I have to admit, I have no idea about how the Brazilian polyconic system
works.
But your excerpt from mapinfow.prj (supplied by MapInfo) has me wondering
about a few things.
"Polyconic" really refers to two different things:
1. A continuous pseudo-conic projection that uses a different cone
for each parallel of latitude.
2. A multi-part system of projections (using SOME OTHER conic
projection algorithm) with fixed standard parallels.
Presumably, the "polyconic" projection algorithm that appears in the
MapInfo Reference as code 27 is the continuous version, as a multi-part
system would use the code for the other conic projection algorithm.
But we have:
> "--- Brazil - Polyconic systems ---"
> "Brazil - UF:AC (South American 1969)", 27, 92, 7, -70, 0, 0, 0
> "Brazil - UF:AL (South American 1969)", 27, 92, 7, -37, 0, 0, 0
> "Brazil - UF:AM (South American 1969)", 27, 92, 7, -65, 0, 0, 0
etc. In other words, a multi-part system using the *continuous* Polyconic.
The only difference between the zones is the origin latitude, meaning
all of the zones differ from each other only by a translation along the Y
axis.
In the long run, I think that mapinfow.prj defines the Brazilian polyconic
system incorrectly, and you will need to find out the corrrect projection
parameters from the Brazilian government.
If you have a paper map that shows meridians, you can perform a quick
experiment: Place a straight edge on the map, aligning the point where
one meridian enters from the top of the map and the point where the same
meridian leaves the bottom of the map. If the meridian is *curved*, you
have a continouous Polyconic. If it's straight, then you have a standard
conic projection labeled "polyconic" because it's part of a system.
If I embarrass myself with my musings, then so be it.
HTH
Spencer
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