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
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