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Cannot plot a simple map over Africa if lon_0 is not equal to zero #347

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cpaulik opened this issue Mar 28, 2017 · 4 comments
Open

Cannot plot a simple map over Africa if lon_0 is not equal to zero #347

cpaulik opened this issue Mar 28, 2017 · 4 comments

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@cpaulik
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cpaulik commented Mar 28, 2017

This might be related to #183
I have a quite simple global 0.1 degree image that I would like to put onto a map. The code for reproducing the problem is the following.

    m = Basemap(width=12000000, height=8000000,
                resolution='l', projection='stere',
                lat_ts=0, lat_0=0, lon_0=21.)
    # m = Basemap(width=9000000, height=9000000,
    #             projection='aeqd', lat_0=0, lon_0=1)
    lons = np.arange(-179.95, 180.01, 0.1)
    lats = np.arange(-89.95, 90.01, 0.1)
    data = np.random.random((1800, 3600))
    lons, lats = np.meshgrid(lons, lats)
    x, y = m(lons, lats)
    m.pcolormesh(x, y, data,
                 latlon=False, cmap='RdBu')
    # m.imshow(np.flipud(anom)[1500:2470,600:1200])
    m.drawcoastlines()
    m.drawcountries()
    plt.show()

The result is the following:
basemap-stere_lon_0 21

Changing lon_0 from 21 to 0 gives the following:
basemap-stere_lon_0 0

I've also tried this with aeqd and laea projections with the same results.

conda environment for testing
name: test_basemap
channels:
- !!python/unicode
  'defaults'
- !!python/unicode
  'conda-forge'
dependencies:
- !!python/unicode
  'basemap=1.0.7=np112py27_0'
- !!python/unicode
  'cairo=1.14.8=0'
- !!python/unicode
  'cycler=0.10.0=py27_0'
- !!python/unicode
  'dbus=1.10.10=0'
- !!python/unicode
  'expat=2.1.0=0'
- !!python/unicode
  'fontconfig=2.12.1=3'
- !!python/unicode
  'freetype=2.5.5=2'
- !!python/unicode
  'functools32=3.2.3.2=py27_0'
- !!python/unicode
  'geos=3.5.0=0'
- !!python/unicode
  'glib=2.50.2=1'
- !!python/unicode
  'gst-plugins-base=1.8.0=0'
- !!python/unicode
  'gstreamer=1.8.0=0'
- !!python/unicode
  'icu=54.1=0'
- !!python/unicode
  'jpeg=9b=0'
- !!python/unicode
  'libffi=3.2.1=1'
- !!python/unicode
  'libgcc=5.2.0=0'
- !!python/unicode
  'libiconv=1.14=0'
- !!python/unicode
  'libpng=1.6.27=0'
- !!python/unicode
  'libxcb=1.12=1'
- !!python/unicode
  'libxml2=2.9.4=0'
- !!python/unicode
  'matplotlib=2.0.0=np112py27_0'
- !!python/unicode
  'mkl=2017.0.1=0'
- !!python/unicode
  'numpy=1.12.1=py27_0'
- !!python/unicode
  'openssl=1.0.2k=1'
- !!python/unicode
  'pcre=8.39=1'
- !!python/unicode
  'pip=9.0.1=py27_1'
- !!python/unicode
  'pixman=0.34.0=0'
- !!python/unicode
  'pycairo=1.10.0=py27_0'
- !!python/unicode
  'pyparsing=2.1.4=py27_0'
- !!python/unicode
  'pyqt=5.6.0=py27_2'
- !!python/unicode
  'python=2.7.13=0'
- !!python/unicode
  'python-dateutil=2.6.0=py27_0'
- !!python/unicode
  'pytz=2016.10=py27_0'
- !!python/unicode
  'qt=5.6.2=3'
- !!python/unicode
  'readline=6.2=2'
- !!python/unicode
  'setuptools=27.2.0=py27_0'
- !!python/unicode
  'sip=4.18=py27_0'
- !!python/unicode
  'six=1.10.0=py27_0'
- !!python/unicode
  'sqlite=3.13.0=0'
- !!python/unicode
  'subprocess32=3.2.7=py27_0'
- !!python/unicode
  'tk=8.5.18=0'
- !!python/unicode
  'wheel=0.29.0=py27_0'
- !!python/unicode
  'zlib=1.2.8=3'
prefix: !!python/unicode '/home/cpa/.pyenv/versions/miniconda-3.16.0/envs/test_basemap'
@WeatherGod
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WeatherGod commented Mar 28, 2017 via email

@guziy
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guziy commented Mar 28, 2017

Yes, I get this as well, I'll try look into this...

@guziy
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guziy commented Mar 29, 2017

Hi:

I do not think this is a shiftgrid issue. I think it is the problem with using projection coordinates at the boundaries that leads to having close points in the index space very far in the projection space, and the interpolation (happening in matplotlib) is plotting the values over some parts of the central region. I'll have to investigate it further and think of a good way to try to avoid this.

I do not have a solution yet, but here is a workaround (i.e. mask data outside the basemap view limits):

https://github.com/guziy/PyNotebooks/blob/master/basemap_issue347.ipynb

Cheers

@cpaulik
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cpaulik commented Mar 29, 2017

Thanks, The workaround is something I can easily use for now.

@guziy guziy mentioned this issue Apr 24, 2017
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@avipersin avipersin mentioned this issue Jun 5, 2018
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3 participants
@WeatherGod @cpaulik @guziy