## Re: [PanoTools-devel] Albers Equal Area Conic Projection

 Re: [PanoTools-devel] Albers Equal Area Conic Projection From: Daniel M. German - 2007-01-10 06:11:24 ```HI Michael, I finally got some time to add your code for the Albers Projection. Would you mind clarifing the following points? 1. I noticed that you use an unlimited number of "internal parameters", in this case 7. I suspect you do it for optimization purposes. Is the idea that some of these parameters can be computed once, instead of in each iteration? In the current implementation albersequalareaconic_paramcheck is called every time albersequalareaconic_erect is called. 2. You seem to interpret North and negative and South as positive angles. For instance, then I provide 0 60 (as in your example below) http://mdgrosse.net/pano/albers_0_60.jpg I get the opposite to what I would expect: http://mathworld.wolfram.com/AlbersEqual-AreaConicProjection.html To get that I need to use parameters 0, -60 http://mdgrosse.net/pano/albers_0_-60.jpg 3. What do you think should be the behaviour if only 1 parameter is given?=20 Thanks a lot! -- daniel =20 Michael> Hi Michael> The two parameters are the standard parallels in degrees. The r= ange is=20 Michael> from 90=B0 to -90=B0. Along these these parallels there is no a= ngular and no=20 Michael> scale distortion. The ordering of the parameters has no effect. Michael> Depending on phi1 and phi2 the shape of the projection is diffe= rently=20 Michael> curved. You can also make phi1=3Dphi2. When phi1=3Dphi2=3D90 th= en the=20 Michael> projection is circle. With phi1=3Dphi2=3D-90 the projection is = also a circle=20 Michael> but the other way round (i.e. 90: tripod is in the center, -90:= sky is=20 Michael> in the center). Michael> With phi1=3D-phi2 you get also a circle where the zenith and na= dir are=20 Michael> both located somewhere in the circle. phi1=3D90, phi2=3D0 gets = you a=20 Michael> half-circle. Michael> A few examples: http://mdgrosse.net/pano/albers_-90_-90.jpg http://mdgrosse.net/pano/albers_-90_0.jpg http://mdgrosse.net/pano/albers_0_-60.jpg http://mdgrosse.net/pano/albers_0_10.jpg http://mdgrosse.net/pano/albers_0_60.jpg http://mdgrosse.net/pano/albers_90_-90.jpg http://mdgrosse.net/pano/albers_90_0.jpg http://mdgrosse.net/pano/albers_90_90.jpg http://mdgrosse.net/pano/albers_9_10.jpg Michael> yuval levy wrote: >> --- "Michael Gross (adv)" wrote: >>> I wrote something about the changes in >>> http://mdgrosse.net/pano/albersequalareaconic.txt >>=20 >> thanks! to understand it better, I have a couple of >> questions: >>=20 >> P"60.0 20.0" >>=20 >> are these the two standard parallels? >> ? >>=20 Michael> ---------------------------------------------------------------= ---------- Michael> Take Surveys. Earn Cash. Influence the Future of IT Michael> Join SourceForge.net's Techsay panel and you'll get the chance = to share your Michael> opinions on IT & business topics through brief surveys - and ea= rn cash Michael> http://www.techsay.com/default.php?page=3Djoin.php&p=3Dsourcefo= rge&CID=3DDEVDEV Michael> _______________________________________________ Michael> PanoTools-devel mailing list Michael> PanoTools-devel@... Michael> https://lists.sourceforge.net/lists/listinfo/panotools-devel -- Daniel M. German "You could wind up belivin'=20 that paradise is nothin' more than a feelin' Marillion -> that goes on in your mind." http://turingmachine.org/ http://silvernegative.com/ dmg (at) uvic (dot) ca replace (at) with @ and (dot) with . =20 ```