Re: Great Circle mapper

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         12 Oct 96 02:35:55 
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[This is drifting away from aviation -- is there any newsgroup
appropriate for maps and cartography?]

>I have seen (in a restaurant!) a large number of maps each of which
>was centered on a major world city and any straight line form which
>was a great circle.

That would be a map drawn using an orthographic projection, in oblique
form unless you center on a pole (polar) or the equator (equatorial).
The reference section of the Perry-Castaneda Library Map Collection
has a nice description of this and other projections -- look at

>   Does anyone know where I can buy such maps?

Polar ones shouldn't be too hard to come by, but finding good ones
based on arbitrary centers might be a challenge.

>   Does anyone know of any PC or workstation software that generates
>     such maps?

Some of the PC mapping software might be able to do this for you but
I don't know much about those packages.  For workstations, various
mapping tools can be found on the net but they're essentially kits,
with some scavenging needed to collect the data and glue everything
together, so you'd have to want these maps pretty badly.

The most popular WWW mapper, at Xerox, has several projections but
orthographic isn't one of them.  Several other WWW sites do support
this projection:
    This generates nice maps, but the interface wasn't thought out
    clearly for the orthographic projection -- you specify the top
    and bottom latitudes for the map, which is fine for rectangular
    or Mercator projections, but nearly meaningless for orthographic
    which most logically is based on a center point.  (The comments
    indicate the author is aware of the need for some interface
    enhancements.)  With some tinkering (try N=90, S=89.99, E=180,
    W=180 for the north pole, almost) you can get something decent.
    If your browser has Java support, the Cartography Applet is nice,
    if a bit slow to load, and it can do orthographic projections
    based on any center point you choose.
    This also works from a center point and can do orthographic maps.
    It's not as refined as the other two, but works reasonably well.

Karl Swartz	|Home
Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills