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

[pw]

pw wrote:
> 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

(Pete Again)
As an adendum to this question:

I found the libgeotiff API notes:

http://www.remotesensing.org:16080/websites/geotiff/api/globals.html

and more specifically the notes for 'GTIFKeySet':

http://www.remotesensing.org:16080/websites/geotiff/api/geotiff_h.html#a24

There is some parameter name confusion in the documentation, which is
O.K. because I can figure out what matches what.

The docs for parameter 'count' say that :
QUOTE: "At this time all keys except for strings have only one value, so 
index should be zero, and count should be one."

Does this mean that I input my scales and UTM corner coords as a string
to GTIFKeySet ?

Thanks,

Pete