Digitizing

Hello--Wondering if anyone would know of software or procedure that
would allow digitizing a grid within a defined profile rather than an
XY rectangle? There is a lot of wasted time/motion in scanning into
the unneeded corner areas of the rectangle.
Perhaps a polyline of the profile could be exported DXF format and
then use Excel to merge the profile into the XY rectangle coordinates
and throwing out any XY coordinate that is outside the bounding
profile? This is over my head but thinking that a formula could be
used to examine each coordinate?
Or perhaps there is some software availabe to do this?
I'm digitizing archtop guitar plates which are highly contoured.
Any and all help is greatly appreciated.
Thanks
Nelson