Well thanks all for the answers! This is what I did:
- used r.profile to get (dist, elev) data from E-W profiles. - I didn't considered the elipsoid, I used and approximation to a sphere (to simplify my life :)) - from the total distance, I calculated the arc of curvature (theta) - now I have a spreadsheet with my data (gnumeric) - for the first point, I assigned a angular value of half the arc (theta/2) - for each subsequent point, I subtracted the value of (theta/n) - for n points in the profile - then I created another column, with the "elev" value times 100 (for vertical exaggeration) and added the radius of the Earth (6371 km) - finally I created a polar plot of the distance and angles. I not sure how "right" this is, but it seem to be a fair approximation. Carlos On Jan 15, 2008 3:30 AM, Hamish <[EMAIL PROTECTED]> wrote: > Carlos 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. > > > maybe a little work, but consider elevation as radius perturbation and > distance along transect as theta-angle, then draw a circle with the > relief shudder in it. ie like an AM radio wave. > > when that is working you can change the ideal circle to an ellipse of > appropriate bend for 3000km. > > > but probably it is better to just figure a way to calculate the > vertical distance between a chord connecting the two 3000km ends and > the circumference for each step along the transect. > > then add that distance to the elevation. > > > just an idea, > Hamish > > > > > ____________________________________________________________________________________ > Looking for last minute shopping deals? > Find them fast with Yahoo! Search. > http://tools.search.yahoo.com/newsearch/category.php?category=shopping > > -- +-----------------------------------------------------------+ 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. _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
