Denise, The Chamberlin Trimetric Projection is an old thematic type of projection cooked up by the Chief Cartographer of the National Geographic Society back in the late 19th century. It looks really nice, but is a contrivance that attempts to display a map with features that are equally distanced from three separate points. Such a contrivance is impossible, but Chamberlin's attempt is a pretty good compromise. The Society still uses it, and it still looks really nice. That is a characteristic of most National Geographic Society Maps; not only are they accurate and useful, but they are actually framed and put up for display in people's homes - not just in offices. One problematic feature of this projection is that after it is drafted, color-separated and printed, the copyrighted map that is not supposed to be copied or put into digital form of any kind is downright difficult to digitize. That is, it's easy to digitize in terms of digitizer (x,y) coordinates, but the inverse computation to Latitude and Longitude is a "zinger." In the late John P. Snyder's work, "Map Projections - A Working Manual," U.S. Geological Survey Bulletin 1395, he lists it in two places in the index. The first time he covers it is in the section on pseudo conics, and specifically the ellipsoidal Bonne, the second time he mentions it in another context of contrived projections that give a hint. The old AT&T projection is, according to Mr. Snyder, an ellipsoidal projection that is roughly equivalent to the Chamberlin Trimetric. Although obscure, the math for that can be scrounged from old Bell Labs reports occasionally found in various libraries. The old cartographic trick of "paneling" for changing projections with a razor blade and paste could be used with a rubber-sheet transformation, but that is using brute force rather than mathematical elegance. Another thing you could do is go to the horse's mouth. Ask the National Geographic Society and see what they have to say. I imagine they are going to ask you why you want to know the mathematical details of one of THEIR projections ... Specifically with respect to MapInfo, I have no idea how to help you. My claim to fame is definitely NOT specific software commands or procedures. Good luck, -- Clifford J. Mugnier ([EMAIL PROTECTED]) The Topographic Engineering Laboratory Department of Civil and Environmental Engineering UNIVERSITY OF NEW ORLEANS New Orleans, Louisiana 70148 Voice and Facsimile: (504) 280-7095 ---------------------------------------------------------------------- Denise wrote: > > Hi > > I have seem numerous posts of yours on Mapinfo-L and > am hoping you can help me with information on this > projection. I have MapInfo, but it does not seem to > support this projection. Do you know how I would > go about finding more information on this projection > and then how I would use such info in MapInfo? > > Denise ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
MI Re: Chamberlin Trimetric Projection
Cliff Mugnier - University of New Orleans Mon, 2 Aug 1999 13:56:49 -0700
