Adrian, true, true .. well told story rhat ... thanks alot.
just to make a point: if bursa wolf parameters are missing, the parameters for an accurate ellipsoid shift are missing, so results will be (very?) inaccurate? kind regards ede -- > Hey, > > In the "for dummies" collection, "geodesy for dummies", from adrian, > will surely become a best seller :-) > > Michael > > Adrian Custer a écrit : > > >> On Mon, 2007-09-17 at 10:46 -0700, Jody Garnett wrote: >> >> >> >>> Edgar Soldin wrote: >>> >>> >>> >>>> just one question .. what is this bursa wolf parameter option? >>>> >>>> >>>> >> ... >> >> >> >> >>> My impression is that this is scary math I never quite understood. The >>> javadocs describe it all detail (and have links to papers etc..). >>> >>> >>> >> Well, Bursa was a 9 year old bicyclist from the Alps and...no, no, no, i >> lie. Actually it's not particularly scary math and quite easy to >> understand. All you really need to remember is that no one has ever been >> to the center of the earth. >> >> So everyone started surveying (mostly so the repressive central >> governments could exploit taxes from people and have lots of jolly wars >> where people could slog through the mud and kill each other so they'd be >> blood and suffering for all). Each group started from some random place >> on the surface of the earth. Right away, it becomes obvious to everyone >> that euclidean rules don't work so well. Some didn't care so much since >> taxes are basically arbitrary anyway and getting serious about it means >> you'd have to walk through fields and woods and get lots of mud on your >> shoes. Others kept at it and resorted to spherical geometry. Once you >> start doing that precisely and at continental scales you realize that >> doesn't really work either so you decide to try the next hardest thing, >> an ellipsoid of rotation. Now how do you know which one to choose? Well >> you pick one that minimizes your squared errors. All good and nice but >> (1) you are surveying the ground which is anything but an ellipsoid >> since it has all those ditches you keep falling into and that keep >> getting your clothes covered in mud and (2) you are not perfect >> especially with all that mud on your paper. So you have a bunch of >> errors. Well everyone that does this comes up with lots of different >> ellipsoids that work really nice for their data and everyone is sure >> they clearly have found the 'one true ellipsoid' and they decide to use >> that for all their work. Then everyone guesses where they actually are >> on each of their particular ellipsoids which involves lots of going >> outside at night and looking up from the mud at the stars. But then it's >> not like the edges of each survey was nice and level on these ellipsoids >> either --- think of the eastern USA. You can start nice and clean and >> warm and dry at an inn in Boston on the edge of the sea drinking clam >> chowder and having a good time but a few months later it will be bitter, >> bitter cold in that tiny town of Denver because you are somewhere like a >> mile high up in the air and you're wet and covered in mud from slogging >> through the plains in a snowstorm. So you've got a pretty good idea that >> your data is on a major slant but, well, you'll do your best to make up >> for it but it really doesn't help the effort any, especially what with >> all that mud that's still itching in your hair. So your errors may be a >> wee bit big but hey it's all right: it's good enough to wage lots of >> good wars with lots of mud and blood and to keep collecting lots of >> taxes so no one cares too much. >> >> Fast forward to more recent times where some people want to talk to lots >> of different governments and work with lots of different data. They take >> everyone's guess and try to line them up. Well it turns out, when you >> try to line everything up, that the center points of all the different >> ellipses aren't really the same points and even the orientation of the >> three axes are all a bit off because of how everyone guessed where their >> were on their ellipsoids. So now, to go from one data set to another so >> they line up "the best," you need estimates of how much to rotate each >> of the axes and how to shift the center point around; all this beyond >> even the obvious stuff of changing between the different definition of >> all those "one true" ellipsoids. >> >> When you do this mathematically, you need a bunch of parameters: these >> now have the names of the wolf and the bursa. Generally, you can only >> come up with good parameters if you have lots of data to compare and >> some good software to do the comparing. That's what the EPSG did for >> everyone. The guys in the pickup trucks that went out looking for oil >> kept falling into ditches along the way and getting mud on their faces >> but when they got back to the office they had a good sense of what lined >> up with what and could say: "yep, that hill there is the same as this >> squiggle here and there's this big ditch right here that cost us our >> third flat tire and..." So they collected as much data as they could and >> compared it and came up with a database of parameters by which you go >> > >from one data set to another. So that's it. That's why we use their > >> data; we don't have to fall in any ditches and can avoid getting mud on >> our clothes. They give us their parameters and we can mostly line up >> data from one survey against data from another. But you do need some >> good parameters because the earlier folk had a harder time of the mud >> and the data they created don't just line up the way we would like them >> to. >> >> Actually doing the math is a bit harder but the concept is pretty >> straight forward: geographic data all ultimately gets tied into points >> on the earth surface and that requires estimating where the points >> really are and how they line up on the estimated ellipsoid being used. >> That in turn means none of ellipsoids quite line up and we need >> parameters to move between them. >> >> --adrian >> >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by: Microsoft >> Defy all challenges. Microsoft(R) Visual Studio 2005. >> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >> _______________________________________________ >> Jump-pilot-devel mailing list >> Jump-pilot-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel >> >> >> >> >> > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2005. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Jump-pilot-devel mailing list > Jump-pilot-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel > -- public class WhoDidIt{ // A comment. I love comments private static Person sender; public static void main (String[] foo){ sender = new Person(); sender.setName(new String[]{"Edgar", "Soldin"}); Address address = new Address(); address.setStreet("Stadtweg 119"); address.setZip(39116); address.setCity("Magdeburg"); address.setCountry("Germany"); sender.setAddress(address); sender.setMobilePhone(" +49(0)171-2782880 "); sender.setWebSiteUrl(" http://www.soldin.de "); sender.setEmail(" [EMAIL PROTECTED] "); sender.setPGPPublicKey(" http://www.soldin.de/edgar_soldin.asc "); sender.setGender(true); System.out.println(sender.toString()); } } ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Jump-pilot-devel mailing list Jump-pilot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel
