# Projection errors **URL:** \ **Category:** PyGMT Q&A\ **Created:** [November 22, 2021, 9:02pm UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342 "2021-11-22T21:02:54Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Sistjerne](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/sistjerne/32/3772_2.png) [@Sistjerne](https://forum.generic-mapping-tools.org/u/Sistjerne)\ **Post date:** [November 22, 2021, 9:02pm UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/1 "2021-11-22T21:02:54Z")
Hi PyGMT experts, Thank you for making PyGMT, and for the great efforts in updating and improving the packages. It is very much appreciated. I have two issues. Do I need to make two different topics? I am using ``` pygmt. __version__'v0.5.1.dev15' ``` ## The first issue: This may be a bug. I a trying to make a polar sterographic plot of Antarctica, but it is only working when I use projection -Js and not -JS (using ordinary GMT notation). Here, is an example: ``` grid = pygmt.datasets.load_earth_relief(resolution="05m", region=[-180,180,-90,-40]) fig = pygmt.Figure() fig.basemap(region="-130/-50/45/-50r", projection="S0/-90/-70/8c", frame="a20f20") ``` I get this error: ``` basemap [ERROR]: Option -J parsing failure. Correct syntax: -Js/[/]/ OR -JS/[/]/ is distance from center to perimeter (< 180, default 90) is <1:xxxx>, /<1:xxxx>, or (in cm)/, or use in cm basemap [ERROR]: Offending option -JS0/-90/-70/8c Traceback (most recent call last): File "", line 1, in File "/g5/procdata/skr/anaconda3/envs/pygmt4/lib/python3.9/site-packages/pygmt/helpers/decorators.py", line 586, in new_module return module_func(*args, **kwargs) File "/g5/procdata/skr/anaconda3/envs/pygmt4/lib/python3.9/site-packages/pygmt/helpers/decorators.py", line 726, in new_module return module_func(*args, **kwargs) File "/g5/procdata/skr/anaconda3/envs/pygmt4/lib/python3.9/site-packages/pygmt/src/basemap.py", line 84, in basemap lib.call_module("basemap", build_arg_string(kwargs)) File "/g5/procdata/skr/anaconda3/envs/pygmt4/lib/python3.9/site-packages/pygmt/clib/session.py", line 500, in call_module raise GMTCLibError( pygmt.exceptions.GMTCLibError: Module 'basemap' failed with status code 72: basemap [ERROR]: Option -J parsing failure. Correct syntax: basemap [ERROR]: Offending option -JS0/-90/-70/8c ``` This works with no problems: ``` grid = pygmt.datasets.load_earth_relief(resolution="05m", region=[-180,180,-90,-40]) fig = pygmt.Figure() fig.basemap(region="-130/-50/45/-50r", projection="s0/-90/-70/1:5000000", frame="a20f20") fig.grdimage(grid=grid, cmap="gray") fig.savefig('test.png', show=True) ``` Am I doing something wrong? I have tried to plot the same thing with a northern polar stereographic projection (projection="S-45/90/70/8c), but with no issues. I can live with using the “Js” solution, but I just find it strange, ## Second issue I would like to plot projected data on top of an earth relief grid. How do I do this? Do I need to reproject the earth relief data first? I have used this example [(42) Antarctica and stereographic data — GMT 6.6.0 documentation](https://docs.generic-mapping-tools.org/latest/gallery/ex42.html) to plot fx. coastlines in geographical coordinates on top of my projected data. This works, but when I start by using the geographical coordinates (fx. plotting earth relief as a background) with my projected data on top it goes wrong: ``` # grid_relief = pygmt.datasets.load_earth_relief(resolution="05m", region=[-180, 180, -90, -40) region = "-130/-52/45/-50r" fig = pygmt.Figure() # fig.grdimage(grid=grid_relief, region=regionr, cmap="gray", projection="s0/-90/-70/1:50000000") ## Wanted to make a background map pygmt.config(PROJ_ELLIPSOID="WGS-84") pygmt.makecpt(cmap="devon", series=[0,100]) fig.grdimage(grid=ds, cmap=True, projection="x1:50000000") ## My projected data (test.nc) fig.basemap(region=region, projection="s0/-90/-70/1:50000000", frame=[frame[0], frame[1], f'+t"{title}"']) fig.coast(shorelines="0.5p,black", projection=""s0/-90/-70/1:50000000, frame=['WSEn', frame[0], frame[1]]) ``` I have uncommented the lines that do not work! My workaround right now is to reproject my input data through Pythons pyproj, but I guess it is possible in pyGMT to plot it without the reprojection.! Below I have attached two figures. The first shows my projected data (satellite tracks) without the background relief and the second figure show the background image, but no projected data. ![working_no_relief](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/e/e1cfdd7ca267ddfb1c12d1a94a7ca91d733545dd.png) ![not_working_relief](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/e/e20b03ec2b2f06657a264638ec54ee34a19b268d.png) I have also played around with grdproject, but this does not give me any valied values: ``` ds_proj = pygmt.grdproject(grid=ds, projection="s0/-90/-70/1:50000000", region=regionr, inverse=True) ``` ---
