[GRASS-dev] z-exag in wxnviz

Michael Barton Michael.Barton at asu.edu
Sat Nov 26 10:56:36 EST 2011

Thanks for the ideas Hamish. I'm pretty sure that there is a conversion from geographic coordinates in xyz to arbitrary screen coordinates in the OGL code section. I understand what Helena is hoping for, and this would indeed be the ideal. To me, this 'natural' ratio between xy and z should have a z-exag value of 1.0. I have tried to estimate this in the wxPython code, but it is a rough hack and the calculation really should take place in the conversion code for OGL, not in instantiating the slider code where I put it.

C. Michael Barton
Director, Center for Social Dynamics & Complexity 
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University

voice: 	480-965-6262 (SHESC), 480-727-9746 (CSDC)
fax:          480-965-7671 (SHESC),  480-727-0709 (CSDC)
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu

On Nov 25, 2011, at 11:36 PM, Hamish wrote:

> Helena wrote:
>> - in wxnviz to avoid the very small zexag for latlong,
> another idea for lat/lon z-exag: just figure out what is 20-25% of the canvas height (or ~15% of the north-south image width),
> and work backwards from there, rounding to the nearest nice
> round number.
> I don't know if there is any real way to escape from x:y:z ratios
> of 1 : 1 : 1/(1852*60), as anything other than that is numerically
> synthetic. if taking up the 1:cos(lat) aspect ratio adjustment
> perhaps rather than converting the elevation data to degrees,
> we could convert the ew, ns to "meters" to get ratios of
> 1852*60*cos(lat): 1852*60 : 1 as the cheap and dirty projection.
> for global lat/lon views you probably wouldn't want to do that
> though.
> Hamish

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