determining aspect ratio and output map extents

[Nathan Vander Wilt]

We are hoping to use MapServer to automate the rasterization of a  
whole stack of layers. We previously did this using ArcMap's image  
export, and although the process was fraught with peril, the program  
did allow us to export a world file giving the extent of the exported  
images, which we rely on in a later part of our process.

We've noted that the EXTENT set in the map file does not always match  
the output, because the output image extents also depend on the  
aspect ratio of the given SIZE.

Do the MapServer tools provide any method to determine an optimal  
aspect ratio for the SIZE so that the EXTENT set in the map file will  
match the extent of the output image after rendering?

And/or: Is there a way to query the coordinates of the output corners  
from a .map file, either via shp2img, the CGI or some other utility?

thanks,
-natevw