**Author:** ![Esteban82](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/esteban82/32/54_2.png) [@Esteban82](https://forum.generic-mapping-tools.org/u/Esteban82)\ **Post date:** [November 22, 2021, 9:11pm UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/2 "2021-11-22T21:11:52Z")
About the first issue, I think that the horizon parameter of -JS should be a positive number even if you are working on the south pole. Maybe you could try using: ```auto projection="S0/-90/70/8c", ``` ---
**Author:** ![weiji14](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/weiji14/32/33_2.png) [@weiji14](https://forum.generic-mapping-tools.org/u/weiji14)\ **Post date:** [November 22, 2021, 10:23pm UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/3 "2021-11-22T22:23:37Z")
Hi @Sistjerne! Yeah, as @Esteban82 mentioned, the `projection` information might need to be a positive number for some reason, I felt like this was a bug introduced sometime around GMT 6.1 or 6.2… As for your 2nd problem, instead of the earth\_relief grid (SRTM based), I recommend using the Reference Elevation Model of Antarctica (REMA) since it is already in the Antarctic Stereographic Projection (EPSG:3031), so no need to reproject (plus the earth\_relief grid uses REMA as the source anyway). You can then overlay your projected data on top easily. Get it at: - [Index of /elev/dem/setsm/REMA/mosaic/v1.1/1km](https://data.pgc.umn.edu/elev/dem/setsm/REMA/mosaic/v1.1/1km/) - [Index of /elev/dem/setsm/REMA/mosaic/v1.1/200m](https://data.pgc.umn.edu/elev/dem/setsm/REMA/mosaic/v1.1/200m/) E.g. use `pygmt.which("https://data.pgc.umn.edu/elev/dem/setsm/REMA/mosaic/v1.1/200m/REMA_200m_dem_filled.tif", download=True)` to download the GeoTIFF file. Tip: If you want to plot the Antarctic grounding line, you could try: ```python fig.coast( region="REMA_200m_dem_filled.tif", # or specify in EPSG:3031 coordinates [minx, maxx, miny, maxy] projection="s0/-90/-71/1:30000000", area_thresh="+ag", resolution="i", shorelines="0.25p", # frame="ag", ) ``` P.S. I have some code from a poster this year at [https://nbviewer.org/github/weiji14/nzasc2021/blob/main/key\_figure.ipynb#Figure-of-Antarctic-active-subglacial-lake-map](https://nbviewer.org/github/weiji14/nzasc2021/blob/main/key_figure.ipynb#Figure-of-Antarctic-active-subglacial-lake-map) and [nzasc2021/key\_figure.py at 15851c3ea797ae2cccf7b10f3d08f498a5314d3e · weiji14/nzasc2021 · GitHub](https://github.com/weiji14/nzasc2021/blob/15851c3ea797ae2cccf7b10f3d08f498a5314d3e/key_figure.py#L367-L416) that might be helpful ![image](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/5/5b93f01733c82ae9060e687c81d8eb0c1b48a697.jpeg) P.P.S. I have some older code (using PyGMTv0.1/GMT 6.0) that may be helpful at [deepbedmap/paper\_figures.py at 0e766fb5789700e63ac38029bd5a0499838431a5 · weiji14/deepbedmap · GitHub](https://github.com/weiji14/deepbedmap/blob/0e766fb5789700e63ac38029bd5a0499838431a5/paper_figures.py#L521-L584) and [https://nbviewer.org/github/weiji14/deepbedmap/blob/v1.1.0/paper\_figures.ipynb](https://nbviewer.org/github/weiji14/deepbedmap/blob/v1.1.0/paper_figures.ipynb). ---
**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:** [November 23, 2021, 12:05am UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/4 "2021-11-23T00:05:33Z")
> [@Sistjerne](#): > > `S0/-90/-70/8c` There is no option to select map _width_ ( **-JS** ) **and** also specify a specific _latitude_ and _radius_ (-70/8c). That can only be done when you specify a _scale_ ( **-Js** ). ---
**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:** [November 23, 2021, 3:31am UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/5 "2021-11-23T03:31:38Z")
I have added a bit more checking in master which would give an error for your failing command. I also improved parsing a bit and updated the docs to be clearer on a few items related to -Js|S. ---
**Author:** ![Sistjerne](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/sistjerne/32/3772_2.png) [@Sistjerne](https://forum.generic-mapping-tools.org/u/Sistjerne)\ **Post date:** [November 23, 2021, 9:32am UTC](https://forum.generic-mapping-tools.org/t/projection-errors/2342/6 "2021-11-23T09:32:28Z")
Thank you very much for the thorough answers. I have fixed all my issues! I can use the projection: ``` projection="S0/-90/70/8c" ``` @weiji14 I really appreciate all your examples. I have indeed learned a lot new about pyGMT by looking at them!