From: Michael G. (adv) <ad...@md...> - 2007-01-10 12:18:17
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Daniel M. German wrote: > 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. Its called every time but in the paramcheck-function there is an if: - if formatparamcount == 0 (no parameters are given) then they are set to default values (0, 60). - if formatparamcount == 2 (phi1 and phi2) then all the calculation is done. This results in 7 parameters. - if formatparamcount == 7 then nothing is done. - else an error is returned. So first time the function is called and the formatparamcount is set to 7 and the calculation is not done in any subsequent calls. > 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 Yes, I noticed that too and I don't know why this is. By multiplying phi and y with -1 you get the same results as in mathworld. > 3. What do you think should be the behaviour if only 1 parameter is > given? I would say that then phi1=phi2. Michael |