D'Arcy, There are just a few public-access sites that have more or less "original" data on various datums. The most comprehensive data set is that of the U.S. military. With regard to that, when you go to the http://www.nima.mil site, there are a variety of documents that you can download as well as software. For instance, Technical Report TR8350.2, Third Edition, 4 July 1997, "Department of Defense World Geodetic System 1984" lists all of the datum relations that are unclassified and currently available from the U.S. military. It is 170 pages long and is available free for downloading in Adobe Acrobat ".pdf" format. (There is also a link to the Adobe site for those users that do not have a copy of the free Acrobat program that runs on Windows95/98/NT.) Printouts on a laser printer are gorgeous. An item usually ignored by most people (from my observations), is that this reference work gives the accuracy estimators of the transformation parameters. There are many places in the world where 3-parameter datum shift values are given and the geocentric components are +/- 25 meters in X, and in Y, and in Z! When you do a three-dimensional solution for the Pythagorean Solution, that equates to 57+ meters on the ground! I commonly see comments on the "net" to the effect that, "Golly, my data doesn't seem to fit when I use __________ software package to do a datum shift ..." Well, guess where _________ software package got the parameters for the datum shift ... Yep, TR8350.2, and nowhere else. For the most part, there are no "secrets" regarding datum shift parameters when you consider 3-parameter solutions. The U.S. military has a long-established custom of calling that sort of thing a "Molodensky" 3-parameter datum shift" or on occasion, an "Abridged Molodensky 3-parameter datum shift" if the user is not interested in ellipsoid heights. This is so much gobbledygook. Without going into the subject deeply, this sort of transformation thing is intended for military users to sling bombs, missiles, napalm, and various related types of ordinance at the enemy. The military does NOT need hair-splitting accuracy to conduct war. Therefore, the National Imagery and Mapping Agency (NIMA) publishes only what is necessary to conduct its operations. In those cases that better accuracy is published, it is absolutely ALWAYS with the consent of that particular country. (Notice that you can get pretty good accuracy in the U.S., U.K., and Europe, but the parameters for the C.I.S. and many former members of the U.S.S.R. are good only to 25 meters in each geocentric component.) There are many, many places in the world that are too BIG to offer better accuracy that +/-25 meters for a single set of 3 parameters for a datum shift! Note that even in the U.S. there is an entire collection of parameters that you have to use depending on where you are in the country! For that reason, most people use the NA DCON technique in the U.S. rather than the military technique. The same sort of thing goes for Canada, and the Europeans are doing the same sort of things from country to country. TR8350.2 also has the Multiple Regression Equation (MRE) coefficients for various continental land masses such as Europe that will accomplish a transformation from the European Datum of 1950 to WGS84 with better accuracy than a simple 3-parameter datum shift. Note however, that NATO commanders have been warned not to use the MRE coefficients for naval artillery support applications because the reliablity of this method is seriously defficient! The moral of the story is that (the use of a) MRE is useful only in areas of "interpolation" and not in areas of "extrapolation." In the U.S., I think the fools and idiots in the U.S. Bureau of Land Management never were aware of this little "factoid" as applied to the lease blocks in the Gulf of Mexico. Such MRE coefficients are also available for Brazil, Argentina, Australia, etc. - all only suitable for use "onshore" and not for offshore or navigational applications. A secondary and VERY derivative source of miscellaneous datums is the European Petroleum Studies Group (EPSG) site hosted by PetroConsultants.com in Switzerland. This is a group of (European) oil companies that have gathered together and agreed to share some of their data. The majority of the data they have so graciously agreed to share is from TR8350.2 along with some parameters (mostly correct) regarding national Grid Systems. However, their data collection is woefully small because they only use data that is "open to the public domain and not proprietary." The data sets are copyrighted and are free to anyone that cares to download the stuff, but the proviso is that if one uses the stuff, one must credit the EPSG as the source. Their stated accuracy criterion is +/- one meter, and that is oftentimes met, but definitely not al ways met. As a result, I consider it interesting poison. I periodically download it and look at it, but I do not use it! The NIMA site also offers software for free. There is MADTRAN which implements all the published TR8350.2 datum shift parameters, along with another package called MUSE. MUSE is something else. It contains DCCP, a similar package to MADTRAN, but is for windows only, and various versions will work in WIndows95/98/NT, maybe Win3.1, and also for various flavors of UNIX such as Sun, Silicon Graphics, and whatever else I don't remember. MUSE, however, will also do lots of GIS types of displays that include vector and raster formats, but all peculiarly U.S. Department of Defense (and NATO) stuff. They (at present) could not care less about commercial GIS formats. Whatever other site you go to, unless it is a national government (like Australia) will only list the TR8350.2 data sets. There is nothing else offered anywhere for free. In regard to Grid transformation software, the free stuff is limited to the General Cartographic Transformation Package (GCTP) available in Fortran77 from the U.S. National Geodetic Survey sites as well as various U.S. Geological Survey sites. The U.S.G.S. also offers PROJ4, a version of GCTP that has been extended for a few foreign countries beyond GCTP as well as a number of additional "pretty picture" projections and all translated into ANSI "C" language. The National Geodetic Survey offers "NADCON" for free download which is a datum shift package among NAD27, NAD83, and NAD83 HARN. The U.S. Army Corps of Engineers runs the Topographic Engineering Center (TEC) at Fort Belvoir, Virginia. As a service to the Civil Works Division of the Corps of Engineers, they took the NADCON source code (trivial) along with the data files (really big deal), and wrote a Windows package that will also do State Plane Coordinate Transformations for every state and possession in the Un ited States! It is available for free and is called CorpsCon. Highly recommended! That is what I use to teach with. I consider CorpsCon the "cat's meow" in geodetic utility software for the United States. I am constantly amazed at the number of people that spend good money to buy "commercial" software that is no better than CorpsCon! The Canadian Government sells their version of CorpsCon. Different country, different way of doing things. Similar arrangements are to be found in England, Ireland, Northern Ireland, Belgium, etc. Outside of the U.S. and Australia, free is rare. Damned rare. The biggest free site in the world is http://www.nima.mil . That has about 110+ datums, and a few transformations beyond and including UTM. EPSG has some free data but no free software. I wrote a package a few years ago called "GRIDS 2.0". It was reviewed by John P. Snyder and he used it for his private consulting practice after he retired from USGS for a few years before he passed away. GRIDS 2.0 has information on 1,100+ datums and 3,200+ Grid systems used in absolutely every country in the world for the past 150 years. I sold a few copies to oil companies and some "special" agencies in the U.S. government (nobody else could afford it), and have not sold any since. I have been looking for software houses to license it from me and have been unsuccessful so far. I have decided that selling for volume is the only way to go. No more 5-digit prices. Anybody out there want to license a DLL that is a bazillion times better than anything else, including the U.S. military? $100 per copy? (minimum 10 licenses) Anybody? Hello? Miscellaneous datums? You betcha! Read my columns on Grids and Datums at: http://www.asprs.org/resources.html Cliff 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 Facsimilie: (504) 280-7095 >>>>>>>Business phones (504) 443-2355 or (504) 286-1200<<<<<<< -------------------------------------------------------- ----------------------------------- On Tuesday, 29 June, 1999 6:02 PM, D'Arcy Emery [SMTP:[EMAIL PROTECTED]] wrote: > Hi: > > Would anyone happen to know where I could get numeric > data on the various geodetic datums? > > Thanks Very Much, > > --D'Arcy > > ------- > Si Deus pro noblis quis contra nos? > HomePage: http://www.APlusAdmiralty.com > [EMAIL PROTECTED] > > ********************************************************** > ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
