Pablo, You will need a "Datum Shift" software package to do the transformations for you if you do not want them performed automatically with your GPS Receiver. The necessary transformation parameters for the geodetic systems you describe below are: da = +251 meters, df x 10^4 = +0.14192702, dX = +295 meters, dY = -173 meters, dZ = +371 meters. These parameters will allow you to go from WGS84 Datum to the PSAD56 (La Canoa) for Venezuela. Note that the accuracy of the shift parameters is plus or minus 9 meters in dX, 14 meters in dY, and 15 meters in dZ. That is based on a NIMA solution of 24 points in your country as supplied by La Cartografia Nacional to the Inter-American Geodetic Survey (NIMA). Be advised that the "signs" of each parameter I listed above is to go FROM the GPS satellite Datum TO the local classical Datum, "La Canoa," which is actually known as "PSAD56." The name, La Canoa is the Venezuelan town where the Astro/Geodetic Datum origin is located and the original spot where Dr. Romero determined the deflection of the vertical from a geodetic gravity survey (via helicopters) that he supervised in the early 1950's. For software to do this transformation outside of your GPS receiver, there is free software at the www.NIMA.mil site in two different forms: "MADTRAN" and "MUSE." The former is DOS command-line operation, the latter is fancy Windows operation. Both use the identical math to do this particular transformation. Both are free packages, the MUSE package requires that you "register" first to receive a password, and that is sent to you in seconds via e-mail. Once you are in "La Canoa," the most common Grid system used for (X,Y) coordinates in Venezuela is the UTM. Both MADTRAN and MUSE will do those transformations also. Note that the PowerPoint file you sent to me merely lists the ellipsoid and zone indicators for UTM. The specifier "CANOA" is really meaningless without proper validation of the character of your field data set and/or destination data set. I am assuming you acrually read the specifier off some published paper maps. At 1:50,000 scale military mapping of Venezuela, that makes sense. Furthermore, the accuracy level of the transformation parameters I gave above are suitable for use with a shirt-pocket GPS receiver and 1:50,000 maps. When you go to larger scale maps and you need greater corresponding accuracies, you will encounter the large number of coordinate systems in Venezuela that I previously wrote to you about. After that, I suppose it would be relatively simple to import the ASCII file of coordinates into MAPINFO or whatever GIS application package you are working with. If you are in Caracas, the staff geodesists at La Cartografia Nacional really know their stuff, and can help you in person or by telephone. Good luck, 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 On Wednesday, 09 June, 1999 2:06 PM, Pablo Alcazar [SMTP:[EMAIL PROTECTED]] wrote: > > Hi Cliff, > > I received your explication about Datum in Venezuela, > really the process > that I want is, if I have coordinates latitud, longitud > read with GPS in > WGS84 Datum how in Mapinfo automatily I can traslate the > information to my > Map that have La Canoa reference???? > > That�s all, if I can do that better, fine ok. > > Thank a lot > > > PD: information that I have about La Canoa is in the file > attach > << File: Datum.ppt >> ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
