mayavi texture to span over full surface

Question

I want to do something similar to:3D terrain visualization with python and Mayavi2

As input I have an image (map) with a defined width and height in pixel. For this image / map I get the digital elevation model of the surface the image / map represents (extent). The extent consists of the min / max longitude and latitude values. For the elevation model I interpolate a grid with the same amount of values as the pixel of the image.

im # PIL Image object

pixel_x, pixel_y = im.size
ext = [lon_min, lon_max, lat_min, lat_max]

xstep = float(ext[1] - ext[0]) / float(pixel_x)
ystep = float(ext[3] - ext[2]) / float(pixel_y)     
X, Y = np.mgrid[ext[0]:ext[1]:xstep,ext[2]:ext[3]:ystep]
Z = griddata(coords, elevations, (X, Y), method='cubic', fill_value=-1)

From the X,Y,Z I plot the surface

surf = mlab.surf(X,Y,Z, color=(1.0,1.0,1.0)) 

Now I want to overlay the image over the surface:

img = image_from_array(np.array(im))
texture_img = tvtk.Texture(interpolate = 1)
texture_img.input = img

surf.actor.enable_texture = True
surf.actor.tcoord_generator_mode = 'plane'
surf.actor.actor.texture = texture_img

This gives me a result as in

Here I used the matplotlib lena version: lena.png

At the border the texture is repeated and not stretched over the whole surface area (as I would like). I would like to achieve that no pixel of the image is "repeated".

What can I do to prevent that the texture "overlaps" at the border?

I tried to normalize the X and Y values to be between 0 and 1, but this did not help.