Hi.

I've discussed this issue before, and have found a couple of approximate ways 
of doing distance calculations:-

1.  Calculate a Vincenty Distance (equivalent to the DistanceSphere) - I can 
let you have the code.  This one is pretty accurate.

2. I have a reprojection algorythm that's more approximate, but will work for 
any size of geometry.  You will just have to accept that you can't draw an 
sphere on a piece of paper and live with the approximation.  I use

X = 111230 * cosine(radians(latitude)) m /degree Longitude
Y = 111230 m /degree Latitude

to reproject based on the lon /lat of the geometry's centroid.

The driver for this requirement is when working with GPS systems 
internationally.  You can get into a real mess with regional datums.  Best to 
stick to lat /long.
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