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<DIV><STRONG><FONT face=Fixedsys size=2> When I
suggested a GLIMS button for reversing polylines and polygons,<BR>I was thinking
of Didger (vn3), in which directions are listed and the <BR>operation itself
takes two mouse clicks. Programming the operation is almost trivial, about three
lines of code, although determining the polarity is<BR>a bit (but not much) more
complicated. If anyone could make use of Fortran</FONT></STRONG></DIV>
<DIV><STRONG><FONT face=Fixedsys size=2>subroutines for these jobs they are
welcome to mine. (There are probably</FONT></STRONG></DIV>
<DIV><STRONG><FONT face=Fixedsys size=2>lots of such routines available,
however.)<BR><BR> Graham.<BR>
gcogley@<BR>
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.ca<BR><BR>
J. Graham Cogley, Ph.D., Professor of
Geography,<BR>
Department of Geography, Trent
University,<BR> 1600 West Bank Drive,
Peterborough, Ontario, CANADA K9J 7B8.<BR> Fax
705-742-2131. Tel 705-748-1011-ext1440. Email
gcogley@trentu.ca<BR>
http://www.trentu.ca/geography/glaciology.htm<BR><BR>----- Original Message
----- <BR>From: Fiona Cawkwell <BR>To: gcogley1@cogeco.ca ; glims <BR>Sent:
Tuesday, 01 March 2005 15:51<BR>Subject: RE: "left" and "right" sides of glacier
boundaries<BR><BR><BR>Bruce, Frank et al<BR><BR>in response to the very valid
practical issues Frank raised, there are tools <BR>in Arc that are capable
of indicating and reversing the direction of polyline <BR>and polygon themes
e.g. from the ESRI Arcscripts download site, for those <BR>people using ArcView,
line direction tool 'line_dir.zip' to identify current <BR>polygon direction,
and flip lines tool 'AS11421.zip' to change the direction <BR>of lines, with
comparable tools for those using ArcGIS; thus it is possible <BR>with this
software to delineate all exterior polygons in an anticlockwise <BR>direction
and interior polygons in a clockwise direction<BR><BR>best
wishes<BR><BR>Fiona<BR><BR><BR>>Hi Bruce and Co.<BR>><BR>>I full agree
with Frank opinion
(below)<BR>><BR>>Cheers<BR>>JPDedieu<BR>><BR>><BR>><BR>>xxxxxxxxxxxx<BR>>Hi
Bruce & Co.<BR>><BR>>I agree with using the hydrological convention
for assigning left and<BR>>right, using the opposite direction for internal
polygons and<BR>>follow the conventions given by the software. However, for
practical<BR>>reasons I want to add two points:<BR>><BR>>(1) If we
obtain glacier outlines automatically from satellite data<BR>>(what I thought
would be the 'normal' way of getting them ?) we will<BR>>have no circulation
direction of the outline. Using the 'gridpoly'<BR>>command in Arc/Info line
segments with 500 vertices each are created<BR>>and the respective polygons
have the value (label) from the original<BR>>Geo-tiff (which is 0 for
'glaciers' and 1 [or 255] for 'other'). In<BR>>order to allow calculation of
glacier areas the value 1 is set to<BR>>NODATA and in the attribute table the
item 'grid-code' is used for<BR>>glacier identification (-9999 for other and
0 for glaciers).<BR>><BR>>(2) The digitized Swiss glacier inventory from
1973 also did not use<BR>>any specific circulation. The discrimination of
glacier polygons from<BR>>internal polygons (rock outcrops) is made by manual
assignment of<BR>>a label to each glacier under investigation. As such, also
'problematic'<BR>>glaciers can be excluded from the statistical
analysis.<BR>><BR>>Best regards,
Frank<BR><BR>--------------------------------------------<BR>Dr Fiona
Cawkwell<BR>Post Doctoral Research Fellow<BR>Department of Earth and Atmospheric
Sciences<BR>University of Alberta<BR>Edmonton<BR>Alberta, T6G 2E3<BR><BR>tel.
780 492 7821<BR>fax. 780 492
2030<BR>fiona.cawkwell@ualberta.ca<BR></FONT></STRONG><A
href="http://www.ualberta.ca/~cawkwell/fiona_cawkwell.html"><STRONG><FONT
face=Fixedsys
size=2>http://www.ualberta.ca/~cawkwell/fiona_cawkwell.html</FONT></STRONG></A></DIV></BODY></HTML>