Re: [Matplotlib-users] images from data

[Eric F. <ef...@ha...>]

Michael V. De Palatis wrote:
> On Sat, Apr 29, 2006 at 08:41:48AM -1000, Eric Firing wrote:
> 
>>How easy it is to do this depends on your ascii file format, and how the 
>>data are organized in it.  Are the points in order? e.g.
>>
>>x0, y0, z00
>>x0, y1, z01
>>x0, y2, z02
>>x1, y0, z10
>>x1, y1, z11
>>x1, y2, z12
> 
> 
> This is precisely the ordering.
> 
> 
>>Are the values space-delimited, or comma-delimited, or in some other
>>format?
> 
> 
> The values are space-delimited. The way I am reading them in is with
> readline, then splitting the resulting string and appending to a list
> of x, y, and z values.
> 
> 
>>Is the grid uniform in the sense that all the x-intervals are the same 
>>and all the y-intervals are the same?
> 
> 
> Unfortunately, the grid is not uniform. From the responses I have been
> getting thus far, it's looking like this is going to be far more
> complicated than I had hoped...

It might not be complicated, but forget about using imshow--it is for 
image data, which are inherently evenly spaced.  Pcolor and pcolormesh 
don't have this limitation.  Note that Zij will give the color of the 
box with diagonal corners (Xij, Yij) and (Xi+1,j+1, Yi+1,j+1), so if Z 
has the same dimensions as X and Y, the last row and column will not be 
shown.  If your input data are intended to give the (x,y) positions of 
the centers of regions rather than the corners, then you will need to do 
some sort of regridding of Z, or shifting of your X and Y points, in 
order to get everything exactly right with pcolor and pcolormesh.

The attached script and sample data file show how you can put the data 
from your ascii file into X, Y, and Z arrays, and plot them using pcolor 
or pcolormesh.  This is for the simple case in which treating x and y as 
corners is good enough. Note that the grid does not have to form 
rectangular cells; they can be quadrilaterals.  I illustrated this in 
the sample file by shifting one point.

Eric