Re: [Matplotlib-users] Rotating in imshow

[Thomas R. <tho...@gm...>]

Thanks to both of you for your help! I had spotted the transform  
argument in imshow, but didn't manage to find any information about  
how to use it. The Affine2D method looks like it will help, so I  
should be all set now.

Thanks!

Thomas

On Mar 13, 2009, at 5:20 PM, Andrew Straw wrote:

> Eric Firing wrote:
>> Thomas Robitaille wrote:
>>> Hello,
>>>
>>> I was wondering whether there is a way to rotate a grayscale/
>>> colorscale when using imshow.
>>>
>>> I have been using PGPLOT (a fortran/c plotting library) for many  
>>> years
>>> now, and the equivalent to imshow is called PGGRAY (or PGIMAG).  
>>> One of
>>> the arguments this function takes is a 6-element array TR which is a
>>> transformation matrix. From the PGPLOT documentation:
>>>
>>> "The transformation matrix TR is used to calculate the world
>>> coordinates of the center of the "cell" that represents each array
>>> element. The world coordinates of the center of the cell  
>>> corresponding
>>> to array element A(I,J) are given by:
>>> X = TR(1) + TR(2)*I + TR(3)*J
>>> Y = TR(4) + TR(5)*I + TR(6)*J"
>>
>> You could do this with the Axes.pcolormesh method.  You could start  
>> with
>> an unrotated grid (generated by meshgrid, for example), apply your
>> rotation, and use that transformed grid in pcolormesh.  Note that
>> pcolormesh requires the grid for the cell boundaries, not centers.
>>
>
> It should work with imshow() as well if you can set the affine  
> component
> of the transform to the desired values. Which it looks like you can in
> Affine2D(). (The affine matrix is the elements of TR listed above, it
> appears.)
>
> I have not tried to do this, however -- just saying that I think it's
> possible.
>
> -Andrew