Sunburned Surveyor a écrit : > As surveyors we always hit local control monuments to calculate a > "best fit" datum transformation. This is neede because "one size fits" > all transformations between horizontal datums in the states aren't > always precise. This is especially true when moving from historic > datums to modern datums. I think this is what Michael is describing > Right > I must note that a projection library will not be able to completely > solve the transformation precision problems. At some point, when we > start talking about hundredths of a foot (at least in the USA) you've > got to do a surevy for each site. > Yes, it seems that different approaches exist, depending on the country size, the existing terrestrial geodetic network...
Michael > The Sunburned Surveyor > I'm on the way of writing a new library for coordinate transformation, > and I'm interested by your experience, as my goal is to manage properly > 3D and grid-based transformations, not only projections and BW > transformations. > > On Fri, May 2, 2008 at 7:41 AM, Michael Michaud <[EMAIL PROTECTED]> wrote: > >> Hi Peppe, >> >> As you mention, bursa-wolf transformation is not always enough to make >> precise transformation between old local reference system and new >> spatial reference system. >> The advantage is that it relies on a set of only 7 parameters and a well >> known algorithm. >> To do more precise transformations, countries often use grids to "adapt" >> the BW parameters locally or to apply corrections on the results. >> In France, if old system coordinates are transformed towards the new >> system with a BW transformation (indeed a simple translation), one get a >> precision of 1-2m (5m at worst), which is not that good. >> It is now recommended to use a grid to interpolate precise parameters >> which makes it possible to get a precision of a few centimeters. >> I don't know what is the system used in USA, but I know that Canada and >> Australia also use grid based transformations (or corrections?) based on >> NTV2 grid format. >> I'm on the way of writing a new library for coordinate transformation, >> and I'm interested by your experience, as my goal is to manage properly >> 3D and grid-based transformations, not only projections and BW >> transformations. >> >> OJ warping tool : you did an interesting remark about using warping tool >> to calculate local parameters. In the cases I know, precise parameters >> are interpolated on a regular grid, which is enough to have a good >> precision. Using another type of interpolation (with warping tool) may >> be useful if BW parameters are given for some random places. Is this the >> case for Italia ? Are BW parameters associated to a precise place or to >> regions ? >> >> The error you oberved between WGS84 and ED50 is very important. I >> checked the BW parameters recommended in France between those systems, >> and I found values which are about half the error you observed. Did you >> make sure that you applied the transformation in the right direction >> with the right sign ? >> >> Michaël >> >> Giuseppe Aruta a écrit : >> >> >>> Hi, >>> I did a test with the CTS plugin. >>> As control I used Taspunto, a software for Italian coordinate >>> transformation edited by Italian government. This software doen't use >>> formulas for transformation but on a grid of points (1500) in the >>> Italian territory and surroundings. It is considered to give an >>> accuracy of less than 1 metre. >>> Finally, opening all files with OJ and using Edgar plugin, I was able >>> toI define that EPSG parameters for helmet transformation gave an >>> error between 0.5-2 metres on mainland (continental Italy). Close to >>> easter side of Italy (Puglia) the error is almost of 8 metres. >>> Now 0.5-2 metres is more than acceptable, since EPSG spec gave an >>> accuracy of 4 metres. >>> I think that Edgar plugin works, at least between WGS84 and ROMA40. >>> So I wiull prepare an (un)official config file for Italian >>> transformation with the BW par. 1) Italy mainland, 2) Italy Puglia, 3) >>> Italy Sardinia and 4) Italy Sicily. >>> Nothing to do between WGS84 and ED50, the error is still of 400-600 >>> metres (any idea?) >>> >>> Regards >>> >>> Peppe >>> */Giuseppe Aruta <[EMAIL PROTECTED]>/* ha scritto: >>> >>> Hi all, >>> working around Edgar Soldin's Coordinate transformation plugin I >>> finally reached the (un)-famous problem of setting Bursa-Wolf >>> parameters (BW) for the tranformation between different >>> datum/projections. >>> I realize that the problem is not so simple as it is shows: >>> 1) despite the EPSG official archive on net >>> (http://www.epsg-registry.org/) and other informations, there is >>> no