Converting ARC60 UTM --> WGS84 UTM - East Africa

Discussion created by makelmii on May 4, 2010
Dear list readers,

I work with East African data and I have a set of topographic maps I have registered as ARC60 UTM 37S (because the topo coordinates are given as these). I would now like to convert these to WGS84 UTM 37S, as most of our data is in this reference system. Straight forward up to here.

When I do the transformation, the toposheets that were connected to each other in ARC60, now have a gap of approx. 260m in N/S direction and approx. 80m in W/E direction. I've understood that this is the transformation difference between the reference systems.

My puzzle is, why don't the images all move in the same direction but leave these gaps?

And the number one question: how do I fix it?

One work-around I've tried already is to mosaic all the images together and then do the transformation. It works, but I would like to keep the images separate and surely there must be a better way of doing this.