[ptx] difference between rectangular and cylindrycal pano

[Yili Zhao]

Hi Rik,
  How about the cubic projection? It seems that cubic projection has some relationship
with equirectangular projection?

Best regards,
Yili

	

======= 2004-10-29 11:12:42 Rik wrote:=======

>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
>
>spec wrote:
>
>> Hello,
>>
>> What exatly is the difference if I stitch pano as rectangular and 
>> cylindrical? As I understand it both are good to present a result as 
>> an image on a website or sth., and both are good to present pano as 
>> cylindrical pano in ptviewer. With equirectangular it's a whole 
>> different story - that I understand.
>>
>> -- 
>> Thanks,
>> Marek
>>
>>

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