[OSRS-PROJ] Horrors of the Internet
Gerald I. Evenden
gerald.evenden at verizon.net
Wed Feb 12 11:18:41 EST 2003
A few days ago I took up the seemingly minor task of installing
the Czech projection Krovak Oblique Conformal Conic in my version
of PROJ.4. There seemed to be documentation and benchmarks on
the net, so away we go.
Wrong!!! I have rarely seen a more screwed up mess. Some sites
had what on the surface seemed like a proper mathematical
definition of the projection. BUT, closer examination revealed
variables/constants appearing our of thin air and values computed
but never participating in the final solution. I even found a
FORTRAN program that successfully compiled and yielded results
comparing with other sources.
As a defining example that can be demonstrated here without
proper math display mode is one of the first computations in the
projection's initialization: The term is usually referred to a 'B'
B = sqrt( (1 + e^2 cos^4(phi_c)) / (1-e^2) )
Of course I was lured into coding from the nicely displayed
source but learned, after painful hours of debugging, that this
material was seriously flawed: The above expression that was
employed in the code was the improbable expression:
B = sqrt( 1. + (e^2 cos^4(phi_c))/(1-e^2) )
This just shows how much BS floats on the Internet.
My biggest question is: are the executable sources and example
numbers listed out there correct, irrespective of the documentation?
For example one site lists:
1 FI: 50 12 32.4416 LAMBDA: 16 50 59.1790 X:1050538.643 Y: 568990.997
2 FI: 49 50 35.7896 LAMBDA: 12 50 23.7895 X:1053301.049 Y: 859084.699
3 FI: 49 50 35.7896 LAMBDA: 22 19 38.8766 X:1117926.669 Y: 180241.362
4 FI: 48 38 23.4659 LAMBDA: 22 19 38.8766 X:1251684.182 Y: 184607.141
5 FI: 50 15 30.7008 LAMBDA: 17 25 51.1792 X:1049221.190 Y: 527189.195
6 FI: 50 12 32.4414 LAMBDA: 16 50 59.1790 X:1050538.649 Y: 568990.997
where FI and LAMBDA are respective latitude and longitude.
Oh yes, an example site where the impressive math display has many
holes in it is:
http://www.posc.org/Epicentre.2_2/DataModel/ExamplesofUsage/eu_cs34e2.html
It is interesting how often the same material appears on different
web sites where the local web master has not paid a bit of attention
to the contents of what he/she has copied. For shame!
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