Coordinate transformations and second axis

Hi Everyone,

after trying every example I could find in the documentation, gallery
and online I thought let's give the mailing list a try.
I have an image displayed with imshow.
I would like to display the pixel coordinates on the left y and bottom
x axis and the physical coordinates (in arcseconds) on the right y and
top x axis.
I tried it with twinx & twiny but then only a part of the image is
shown (image is in pixel coordinates), I also tried creating a new
axes object with ax2=plt.subplot(1,1,1, frameon=False) but then the
image is no longer shown (this might be a bug).
Is this possible with the current version (0.99) of matplotlib?

Kind regards,

Pim Schellart

As far as I know, there is no easy way to do that with mpl (especially
when image is involved).
You may manually add ticks and ticklabels (but without using set_ticks, etc).

If you're using 0.99 and later, you may use axes_grid toolkit, but it
has some cons. So, if you're going to use it, please read through the
documentation.

from mpl_toolkits.axes_grid.parasite_axes import SubplotHost
import matplotlib.pyplot as plt
import matplotlib.transforms as mtransforms

fig = plt.figure(1, (4,3))

ax = SubplotHost(fig, 111)
fig.add_subplot(ax)
ax.imshow([[1,2],[3,4]], origin="lower")

# transform from arcsecond to pixel
tr = mtransforms.Affine2D().translate(+1,+1).scale(2., 2.)
ax2 = ax.twin(tr)

plt.show()

Regards,

-JJ

ยทยทยท

On Wed, Oct 7, 2009 at 6:14 AM, Pim Schellart <p.schellart@...287...> wrote:

Hi Everyone,

after trying every example I could find in the documentation, gallery
and online I thought let's give the mailing list a try.
I have an image displayed with imshow.
I would like to display the pixel coordinates on the left y and bottom
x axis and the physical coordinates (in arcseconds) on the right y and
top x axis.
I tried it with twinx & twiny but then only a part of the image is
shown (image is in pixel coordinates), I also tried creating a new
axes object with ax2=plt.subplot(1,1,1, frameon=False) but then the
image is no longer shown (this might be a bug).
Is this possible with the current version (0.99) of matplotlib?

Kind regards,

Pim Schellart

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