true surface area
I.Warren
in the ArcGIS/ArcInfo environment? Several iterations of gridding seem
possible,but is this not a very common necessity for analysts? Please tell
me if I'm missing something very simple. I'm more an AV user with limited
ArcInfo experience,but I'm baffled that accomplishing this is not as simple
as going through the ArcInfo help file's surface functions.
Cheers,Ian
Paul Cooper
wrote:
I am not sure what you mean by "true surface area" - you should be
aware that map projections may be a significant confounding factor if
you are far enough from the region of true scale, unless you are using
an equal area projection. If you mean surface area corrected for
topographic surface, then I would approach it by generating a TIN for
the area concerned, using TINARC to generate polygons with slope and
aspect, unioning this with the polygon coverage required and then
computing the corrected area for each polygon (I think = planimetric
area / sin(slope)), doing STATISTICS to get the total area for each
input polygon and reattaching it to the input polygon cover using
joinitem.
This is not such a usual requirement as you think - most people only
deal with 2d planimetry, and go to great lengths to present data in
that form - the whole business of ortho-correction!
Paul
I.Warren
rather than sin I think. I had hoped that along with the ability to model
and represent surfaces would go a quick method to actually involve these
surfaces in area calculations. In areas with moderate to high relief,one
begins to add several square "units" to the planimetric area of any polygon.
I just imagined that there would be a tool(like those great avenue scripts
for AV-thanks to the authors) such that it would be quick and easy to get
the true/elevation corrected area of a polygon. Based upon the response to
my posts on this subject,maybe not so many folks get worried about being so
precise. I actually have a somewhat special situation in that the true
surface areas,in this instance,are within an open pit environment. Rock
mineralogy and chemistry in different areas are being modelled to predict
the chemistry of a future pit lake. Given the steep walls,there's much more
surface area available to contribute to the water chemistry than the simple
planimetric area. I'll likely just find an AV3.x machine to quickly do
this,though I think the university has done away with it. Perhaps it's
buried away in a Geography Department closet somewhere. Yet another great
avenue utility lost to us simple-minded,non-VB'ers.
Cheers,Ian
Paul Cooper
wrote:
You are right - I realized my error just after pressing the "send"
button! However, the procedure I suggested uses ARC/INFO Workstation,
not ARCView. I think you will find that Workstation ARC/INFO is more
powerful and flexible for this sort of calculation than ARCView or
ArcGIS. The procedure I outlined can be done in 5 or 6 ARC/INFO
commands.
Paul
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