Subject:
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Re: twisted map
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Wed, 5 Jun 2002 05:01:29 GMT
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Viewed:
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409 times
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In lugnet.off-topic.geek, Christopher Tracey writes:
> Mr L F Braun wrote:
> > It's a transverse projection, probably at 45º of rotation--it looks
> > like a Lambert, but without access to my Bugayevsky and Snyder [1] I
> > couldn't tell you what the exact variation is called. There are so
> > many names for so many slight variations of the mathematics that I
> > can't remember them all (and besides, my work usually involves UTM
> > and little else). But it was definitely rotated transversally before
> > the projection was calculated--that's the only way to get output
> > quite like that.
>
> I agree with your assessment that it is a transverse project, but I
> thought Lambert was only suitable for projections of a hemisphere? I
> could be mistaken though, it's been several years since I worried about
> projections and never did much serious work with anything bigger than a
> hemisphere and most the time i was worried about the US (1). I since
> gotten rid of most of my map projection books. oh well.
For hemispheric mapping, conic projections were generally used.
Lambert can be applied cylindrically, though:
http://aips2.nrao.edu/docs/memos/107/node3.html#SECTION00031300000000000000
Which gives the map severe t/b end compression. I'm not sure, again,
what the maths are that govern the original map Suz put up. There
are so many small variations of equal-area projections that I just
went with Lambert as being one of the best-known.
Of course the UTM is nice to use when you're anywhere near the equator.
Most of my work involving equatorial Africa (<10° N/S) therefore uses
it.
> Changing topics slightly, what are currently doing with mapping? Is it
> part of your graduate work? just curious... I've been doing a lot of
> current work with UTM and Stateplane in the past few months.
I deal with the history of cartography, specifically the history of
geodesy in Africa (arc of the 30th Meridian). In a sense projections
don't come into play except as authorities were concerned with the
computations and adjustments of the Arc for UTM projection use. The
arc, of course, was the provider of the primary datum used--it was
even a reference source for Hartebeesthoek94 and (IIRC) WGS84.
So I don't deal with map projections directly--I deal with the data
that are fed through the projection maths to get the maps. I'm heading
to SA on a Fulbright in October to get the African angle of this map
rendering--it should be very interesting.
> > For general information on transverse projections, see this:
> >
> > http://www.mapthematics.com/Essentials/Essentials.html
>
> great site-- really informative both for the newbie and 'enthusist'
I constantly learn more and more about cartography and surveying. It's
fun--I actually know how to use an 18th-C. theodolite now!
What do you do?
best
LFB
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Message has 3 Replies:
 | | Re: twisted map
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| (...) cool. very cool. (...) cool, i would occasionally go down to the museum at the USGS HQ in Virginia and examine the collection of historical survey devices. (...) Well, I first started work with mapping when I spent two years providing (...) (22 years ago, 5-Jun-02, to lugnet.off-topic.geek)
| | | Re: twisted map
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| (...) ~Such fun! For I live upon the oblate spheroid of Terra. (The geoid of Earth) [I learned something new today!] Oh, and the stuff about the rhumb line, or, loxodrome has some applications in stellar cartography and the continuum of space. =P (...) (22 years ago, 5-Jun-02, to lugnet.off-topic.geek)
| | | Re: twisted map
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| (...) I want to jump in here and mention my favorite projection; when I first saw the Peters map, it blew my mind. Check it out: (URL) a high schooler, it really opened my eyes. Why *do* we still use the Mercator projection? -John (22 years ago, 5-Jun-02, to lugnet.off-topic.geek)
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Message is in Reply To:
| | Re: twisted map
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| (...) I agree with your assessment that it is a transverse project, but I thought Lambert was only suitable for projections of a hemisphere? I could be mistaken though, it's been several years since I worried about projections and never did much (...) (22 years ago, 5-Jun-02, to lugnet.off-topic.geek)
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