Proj4 work with grdproject problem

Q&A
1

Hello:
when run this code:

gmt grdproject AP_14636_FBD_F6850_RT1.dem.grd -J"+proj=utm +zone=58 +south +datum=WGS84 +units=m +no_defs +to+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs" -C -F -Gtest123.grd

it will run forever and not return a result,why ?
I try to convert utm grid to wgs84 geodetic coordinates.
When I use this command:

gmt grdproject AP_14636_FBD_F6850_RT1.dem.grd -Ju-58/1:1 -C -Fe -I -GAP_14636_FBD_F6850_RT1.dem_Geodetic.grd

it can return a good look result,but also return an Error:
ERROR 1: PROJ: proj_create: Error -13: major axis or radius = 0 or not given

I browsed and it seemed to be caused by PROJ4,Thanks a lot!please help!

2

When I experiment with synthetic data I get this

gmt grdmath -R162/168/-10/0 -I0.1 X Y MUL = lixo.grd

gmt grdproject lixo.grd -J"+proj=utm +zone=58 +south +datum=WGS84 +units=m +no_defs" -Glixo_utm.grd

gmt grdproject lixo_utm.grd -I -J"+proj=utm +zone=58 +south +datum=WGS84 +units=m +no_defs" -Glixo_geo2.grd
First opt_R      164.000000000000/166.000000000000/-6.007148010123/-4.007148010123      1.71944e+09     3.71911e+08
Second opt_R     161.953987660797/-10.013533960436/168.046012339203/0.000000000000r
grdproject [WARNING]: Unknown conversion between GMT and GDAL ellipsoid names. Using a generic spherical body.

I find that warning worrisome and don’t get it why it’s complaining.

Your example also hangs for me (but it’s computing something).

3

Thanks for reply,I turned a another way,and it work well.

gdalwarp -t_srs EPSG:4326 -s_srs EPSG:32758 AP_15059_FBS_F6860_RT1.dem.tif AP_15059_FBS_F6860_RT1_Geodetic.dem.tif

As above,I use gdal directly,but I also want to konw why gmt return an error.

4

I will try to debug the source of that error message when I have time.

5

When I use gdalwarp,it can’t deal with the data in irreagular area.
The data in utm projection:

Snipaste_2020-04-20_21-28-08
Snipaste_2020-04-20_21-28-08705×687 112 KB

When I use gdalwarp(gdalwarp -t_srs EPSG:4326 -s_srs EPSG:32758 source.tif aim.tif)to get geodetic coordinates in WGS84:
Snipaste_2020-04-20_21-27-54
Snipaste_2020-04-20_21-27-54849×687 134 KB

Anyway,Thank you！Joaquim！

6

Strange that gdalwarp behavior. Note, your case is simple to do with the GMT syntax only. It should be something around (not sure how to set the suthern hemisphere (-Ju58S/1:1 ?)

gmt grdproject -I -C -F -R162/168/-10/0 -Ju-58/1:1 ...
7

@Mark I fixed the ellipsoid names issue (it was a silly bug while comparing text strings), but the other one is tougher. Possibly related to this https://github.com/GenericMappingTools/gmt/issues/3147

8

Thanks a lot，Joaquim！

9

and another question:Why after grdblend ,the grid spacing changed?
Hope help! Big Thanks!