# Grdcut warping and distorting output raster **URL:** \ **Category:** Q&A\ **Tags:** gmt\ **Created:** [April 1, 2021, 9:04pm UTC](https://forum.generic-mapping-tools.org/t/grdcut-warping-and-distorting-output-raster/1523 "2021-04-01T21:04:26Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![jpschmidt](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/jpschmidt/32/700_2.png) [@jpschmidt](https://forum.generic-mapping-tools.org/u/jpschmidt)\ **Post date:** [April 1, 2021, 9:04pm UTC](https://forum.generic-mapping-tools.org/t/grdcut-warping-and-distorting-output-raster/1523/1 "2021-04-01T21:04:26Z")
I am having an issue that has recently occurred with newer versions of GMT. I had a netCDF raster image of central NM that I was cutting with grdcut in using the following lines ``` >> LATMIN=33.8000462963 >> LATMAX=34.6204166667 >> LONMIN=-107.251898148 >> LONMAX=-106.497453704 >> gmt grdcut smb_elevation.nc -R$LONMIN/$LONMAX/$LATMIN/$LATMAX -Gsmb_topo.nc -V ``` As I mentioned, this was line of code was working just fine prior to upgrading GMT. I’ll also note that I have had to upgrade my macbook to Big Sur recently so a lot of upgrades have occurred recently. This line specifically seems to later my output \*.nc file so that it looks completely warped. Here is the verbose output from executing that line. > grdcut [INFORMATION]: Processing input grid > grdcut [INFORMATION]: File smb\_elevation.nc reads with GDAL driver HFA > grdcut [INFORMATION]: Cartesian input grid > grdcut [INFORMATION]: Round-off patrol changed grid limit for xmin from -108.0005092597349 to -108.0005092597349 > grdcut [INFORMATION]: Round-off patrol changed grid limit for xmax from -105.9994907412076 to -105.9994907412076 > grdcut [INFORMATION]: Round-off patrol changed grid limit for ymin from 32.99949074088585 to 32.99949074088585 > grdcut [INFORMATION]: Round-off patrol changed grid limit for ymax from 35.00050925941316 to 35.00050925941316 > grdcut [INFORMATION]: Reading grid from file smb\_elevation.nc > grdcut [INFORMATION]: Read band(s): 1 > grdcut [INFORMATION]: Set boundary condition for all edges: natural > grdcut [INFORMATION]: Set boundary condition for left edge: natural > grdcut [INFORMATION]: Set boundary condition for right edge: natural > grdcut [INFORMATION]: Set boundary condition for bottom edge: natural > grdcut [INFORMATION]: Set boundary condition for top edge: natural > grdcut [INFORMATION]: File spec: W E S N dx dy n\_columns n\_rows: > grdcut [INFORMATION]: Old:grdcut [INFORMATION]: -108.00050926 -105.999490741 32.9994907409 35.0005092594 9.2592592538e-05 9.25925925959e-05 21612 21612 > grdcut [INFORMATION]: New:grdcut [INFORMATION]: -107.251898148 -106.497453704 33.8000462963 34.6204166667 9.2592592538e-05 9.25925925959e-05 8149 8861 > grdcut [INFORMATION]: Writing grid to file smb\_topo.nc > grdcut [INFORMATION]: Proj4 string to be converted to WKT: > +proj=longlat +datum=NAD83 +no\_defs > grdcut [INFORMATION]: WKT converted from proj4 string: > GEOGCS[“unknown”, > DATUM[“North\_American\_Datum\_1983”, > SPHEROID[“GRS 1980”,6378137,298.257222101, > AUTHORITY[“EPSG”,“7019”]], > AUTHORITY[“EPSG”,“6269”]], > PRIMEM[“Greenwich”,0, > AUTHORITY[“EPSG”,“8901”]], > UNIT[“degree”,0.0174532925199433, > AUTHORITY[“EPSG”,“9122”]], > AXIS[“Longitude”,EAST], > AXIS[“Latitude”,NORTH]] I can follow most of the output till the line about Proj4 string to be converted to WKT. I’ll also give the output from grdinfo. > smb\_elevation.nc: Title: Grid imported via GDAL > smb\_elevation.nc: Command: > smb\_elevation.nc: Remark: > smb\_elevation.nc: Gridline node registration used [Geographic grid] > smb\_elevation.nc: Grid file format: gd = Import/export through GDAL > smb\_elevation.nc: x\_min: -108.00050926 x\_max: -105.999490741 x\_inc: 9.2592592593e-05 name: x n\_columns: 21612 > smb\_elevation.nc: y\_min: 32.9994907409 y\_max: 35.0005092594 y\_inc: 9.2592592593e-05 name: y n\_rows: 21612 > smb\_elevation.nc: z\_min: 1259.08984375 z\_max: 2504.15893555 name: z > smb\_elevation.nc: scale\_factor: 1 add\_offset: 0 > +proj=longlat +datum=NAD83 +no\_defs Attached is an image from QGIS where I could look at both rasters and you can see how the output raster gets warped after the grdcut conversion. the original “smb\_elevation.nc” was created in QGIS from image rasters downloaded from the USGS national map as IMG formatted files. For easy use in GMT, I did the conversion here. I’m not sure if projection/header information is incorrect, but this function (grdcut) was working on this file before I had to upgrade my GMT package. Any help or advice on how to work this would be appreciated. ![Screen Shot 2021-04-01 at 4.59.48 PM](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/6/66ab1bb60a7ca0013870ea1e1930a59ac1faadc7.jpeg) ---
**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:** [April 3, 2021, 6:48pm UTC](https://forum.generic-mapping-tools.org/t/grdcut-warping-and-distorting-output-raster/1523/2 "2021-04-03T18:48:40Z")
Hard to examine without being able to recreate - and I know your input grid is very big. Maybe @Joaquim has some thoughts on how to sort this out? ---
**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:** [April 3, 2021, 11:14pm UTC](https://forum.generic-mapping-tools.org/t/grdcut-warping-and-distorting-output-raster/1523/3 "2021-04-03T23:14:53Z")
Have no idea. I guess that _raster images_ are actually grids, right? What happen when you do a `grdimage` plot of the grdcut’ed grid? Does it screws for all sizes of the sub-region or only big ones?