If I understand you correctly, you want to draw a topographic profile
superimposed on an arc representing the curvature of the earth? What
you want to do then is show the orthogonal distance of each sample
from the chord defined by the start and end point of profile. You can
try as follows but you'll have to work out the details;
1.) Plot a great circle line between your intended start and end points.
2.) Trace the path that the great circle line follows with r.profile
and have it save the results to an xyz file. (the inability to sample
along the great circle exactly will introduce some errors).
3.) Multiply z by 200 (note that to be technically correct you should
change your sampled elevations from orthometric to ellipsoidal, but
the magnitude of the errors introduced will likely be insignificant on
the overall scale).
4.) Convert your xyz values to ECEF.
5.) Now, the vector between your start and end points in the ECEF
coordinate system will represent a chord so a little trigonometry
applied to the problem will allow you to calculate the orthogonal
distance between the sample and the chord (ie, apply a rotation matrix
so that the chord will be coincident with the x-axis of your plot).
6.) Plot your new values in any plotting software.
Clear as mud? The explanation is a little spartan, but it should get
you started.
Cheers,
Mike
On 10-Jan-08, at 2:06 PM, Carlos Guâno Grohmann wrote:
Sorry for the OT, but can anyone point me some reference (paper, web,
etc) that explains how can I draw a topographic profile using the
Earth´s curvature? I am thiking about the output of r.profile (ascii,
distance from origin + elevation), in a section of about 3000 km, with
a vertical exaggeration of about 200 times.
tks!
Carlos
--
+-----------------------------------------------------------+
Carlos Henrique Grohmann - Guano
Geologist M.Sc - Doctorate Student at IGc-USP - Brazil
Linux User #89721 - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
_________________
"Good morning, doctors. I have taken the liberty of removing Windows
95 from my hard drive."
--The winning entry in a "What were HAL's first words" contest judged
by 2001: A SPACE ODYSSEY creator Arthur C. Clarke
Can't stop the signal.
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