UTM to lat/lon .grd file

Hi, all.
I am new to GMT and am having trouble with the mapproject and grdproject commands to transform UTM to Lat/Lon in a grid file. I believe I am entering everything correctly but I’ve only been using GMT for about 2 weeks so I’m still learning. I have a UTM grid file in zone 27N and here is how I have tried entering the command:

gmt grdproject eyjafjardarall_s_utm27_10mEIK.grd -Ju+27 -I

gmt mapproject eyjafjardarall_s_utm27_10mEIK.grd -Ju+27 -C -I -F

Each time it generates a file but the file is not the correct lat/lon :frowning: Does anyone have some guidance for me on what I’m doing wrong/how I should be going about it? Thank you!

mapproject is for vector data. It could never work with grids. Try

gmt grdproject eyjafjardarall_s_utm27_10mEIK.grd -Ju+27/1:1 -I -C -F