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| Subject: | [gislist] dead reckoning and spherical trig |
| Date: |
04/05/2004 04:40:02 PM |
| From: |
Zane Crawford |
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Hi there, I was just wondering if anyone out there has experience with
"reckoning", calculating locations as one moves on the surface of a
sphere...
I'm modelling the formation of cracks in the ice shell of Europa (one of
Jupiter's icy moons) resulting from diurnal tidal stresses imposed by
Jupiter, and I need some way to figure out where the crack is
propagating to, given the stresses and where it starts... Basically I
know:
- initial lat/lon
- direction of propagation (azimuthal angle east from north)
- distance propagated (either decimal degrees or surface distance)
and I want to be able to calculate the location of the tip of the crack
after propagation has occurred.
The expression needs to be accurate for small distances (relative to the
size of Europa... radius 1569 km), and should be able to deal with
crossing the equator or prime meridian. It would be extra awesome if
someone had one that would work for non-spherical geoids.
I'm sure someone out there has this expression lying around... it
apparently exists as a funciton in the Matlab Mapping Toolbox (called
'reckon'). I've gone through the spherical trig from equations listed
in the USGS Map Projections book (using Mathematica) and it becomes an
unsightly mess.
Thanks in advance!
Zane
--
Zane A. Crawford zane@ideotrope.org
Amateur Human https://ideotrope.org
Boulder, Colorado __o
work : 303.492.6230 _`<,_ "Here we are, trapped in the
cell : 720.201.0751 (*)/ (*) amber of the moment. There
PGP : 0x55E0815F is no why."
-- Kurt Vonnegut
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