myk@vax5.cit.cornell.edu (11/21/90)
Can anybody tell me how to convert from metric map coordinates (X=nnnnnn, Y=nnnnnn) to latitude and longitude in degrees, minutes, and seconds? I tried to find a book that would include this, but apparently didn't look under the right subjects. Sounds like an esoteric question, so please send email rather than posting/followup. Thanks! -- Mike Oltz, Interactive Multimedia Group, Cornell University myk@cornella.bitnet
truett@cup.portal.com (Truett Lee Smith) (11/21/90)
If those coordinates are from a map like I had to generate some years ago, they are in meters from a reference longitude and the equator for a trans- verse Mercator projection, which is what the metric military maps use. So you have to know the reference longitude, whether or not the equator or some other crossing latitude is the zero in that direction, and the reference geoid to do the calculations. Turns out to involve elliptic integrals of standard form which can be found in the tables. Look in a book on the subject of "geodesy" for the details. Truett Smith, Sunnyvale, CA truett@cup.portal.com OR truett@tdd.sj.nec.com
tim@bea.hssc.scarolina.edu (Tim White) (11/21/90)
myk@vax5.cit.cornell.edu writes: >Can anybody tell me how to convert from metric map coordinates >(X=nnnnnn, Y=nnnnnn) to latitude and longitude in degrees, minutes, >and seconds? I tried to find a book that would include this, but >apparently didn't look under the right subjects. Sounds like an >esoteric question, so please send email rather than posting/followup. >Thanks! >-- >Mike Oltz, Interactive Multimedia Group, Cornell University >myk@cornella.bitnet Mike, read the fine print on your map and tell me the coordinate system being used. Most maps produced by the USGS will have multiple coordinate systems. It is common to see lat/long, state plane, and utm on a given map. If this is not labeled on the map, email and tell me roughly where it is and we will make an educated guess. By the way all these assume a U.S. map. Non - U.S. maps may require more work. For more info on conversions see the following U.S.G.S. publications by John Snyder. "Map Projections used by the U.S. Geological Survey". Geological Survey Bulletin 1532. ( This is the bible for cartographers, history, concepts, forward and inverse projections ). "Computer Assisted Map Projection Research". Survey Bulletin 1629. ( Never really used it much. Given to me on a visit to the survey ). "Map Projections - A Working Manual". U.S. Geological Survey Professional Paper 1395. ( LOTS of formulas ). Tim -- ============================================================================== Tim White University of South Carolina tim@otis.hssc.scarolina.edu Humanities and Social Sciences Laboratory (803)-777-7840 Columbia, S.C. 29208
landheim@bbn.com (Greg Landheim) (11/21/90)
In article <36117@cup.portal.com> truett@cup.portal.com (Truett Lee Smith) writes: >If those coordinates are from a map like I had to generate some years ago, >they are in meters from a reference longitude and the equator for a trans- >verse Mercator projection, which is what the metric military maps use. So >you have to know the reference longitude, whether or not the equator or some >other crossing latitude is the zero in that direction, and the reference >geoid to do the calculations. Turns out to involve elliptic integrals of >standard form which can be found in the tables. Look in a book on the >subject of "geodesy" for the details. > >Truett Smith, Sunnyvale, CA >truett@cup.portal.com OR truett@tdd.sj.nec.com I sent a direct email response to the originator of this question and suggested they were probably State Plane coordinates. I forgot that there is the system you are referring to. If the coordinates are in feet, they are probably State Plane. If meters, then they are probably in the system you are referring to. In the first case, any standard surveying book will give the equations and tables. In the second case, a geodesy text will probably have the answer. In either case, USGS can provide the information. Greg