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Dear sir:
        While I have never used software that allows use of a light pen on
screen, there is software out there that allows "heads-up digitizing" with the
mouse. I have used both CadCore by Hitachi which is available in DOS and Windows
versions, and is extremely easy to use, and I am currently using Intergraph's
I-Geovec, which is also dependant on having Bentley's Microstation as the CAD
engine and I-RAS B as the raster display software. Its a little more complex,
and I suspect a lot more expensive as well. Both work on the same principles:
they allow fully interactive, intelligent digitizing, or tracing of lines. You
can preselect a line type with attributes, feature code, Z-value etc. and pick a
line to trace on-screen. Depending on the parameters you have set up, the
software will then interpret a vector line through the raster image until it
reaches any point of confusion (end of line, gap, intersection etc.) and then
allow you to manually digitize a few point to clear the area of confusion, and
continue on its merry way. Success is very dependent on the quality of the
scanned image coupled with a wise choice of parameter settings. A lousy image
will simply take a lot of time consuming manual digitizing, and perhaps may be
better off digitized by tablet. Bad parameters will also result in lots of
confusion on the software's behalf, unwanted generalization, or inclusion of
rough image areas as zig-zags in the vector line. I have used Cadcore to
vectorize 1:10000 contour sheets (using just the contour plate separation-no
other linework) from Ontario, and been able to complete a sheet in half a day.
 
                                Good luck!
 
                                        Sean D. Smith
                                        Cartographer
 
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