nonlinear axes for imshow

Community matplotlib-users
1

Hello,

I have the following problem. I want the axes (only the y-axis, to be exact)
of a imshow() graph to be nonlinear. By default, the axis goes linearily
from 0 to (number of pixels). With the [extent] keyword, I can change that
to going linearly from (arbitrary start) to (arbitrary end). Now, I'd like
the axis to be dependend on a (bijective) arbitrary function, for example
y=p^2 (when p is the pixel number and y the y-axis coordinate).
How can I achieve this?
Thanks a lot, cheers

Thomas

···

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2

thkoe002 wrote:

Hello,

I have the following problem. I want the axes (only the y-axis, to be exact)
of a imshow() graph to be nonlinear. By default, the axis goes linearily
from 0 to (number of pixels). With the [extent] keyword, I can change that
to going linearly from (arbitrary start) to (arbitrary end). Now, I'd like
the axis to be dependend on a (bijective) arbitrary function, for example
y=p^2 (when p is the pixel number and y the y-axis coordinate).
How can I achieve this?
Thanks a lot, cheers

Thomas

See
http://matplotlib.sourceforge.net/examples/pylab_examples/image_nonuniform.html

Eric

3

Hi Eric,

thanks for the help, but this doesn't do what I want.
I don't want to change the image in any way, I just want the axes to have a
decreasing spacing. I made a small example with ms paint to clarify.

http://www.nabble.com/file/p25867951/axes.png

I could do this with ax.set_xticks() and ax.set_xticklabels(), but I was
wondering if there is a way that also changes the whole coordinate system
and not only the labeling. For example, the position of the mouse pointer
will not be shown anymore when I use custom ax.set_xticklabels().

Cheers

Thomas

efiring wrote:

···

thkoe002 wrote:

Hello,

I have the following problem. I want the axes (only the y-axis, to be
exact)
of a imshow() graph to be nonlinear. By default, the axis goes linearily
from 0 to (number of pixels). With the [extent] keyword, I can change
that
to going linearly from (arbitrary start) to (arbitrary end). Now, I'd
like
the axis to be dependend on a (bijective) arbitrary function, for example
y=p^2 (when p is the pixel number and y the y-axis coordinate).
How can I achieve this?
Thanks a lot, cheers

Thomas

See
http://matplotlib.sourceforge.net/examples/pylab_examples/image_nonuniform.html

Eric

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4

Hi Eric,

thanks for the help, but this doesn't do what I want.
I don't want to change the image in any way, I just want the axes to have a
decreasing spacing. I made a small example with ms paint to clarify.

http://www.nabble.com/file/p25867951/axes.png

I could do this with ax.set_xticks() and ax.set_xticklabels(), but I was
wondering if there is a way that also changes the whole coordinate system
and not only the labeling. For example, the position of the mouse pointer
will not be shown anymore when I use custom ax.set_xticklabels().

It depends on how far you want to go.

* Manually setting ticks is a easiest solution, I guess.

* The next step would be to create your custom tick locator & formatter

http://matplotlib.sourceforge.net/api/ticker_api.html

While this is not that difficult, you will need to spend some time.

* axes_grid toolkit has limited support for arbitrary coordinate system.

http://matplotlib.sourceforge.net/examples/axes_grid/demo_curvelinear_grid.html

* create your own projection.

http://matplotlib.sourceforge.net/devel/add_new_projection.html

Unless you're familiar with matplotlib and some of it internals, the
last two options is not recommended.
Regards,

-JJ

···

On Tue, Oct 13, 2009 at 2:48 AM, thkoe002 <thkoe002@...287...> wrote:

Cheers

Thomas

efiring wrote:

thkoe002 wrote:

Hello,

I have the following problem. I want the axes (only the y-axis, to be
exact)
of a imshow() graph to be nonlinear. By default, the axis goes linearily
from 0 to (number of pixels). With the [extent] keyword, I can change
that
to going linearly from (arbitrary start) to (arbitrary end). Now, I'd
like
the axis to be dependend on a (bijective) arbitrary function, for example
y=p^2 (when p is the pixel number and y the y-axis coordinate).
How can I achieve this?
Thanks a lot, cheers

Thomas

See
http://matplotlib.sourceforge.net/examples/pylab_examples/image_nonuniform.html

Eric

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developing skills, take BlackBerry mobile applications to market and stay
ahead of the curve. Join us from November 9 - 12, 2009. Register now!
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5

Hi JJ,

thanks a lot for your help. I think that
http://matplotlib.sourceforge.net/examples/axes_grid/demo_curvelinear_grid.html
has everything I need, I'll try it out. The coordinates given by the mouse
are off, but that seems to be the case even for the far more elaborate
"custom scale/projection" example ( examples/api/custom_scale_example.py ),
and it's not that important.

Thanks, cheers

Thomas

···

It depends on how far you want to go.

* Manually setting ticks is a easiest solution, I guess.

* The next step would be to create your custom tick locator & formatter

http://matplotlib.sourceforge.net/api/ticker_api.html

While this is not that difficult, you will need to spend some time.

* axes_grid toolkit has limited support for arbitrary coordinate system.

http://matplotlib.sourceforge.net/examples/axes_grid/demo_curvelinear_grid.html

* create your own projection.

http://matplotlib.sourceforge.net/devel/add_new_projection.html

Unless you're familiar with matplotlib and some of it internals, the
last two options is not recommended.
Regards,

-JJ

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