newb - calc'ing geotiff world file internals

[Mike Dee]

All,

First time dipping my toe in the GIS world after many years of wanting to
get into it.  Finally have a project that I can leverage with mapserver and
I'm immediately in over my head on trying to figure out what goes into the
TFW file.

I'm attempting to create a raster tile index with the images within
http://www.fs.fed.us/r5/stanislaus/maps/emigrant/ -- I've made a similar
layout of the larger images at
http://www.snfv.org/forum/schedule/em_map_big.html that I'm actually going
to be using the images from, the first link shows how the images are already
laid out in a tile like setting.

I've spent a couple of days digging around thru google trying to figure out
what the values inside the TFW file would equate to but I'm stumped.  How
would I figure out what the pixel width is for X & Y?  are the last 2 coords
in UTM?  I've read the HOWTO at
http://mapserver.gis.umn.edu/doc44/raster-howto.html but it doesn't go into
much detail, seems like it assumes that you know the values prior to writing
the TFW file.  I've also read thru the geotiff spec at
http://www.remotesensing.org/geotiff/spec/contents.html too but it didn't
help me either.

The project I'm starting would create a layer(s) on this map that would show
issues in the wilderness area such as wet trails, heavy mosquitos, trails
under repair, etc.

Thanks in advance

Mike