# Grdinterpolate -E output units in m? **URL:** \ **Category:** Q&A\ **Created:** [June 21, 2023, 11:58am UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056 "2023-06-21T11:58:47Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![bru](https://avatars.discourse-cdn.com/v4/letter/b/90db22/32.png) [@bru](https://forum.generic-mapping-tools.org/u/bru)\ **Post date:** [June 21, 2023, 11:58am UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/1 "2023-06-21T11:58:47Z")
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? ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [June 21, 2023, 12:17pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/2 "2023-06-21T12:17:27Z")
No documentation taht says +i100k will be processed as km so it remains meter. Use grdedit to switch by 100 if you prefer that. ---
**Author:** ![bru](https://avatars.discourse-cdn.com/v4/letter/b/90db22/32.png) [@bru](https://forum.generic-mapping-tools.org/u/bru)\ **Post date:** [June 21, 2023, 2:18pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/3 "2023-06-21T14:18:59Z")
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. ---
**Author:** ![bru](https://avatars.discourse-cdn.com/v4/letter/b/90db22/32.png) [@bru](https://forum.generic-mapping-tools.org/u/bru)\ **Post date:** [June 21, 2023, 3:52pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/4 "2023-06-21T15:52:22Z")
?var actually only recognizes the named variables in z… if anyone has any clue please help, I’ve tried everything!! ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [June 21, 2023, 4:00pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/5 "2023-06-21T16:00:57Z")
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. ---
**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:** [June 21, 2023, 4:30pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/6 "2023-06-21T16:30:20Z")
`grdedit -R...` should be the way to go. ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [June 22, 2023, 11:12am UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/7 "2023-06-22T11:12:31Z")
> [@bru](#): > > If no units are specified we default to great circle distances in km (if geographic). You are right about that. Shall see what we are doing with units here. ---
**Author:** ![bru](https://avatars.discourse-cdn.com/v4/letter/b/90db22/32.png) [@bru](https://forum.generic-mapping-tools.org/u/bru)\ **Post date:** [June 22, 2023, 12:51pm UTC](https://forum.generic-mapping-tools.org/t/grdinterpolate-e-output-units-in-m/4056/8 "2023-06-22T12:51:16Z")
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 ```