ali_m ali_m - 5 months ago 20
Python Question

mayavi - setting the [x,y,z] extent of an image programatically

I have some data that consists of several 2D images that I would like to render in specific [x,y,z] positions relative to one another using

mayavi2 (v4.3.0)
.

From the documentation it seems that I should just be able to do this with
mlab.imshow()
. Unfortunately, mayavi throws an exception when I call
imshow
specifying the
extent
parameter (
AttributeError: 'ImageActor' object has no attribute 'actor'
).

I also tried setting the x,y and z data directly by modifying
im.mlab_source.x,y,z...
. Weirdly, whilst this correctly changes the x and y extents, it does nothing to the z-position even though
im.mlab_source.z
clearly changes.

Here's a runnable example:

import numpy as np
from scipy.misc import lena
from mayavi import mlab

def normal_imshow(img=lena()):
return mlab.imshow(img,colormap='gray')

def set_extent(img=lena()):
return mlab.imshow(img,extent=[0,100,0,100,50,50],colormap='cool')

def set_xyz(img=lena()):
im = mlab.imshow(img,colormap='hot')
src = im.mlab_source
print 'Old z :',src.z
src.x = 100*(src.x - src.x.min())/(src.x.max() - src.x.min())
src.y = 100*(src.y - src.y.min())/(src.x.max() - src.y.min())
src.z[:] = 50
print 'New z :',src.z
return im

if __name__ == '__main__':

# this works
normal_imshow()

# # this fails (AttributeError)
# set_extent()

# weirdly, this seems to work for the x and y axes, but does not change
# the z-postion even though data.z does change
set_xyz()

Answer

Ok, it turns out that this is a known bug in mayavi. However, it is possible to change the orientation, position and scale of an ImageActor object after it has been created:

obj = mlab.imshow(img)
obj.actor.orientation = [0, 0, 0]  # the required orientation 
obj.actor.position = [0, 0, 0]     # the required  position 
obj.actor.scale = [0, 0, 0]        # the required scale
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