No subject

[Marilyn Ruiz]

>I'm digitizing a 1:500000 geology map which only has lat/lon coordinates
>ticked off on it (best I can find).  I've enlarged the map to facillitate
>digitizing.  Documentation for the map indicates that a 1:250000 quad map
>was used to compile during mapping.

>I'd like to digitize the map into a utm database location.  It has been
>recommended that I use the program m.ll2u to capture 6 utm coordinates from
>the lat/lon ticks to use as registration points (using the clark66 spheroid
>parameter).

>Can anyone offer some constructive criticism on this procedure and recommend
>what grid cell resolution (and dimension) I might use ??

>D. Youngs
>ASI, Las Cruces

What you will be doing is superimposing a rectangular grid over the
1:500,000 scale map. The UTM grid is intended for relatively large
scale maps. The USGS includes the grid on its maps of 1:250,000 or
larger. Ideally, you should adjust the geology polygons that are
drawn on the smaller scale map to match their true location on the
UTM grid. This could be done be redrawing the geology features
on a larger scale map with a UTM grid before digitizing or by
performing rubbersheeting on the vectors after digitizing. 

What you have proposed, however, could be an OK route to follow. Just
don't expect perfect allignment of the geology polygons with significant
topographic and hydrologic features produced at a larger scale 
that may also be in the GRASS database.

Marilyn Ruiz
University of Florida
ruiz at thales.geog.ufl.edu