matplotlib-devel Mailing List for matplotlib

On Dec 7, 2007 6:02 PM, James Evans <jre...@ea...> wrote:
> There appears to be an issue with the agg backend with how it is drawing
> ellipses (or maybe it is how matplotlib uses agg), but the attached script
> shows how a point, which should be coincident with the center circle, but it
> is not. The second plot shows the same data, but using a custom (and much
> slower) algorithm for drawing the ellipses, where the point is properly
> coincident.
Thanks for the test case James -- I will try and sort this out ASAP.
Michael, do you see the same on the transforms branch? The branch is
on a newer version of agg so if not, perhaps it is a simple matter of
upgrading agg on the trunk. I'm travelling currently bt will be back
omorrow and ill look at this ASAP.
JDH

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# This example can be boiled down to a more simplistic example=0A=
# to show the problem, but bu including the upper and lower=0A=
# bound ellipses, it demonstrates how significant this error=0A=
# is to our plots.=0A=
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import math=0A=
from pylab import *=0A=
from matplotlib.patches import Ellipse=0A=
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# given a point x, y=0A=
x =3D 2692.440=0A=
y =3D 6720.850=0A=
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# get is the radius of a circle through this point=0A=
r =3D math.sqrt( x*x+y*y )=0A=
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# show some comparative circles=0A=
delta =3D 6=0A=
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##################################################=0A=
def custom_ellipse( ax, x, y, major, minor, theta, numpoints =3D 750, =
**kwargs ):=0A=
 xs =3D []=0A=
 ys =3D []=0A=
 incr =3D 2.0*math.pi / numpoints=0A=
 incrTheta =3D 0.0=0A=
 while incrTheta <=3D (2.0*math.pi):=0A=
 a =3D major * math.cos( incrTheta )=0A=
 b =3D minor * math.sin( incrTheta )=0A=
 l =3D math.sqrt( ( a**2 ) + ( b**2 ) )=0A=
 phi =3D math.atan2( b, a )=0A=
 incrTheta +=3D incr=0A=
=0A=
 xs.append( x + ( l * math.cos( theta + phi ) ) )=0A=
 ys.append( y + ( l * math.sin( theta + phi ) ) )=0A=
 # end while=0A=
=0A=
 incrTheta =3D 2.0*math.pi=0A=
 a =3D major * math.cos( incrTheta )=0A=
 b =3D minor * math.sin( incrTheta )=0A=
 l =3D sqrt( ( a**2 ) + ( b**2 ) )=0A=
 phi =3D math.atan2( b, a )=0A=
 xs.append( x + ( l * math.cos( theta + phi ) ) )=0A=
 ys.append( y + ( l * math.sin( theta + phi ) ) )=0A=
=0A=
 ellipseLine =3D ax.plot( xs, ys, **kwargs )=0A=
=0A=
=0A=
##################################################=0A=
# make the axes=0A=
ax =3D subplot( 211, aspect=3D'equal' )=0A=
ax.set_aspect( 'equal', 'datalim' )=0A=
=0A=
# make the lower-bound ellipse=0A=
diam =3D (r - delta) * 2.0=0A=
lower_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, =
edgecolor=3D"darkgreen" )=0A=
ax.add_patch( lower_ellipse )=0A=
=0A=
# make the target ellipse=0A=
diam =3D r * 2.0=0A=
target_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, =
edgecolor=3D"darkred" )=0A=
ax.add_patch( target_ellipse )=0A=
=0A=
# make the upper-bound ellipse=0A=
diam =3D (r + delta) * 2.0=0A=
upper_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, =
edgecolor=3D"darkblue" )=0A=
ax.add_patch( upper_ellipse )=0A=
=0A=
# make the target=0A=
diam =3D delta * 2.0=0A=
target =3D Ellipse( (x, y), diam, diam, 0.0, fill=3DFalse, =
edgecolor=3D"#DD1208" )=0A=
ax.add_patch( target )=0A=
=0A=
# give it a big marker=0A=
ax.plot( [x], [y], marker=3D'x', linestyle=3D'None', mfc=3D'red', =
mec=3D'red', markersize=3D10 )=0A=
=0A=
##################################################=0A=
# now lets do the same thing again using a custom ellipse function=0A=
=0A=
# make the axes=0A=
ax =3D subplot( 212, aspect=3D'equal', sharex=3Dax, sharey=3Dax )=0A=
ax.set_aspect( 'equal', 'datalim' )=0A=
=0A=
# make the lower-bound ellipse=0A=
custom_ellipse( ax, 0.0, 0.0, r-delta, r-delta, 0.0, color=3D"darkgreen" =
)=0A=
=0A=
# make the target ellipse=0A=
custom_ellipse( ax, 0.0, 0.0, r, r, 0.0, color=3D"darkred" )=0A=
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# make the upper-bound ellipse=0A=
custom_ellipse( ax, 0.0, 0.0, r+delta, r+delta, 0.0, color=3D"darkblue" )=0A=
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# make the target=0A=
custom_ellipse( ax, x, y, delta, delta, 0.0, color=3D"#BB1208" )=0A=
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# give it a big marker=0A=
ax.plot( [x], [y], marker=3D'x', linestyle=3D'None', mfc=3D'red', =
mec=3D'red', markersize=3D10 )=0A=
=0A=
##################################################=0A=
# lets zoom in to see the area of interest=0A=
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ax.set_xlim(2650, 2735)=0A=
ax.set_ylim(6705, 6735)=0A=
show()=0A=
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