 Need some advice | |
"Vic Fraenckel" <vfraenc1@nycap.rr.com> wrote in message news:<Wjj1b.1771$lk1.1472@twister.nyroc.rr.com>...
> I have implimented Vincenty's Direct and Inverse algorithms with both VB6
> and Delphi7. I have been distributing the code as open source.
>
> A user has pointed out a problem in the Inverse function which I had not
> noticed. The problem exists in both the VB6 and Delphi versions. I have
> been trying for several days to fix it. The essence of the problem is:
>
> given that point 1 is at a fixed latitude/longitude (I have been using
> 89N/0E) and compute a the length of a geodesic at say 20N/0E the length is
> 1,572,913.307 meters and when doing the same for 20S/0E (trans-equatorial)
> the length is the same. Obviously this is not correct. I believe the length
> of 89N/0 to 20N/0 is correct. I am using WGS84.
>
89N to 20N along a meridian is 69 degrees. 90 degrees along a
meridian is approximately 10,000km (the original definition of a
meter). So 69 degrees should be about (69/90)*10000=7667km. On the
WGS84 spheroid it will be slightly different - I get 7677.9056km using
Vincenty.
So where does 1572.913307km come from - or are we doing a different
problem?
Ed
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