Hi, the Basemap allskymap example (examples/allskymap.py in current git and basemap rev 1.0.2) plots buggy tissots if they cross the zero meridian and/or the poles (see http://web.physik.rwth- aachen.de/~winchen/unfixed_polarRegions_llskymap.png ).
The attached patch fixes this issue (see http://web.physik.rwth- aachen.de/~winchen/fixed_polarRegions_llskymap.png ). Best regards. Tobias
From ff382103981d27a5470eecf727fe962208a505e6 Mon Sep 17 00:00:00 2001
From: Tobias Winchen <winc...@physik.rwth-aachen.de>
Date: Wed, 25 Jan 2012 09:14:12 +0100
Subject: [PATCH 1/2] Added test cases
---
examples/allskymap.py | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/examples/allskymap.py b/examples/allskymap.py
index 1dc32b0..b06d70b 100644
--- a/examples/allskymap.py
+++ b/examples/allskymap.py
@@ -377,6 +377,14 @@ if __name__ == '__main__':
# lower right:
poly = map.tissot(185, -40, 10, 100)
+ #center
+ poly = map.tissot(0, 0, 10, 100, lw=1, color='m')
+ poly = map.tissot(0, -30, 10, 100, lw=1, color='m')
+
+ # poles
+ poly = map.tissot(120, -83, 10, 100, lw=1, color='m')
+ poly = map.tissot(0, 84, 10, 100, lw=1, color='m')
+
# Plot the tissot centers as "+" symbols. Note the top left symbol
# would cross the limb without the clip_path argument; this might be
# desired to enhance visibility.
--
1.7.8.3
From 1dbabb94b26b157e35b9500fadc3681642433c3a Mon Sep 17 00:00:00 2001
From: Tobias Winchen <winc...@physik.rwth-aachen.de>
Date: Wed, 25 Jan 2012 11:58:26 +0100
Subject: [PATCH 2/2] Fix for polar regions and regions crossing zero meridian
---
examples/allskymap.py | 58 +++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 56 insertions(+), 2 deletions(-)
diff --git a/examples/allskymap.py b/examples/allskymap.py
index b06d70b..ff93cc7 100644
--- a/examples/allskymap.py
+++ b/examples/allskymap.py
@@ -251,10 +251,15 @@ class AllSkyMap(Basemap):
returns a list of matplotlib.patches.Polygon objects, with two polygons
when the tissot crosses the limb, and just one polygon otherwise.
"""
-
+
+ #only use modified version if we are in a critical region
+ if ((self.east_hem(lon_0) and self.east_hem(lon_0+radius_deg)) or (not self.east_hem(lon_0) and not
+ self.east_hem(lon_0-radius_deg))) and abs(lat_0) + radius_deg <90:
+ return Basemap.tissot(self,lon_0,lat_0,radius_deg,npts,ax=None,**kwargs)
+
# TODO: Just return the polygon (not a list) when there is only one
# polygon? Or stick with the list for consistency?
-
+
# This is based on Basemap.tissot, but addresses a limitation of that
# method by handling tissots that cross the limb of the map by finding
# separate polygons in the eastern and western hemispheres comprising
@@ -268,6 +273,55 @@ class AllSkyMap(Basemap):
delaz = 360./npts
az = az12
last_lon = lon_0
+
+ #handling of the poles
+ if (abs(lat_0) + radius_deg >= 90 ):
+ # Use half of the points for the part inside the map, the
+ # other half of the points is at the map border
+ lats = zeros(npts/2)
+ lons = zeros(npts/2)
+ for n in range(npts/2):
+ az = az+delaz *2
+ lon, lat, az21 = g.fwd(lon_0, lat_0, az, dist)
+ lons[n] = lon
+ lats[n] = lat
+
+ a = list(argsort(lons))
+ lons = lons[a]
+ lats = lats[a]
+ x1,y1 = self(lons, lats)
+
+ # Half of the remaining points are used on eastern and
+ # western hemisphere.
+ N = npts/4
+ segs = []
+ dL = (90-abs(lats[0]))/ (N-1)
+ r = range(N)
+
+ # For the south-pole the order of points is changed to plot
+ # the correct polygon
+ if lat_0 < 0:
+ r.reverse()
+ segs.extend(zip(x1,y1))
+ #First Half of the map border
+ x, y = self(-180 * sign(lat_0) *ones(N) , sign(lat_0)* (90 - array(r)* dL) )
+ segs.extend(zip(x,y))
+
+ if lat_0 > 0:
+ segs.extend(zip(x1,y1))
+
+ #Second half of the map border
+ r.reverse()
+ x, y = self(180 * sign(lat_0) *ones(N) , sign(lat_0)* (90 - array(r)* dL) )
+ segs.extend(zip(x,y))
+
+ #z = array(segs)
+ #self.plot(z[:,0], z[:,1])
+ poly = Polygon(segs, **kwargs)
+ ax.add_patch(poly)
+ return [poly]
+
+
# Note adjacent and opposite edge longitudes, in case the tissot
# runs over the edge.
if start_hem: # eastern case
--
1.7.8.3
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