"left" and "right" sides of glacier boundaries

[Bruce Raup]

Hi all,

As you probably know, the GLIMS database provides for storing information
about what materials and features are on the left and right sides of
glacier boundary segments, and the GLIMSView program makes it fairly easy
to assign such attributes to digitized glacier boundaries.  However, the
definition of "left" and "right" hasn't really been firmly specified.

Ultimately, it would be nice if in GLIMSView, you could just click on one
side or the other and not worry about whether it is "left" or "right".
But we're not there yet.

I propose the following solution.  Since it might negatively impact those
who have already assigned such attributes, I want to get your feedback.  I
propose ordering all polygons to be in counter-clockwise order (interior
on left) at ingest time.  References to left and right would be according
to this vertex ordering.

GLIMSView currently outputs polygon segments with points ordered in the
direction of digitization, and can therefore output segments with
inconsistent direction when placed within the polygon.  My ingest software
already puts the segments together so that they match up end-to-end in a
consistent direction.  Now I'd like to make the handedness consistent too.

Comments?

Bruce

-- 
Bruce Raup                                               Phone:  303-492-8814
National Snow and Ice Data Center, U. of Colorado, 449 UCB, Boulder, CO 80309
http://cires.colorado.edu/~braup/