[Geotiff] libGeoTiff GTIFKeySet in setting UTM bounds and scale....?

[pw]

Hello,

	I have been working on a program that maps data into UTM
projection. The mapping and geotiff creation part is now working
fine. The documentation for libgeotiff is rather confusing when
it comes to applying values for a projection to the output geotiff.
(After reading 
http://www.remotesensing.org/geotiff/spec/geotiff3.html#3.1.1
)
	Is ModelTiePointTag specifically for tiffs used by
Intergraph software, or is this an accepted standard for geotiff
images?
	Is ModelPixelScaleTag in meters or do I need to set
scale units with another tag?
	In  the geotiff spec, under 'Common Examples' 3.1.1 notes that the 
default is WGS_84 and meters for UTM. However, this does not indicate 
how to apply these values using libgeotiff, so I'm not
sure the information is even relevant to the library.
	It is also unclear what should be passed to the
GTIFKeySet function. Where is the full manual for the
library function set located?

Thanks for any insights,

Pete