unique BW parameters even between the same transformation. >>> For instance, searching on EPSG register, EPSG1660 (transformation >>> from Italian ROMA40 to WGS84) I had the official parameters for >>> Italy mainland with a maximum error of 4 metres. >>> Well, I tested these parameters in some places "mainland" in >>> Italy, I had an errror even of 60 metres, for instance, in >>> Southern Italy >>> More than this I discover that some regions/areas defined their >>> own parameters. >>> This happens becaue the transformation between ROMA40, ED50 e >>> WGS84 is not correlated by geometric relations or simple >>> math but by comparing coordinates of some points within different . >>> >>> >>> The resault is this: >>> >>> Edgar's plugin works fine but people need to know the BW >>> parameters for the area of their interest. And sometimes this is >>> not easy to do..... (in respect to EPSG, geotools, etc). I image >>> this is a common problem in Europe >>> >>> ************************************************************ >>> >>> I will go anyway to write the tutorial page about projections on >>> wiki since this could be useful for who is interested. I will also >>> put on wiki some modified cs.conf (configurations) files >>> optrimized for local transformation (Umbria-Tuscany, South Tyrol >>> and Campania-Basilicata). >>> Note that there is no problem with transformation between crs that >>> don't BW parameters (eg. WGS84 to WGS84/UTM..) to be used for GPS >>> fanatics! >>> >>> ********************************************************** >>> The bulk of my letter is the follow notes: >>> Since OpenJUMP has some warping tools (Warp and even New affine >>> transformation). Is it possible to calculate local Bursa-Wolf >>> parameters using these tools on some reference points? Does >>> somebody thought about before? >>> This probabily could be an interesting area of research (for >>> pratical usage) of OpenJUMP: A way or a plugin that calculate >>> local Bursa Wolf parameters. >>> >>> I pass these questions expecially to Europian collugues since this >>> maybe is acommon pronblem: Gauss (Kruge, Boaga, etc) vs WGS84 or >>> ETRS89 >>> >>> *************************************** >>> >>> Regards and thanks for the answers >>> >>> Peppe >>> >>> ------------------------------------------------------------------------ >>> Tante idee per la salvaguardia del pianeta su >>> Yahoo! for good >>> >>> <http://us.rd.yahoo.com/mailuk/taglines/isp/control/*http://us.rd.yahoo.com/evt=52436/*http://it.promotions.yahoo.com/forgood/environment.html>.------------------------------------------------------------------------- >>> This SF.net email is sponsored by the 2008 JavaOne(SM) Conference >>> Don't miss this year's exciting event. There's still time to save >>> $100. >>> Use priority code J8TL2D2. >>> >>> http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone_______________________________________________ >>> Jump-pilot-devel mailing list >>> Jump-pilot-devel@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel >>> >>> >>> ------------------------------------------------------------------------ >>> Tante idee per la salvaguardia del pianeta su >>> Yahoo! for good >>> <http://us.rd.yahoo.com/mailuk/taglines/isp/control/*http://us.rd.yahoo.com/evt=52436/*http://it.promotions.yahoo.com/forgood/environment.html>. >>> >>> ------------------------------------------------------------------------ >>> >>> ------------------------------------------------------------------------- >>> This SF.net email is sponsored by the 2008 JavaOne(SM) Conference >>> Don't miss this year's exciting event. There's still time to save $100. >>> Use priority code J8TL2D2. >>> http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone >>> ------------------------------------------------------------------------ >>> >>> _______________________________________________ >>> 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 the 2008 JavaOne(SM) Conference >> Don't miss this year's exciting event. There's still time to save $100. >> Use priority code J8TL2D2. >> http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone >> _______________________________________________ >> 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 the 2008 JavaOne(SM) Conference > Don't miss this year's exciting event. There's still time to save $100. > Use priority code J8TL2D2. > http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone > _______________________________________________ > 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 the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Jump-pilot-devel mailing list Jump-pilot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel
