units in m?

Q&A
1

Hi all!

I’m using grdinterpolate to find values over a vertical cross section, however it seems like the X axis output units are being given in m? Is there a way to set it to be given in km?

The command line I’m using:

gmt grdinterpolate $ingrid -G$outgrid -E-80/-15/-5/-15+i100k" -T0/800/1

which gives me: x_min: 0 x_max: 8012484.78674 x_inc: 100.034767678

however, I know I’m measuring a range of 75 degrees ~ 8330 km, so it seems the output is in meters? Or am I doing something wrong?

I highly appreciate any help!

Thanks, Bruna.

*should I attach the input 3D grid?

2

No documentation taht says +i100k will be processed as km so it remains meter. Use grdedit to switch by 100 if you prefer that.

3

Thank you! I guess I got confused with the part:
If no units are specified we default to great circle distances in km (if geographic).
from the documentation and was trying to find a way to get to it.

Your solution unfortunately is leading me to another error. My GMT is not allowing me to call variables from netCDF files. If I use $mygrid?var for anything it gives me “Named variable does not exist in file”.

Ex: the grid I’m working on, from grdinfo
x_min: 0 x_max: 8012484.78674 x_inc: 111284.510927 name: longitude n_columns: 73

and if I try
gmt grdedit$mygrid?longitude it gives
grdinfo (gmtapi_import_grid): Named variable does not exist in file [v.-80.-15.-5.-15.grd?longitude]
[Session gmt (0)]: Error returned from GMT API: GMT_GRID_READ_ERROR (18)
[Session gmt (0)]: Error returned from GMT API: GMT_GRID_READ_ERROR (18)

I tested with other netCDF grids and still get the same error…

Thanks for the support!

Bruna.

4

?var actually only recognizes the named variables in z…

if anyone has any clue please help, I’ve tried everything!!

5

Yes. GMT has never let anyone access a coordinate array since most of the time there is none, just the scalars min, inc, max. Only grids or cube layers can be accessed.

6

grdedit -R... should be the way to go.

1 Like
7

You are right about that. Shall see what we are doing with units here.

1 Like
8

Perfect, this does the trick for now! Thanks a lot!!

For anyone with a similar problem, here is how I’m getting around:

#run your interpolate options for a cross-section
gmt grdinterpolate $ingrid -G$outgrid -E$lon1/$lat1/$lon2/$lat2 -T$zmin/$zmax/$zinc -fg
#calculate the max crossing distance and convert to kilometers
dmax=$(gmt grdinfo -C -Q $outgrid | awk '{print $3/1000}')
#reset the values in kilometers
gmt grdedit -R0/$dmax/$zmin/$zmax $ingrid