[ptx] difference between rectangular and cylindrycal pano

[Jean-Luc Coulon (f5ibh)]

Thank you for all these informations.
This clarify a lot the thigs

Regards

Jean-Luc

Le 29.10.2004 05:12:42, Rik Littlefield a écrit :
> Marek,
> 
> PTviewer assumes that its input image is equirectangular projection,  
> possibly less than full spherical 360x180 degrees.  For partial panos  
> with small fov, there is not much difference between equirectangular  
> and rectilinear or cylindrical, so visually it works OK to use those  
> with PTviewer also.
> 
> Whether you should use rectilinear or cylindrical for website and  
> printing depends on what you are trying to accomplish.  With  
> rectilinear, all lines that are straight in the world are also  
> straight in your picture, but you get severe distortion if you try to  
> go beyond roughly 120 degrees fov.  With cylindrical, the horizon and  
> verticals are the only straight lines in the world that end up  
> straight in your picture, but you can go up to full 360 degrees  
> horizontal.
> 
> Cylindrical and equirectangular have many of the same characteristics  
> -- up to a full circle around, vertical lines in the world are also  
> vertical in your picture, things near the poles get badly distorted.   
> The difference is that in equirectangular, you can go clear to the  
> poles and things near the poles get "squashed" vertically, where in  
> cylindrical they get "stretched" and you can go only about +-60  
> degrees vertically before distortion gets too much.  (PTViewer remaps  
> from equirectangular input to rectilinear on the screen, so when you  
> look up, you see an undistorted view of the stuff above you.)
> 
> For technical discussion and pictures using maps of the Earth, see


> http://mathworld.wolfram.com/EquirectangularProjection.html ,  
> http://mathworld.wolfram.com/CylindricalProjection.html, and  
> http://mathworld.wolfram.com/RectilinearProjection.html , which links  
> to http://mathworld.wolfram.com/GnomonicProjection.html .  (What  
> photographers call "rectilinear" projection, geographers call  
> "gnomonic".  It's not immediately obvious that gnomonic projection  
> maps lines that are straight in 3D to lines that are straight in the  
> map, but it does.)
> 
> --Rik

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