strange error when attempting to generate a map using 'geos' projection

_Dr_Phillip_M_Feldma · January 24, 2010, 6:59am

I’ve been experimenting with basemap, and have been able to make maps using
the orthographic and polyconic projections. When I try to generate a map
using the geostationary projection, I get the error message shown below. I
haven’t been able to make head or tail of this message; any advice will be
appreciated.

Phillip

RuntimeError Traceback (most recent call last)

C:\Phillip\pmap.py in <module>()
   6163
   6164 # Create basemap object:
-> 6165 map= Basemap(**map_parms)
   6166 ax= fig.add_axes([0.1,0.08,0.7,0.82])
   6167

C:\Python25\lib\site-packages\mpl_toolkits\basemap\__init__.pyc in
__init__(self, llcrnrlon, llc
rnrlat, urcrnrlon, urcrnrlat, llcrnrx, llcrnry, urcrnrx, urcrnry, width,
height, projection, res
olution, area_thresh, rsphere, lat_ts, lat_1, lat_2, lat_0, lon_0, lon_1,
lon_2, no_rot, suppres
s_ticks, satellite_height, boundinglat, fix_aspect, anchor, ax)
    680
    681 # initialize proj4
--> 682 proj =
Proj(projparams,self.llcrnrlon,self.llcrnrlat,self.urcrnrlon,self.urcrnrl
at)
    683
    684 # make sure axis ticks are suppressed.

C:\Python25\lib\site-packages\mpl_toolkits\basemap\proj.pyc in
__init__(self, projparams, llcrnr
lon, llcrnrlat, urcrnrlon, urcrnrlat, urcrnrislatlon)
    117 urcrnry = -llcrnry
    118 elif self.projection == 'geos':
--> 119 self._proj4 = pyproj.Proj(projparams)
    120 # find major and minor axes of ellipse defining map proj
region.
    121 # h is measured from surface of earth at equator.

C:\Python25\lib\site-packages\mpl_toolkits\basemap\pyproj.pyc in
__new__(self, projparams, **kwa
rgs)
    146 kvpairs.append(kvpair+' ')
    147 projstring = ''.join(kvpairs)
--> 148 return _Proj.__new__(self, projstring)
    149
    150 def __call__(self, *args, **kw):

C:\Python25\lib\site-packages\mpl_toolkits\basemap\_proj.pyd in
_proj.Proj.__cinit__ (src/_proj.
c:587)()
     23
     24
---> 25
     26
     27

RuntimeError: unknown prime meridian conversion id
WARNING: Failure executing file: <pmap.py>

···

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_Jeff_Whitaker1 · January 24, 2010, 2:05pm

Dr. Phillip M. Feldman wrote:

I’ve been experimenting with basemap, and have been able to make maps using
the orthographic and polyconic projections. When I try to generate a map
using the geostationary projection, I get the error message shown below. I
haven’t been able to make head or tail of this message; any advice will be
appreciated.

Phillip

RuntimeError Traceback (most recent call last)

C:\Phillip\pmap.py in <module>()
   6163
   6164 # Create basemap object:
-> 6165 map= Basemap(**map_parms)
   6166 ax= fig.add_axes([0.1,0.08,0.7,0.82])
   6167

C:\Python25\lib\site-packages\mpl_toolkits\basemap\__init__.pyc in
__init__(self, llcrnrlon, llc
rnrlat, urcrnrlon, urcrnrlat, llcrnrx, llcrnry, urcrnrx, urcrnry, width,
height, projection, res
olution, area_thresh, rsphere, lat_ts, lat_1, lat_2, lat_0, lon_0, lon_1,
lon_2, no_rot, suppres
s_ticks, satellite_height, boundinglat, fix_aspect, anchor, ax)
    680
    681 # initialize proj4
--> 682 proj =
Proj(projparams,self.llcrnrlon,self.llcrnrlat,self.urcrnrlon,self.urcrnrl
at)
    683
    684 # make sure axis ticks are suppressed.

C:\Python25\lib\site-packages\mpl_toolkits\basemap\proj.pyc in
__init__(self, projparams, llcrnr
lon, llcrnrlat, urcrnrlon, urcrnrlat, urcrnrislatlon)
    117 urcrnry = -llcrnry
    118 elif self.projection == 'geos':
--> 119 self._proj4 = pyproj.Proj(projparams)
    120 # find major and minor axes of ellipse defining map proj
region.
    121 # h is measured from surface of earth at equator.

C:\Python25\lib\site-packages\mpl_toolkits\basemap\pyproj.pyc in
__new__(self, projparams, **kwa
rgs)
    146 kvpairs.append(kvpair+' ')
    147 projstring = ''.join(kvpairs)
--> 148 return _Proj.__new__(self, projstring)
    149
    150 def __call__(self, *args, **kw):

C:\Python25\lib\site-packages\mpl_toolkits\basemap\_proj.pyd in
_proj.Proj.__cinit__ (src/_proj.
c:587)()
     23
     24
---> 25
     26
     27

RuntimeError: unknown prime meridian conversion id
WARNING: Failure executing file: <pmap.py>

Philip: That's an error from the proj4 c library saying that it didn't like one of the parameters you used to define the projection. Since you didn't include the parameters you used, I can't say which one is the culprit.

-Jeff

_Dr_Phillip_M_Feldma · January 24, 2010, 6:25pm

Jeff Whitaker wrote:

<snip>
Philip: That's an error from the proj4 c library saying that it didn't
like one of the parameters you used to define the projection. Since you
didn't include the parameters you used, I can't say which one is the
culprit.

-Jeff

I've boiled the code down to something small that demonstrates the problem.
Thanks!
http://old.nabble.com/file/p27297693/temp.py temp.py

···

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_Jeff_Whitaker1 · January 25, 2010, 3:03am

Dr. Phillip M. Feldman wrote:

Jeff Whitaker wrote:

<snip>
Philip: That's an error from the proj4 c library saying that it didn't like one of the parameters you used to define the projection. Since you didn't include the parameters you used, I can't say which one is the culprit.

-Jeff

Philip: I believe that lat_0 must be zero for the geostationary projection (you have to be looking down on the equator). I usually leave the lat_0 parameter off entirely, in which case zero is assumed. I'll try to catch that and raise a more insightful error message.

-Jeff

_Dr_Phillip_M_Feldma · January 25, 2010, 3:17am

Jeff Whitaker wrote:

Dr. Phillip M. Feldman wrote:

Jeff Whitaker wrote:

<snip>
Philip: That's an error from the proj4 c library saying that it didn't like one of the parameters you used to define the projection. Since you didn't include the parameters you used, I can't say which one is the culprit.

-Jeff

Philip: I believe that lat_0 must be zero for the geostationary projection (you have to be looking down on the equator). I usually leave the lat_0 parameter off entirely, in which case zero is assumed. I'll try to catch that and raise a more insightful error message.

-Jeff

Hm. I suppose that you are right. "Geostationary" does imply that the viewer is 35786.2 km above the equator.

What would be more useful is a geosynchronous projection. This would allow the viewer to be located at any latitude. Geostationary is a special case of geosynchronous.

Even more useful than a geosynchronous projection is a camera projection that allows one to place the viewer at any location in space (i.e., any latitude and longitude for the nadir point, and any altitude). (I wrote something like this is Fortran 25 years ago). Generalizing the existing geostationary projection to turn it into a camera projection would make it far more useful. I hope that someone will consider making this change.

Phillip