[Qgis-developer] Fwd: Re: Datum Transformation - parameters for mainland Portugal

Fri Jun 20 01:08:57 PDT 2014

-------- Original Message --------
Subject: 	Re: [Qgis-developer] Datum Transformation - parameters for 
mainland Portugal
Date: 	Fri, 20 Jun 2014 09:35:00 +0200
From: 	Marco Hugentobler <marco.hugentobler at sourcepole.ch>
To: 	Pedro Venâncio <pedrongvenancio at yahoo.com>

Hi Pedro

Added two ntv2 entries and updated two entries, hope it is correct now.

I still feel uncomfortable to delete / update towgs84 entries in the 
qgis db only. I'm concerned this will get a mess over time if there are 
lots of updates (and the qgis.db is synchronized during install with the 
gdal table).
If the updates are very important, I'd suggest the Portuguese user group 
to provide a modified copy of srs.db for people to download.

>However I came across something quite odd. In the Datum Transformation window, automatically arise some strange transformations (red in the imagehttp://goo.gl/iIWOuw). These transformations give huge errors, and I do not >understand what they represent.

QGIS reads all possible combinations to get from one datum to the other. Seems to me these towgs84 transformations are all present in the transformation table (though I don't know the geographical crs related to 30004. Is it 4258?)

 >Regarding NTv2 grids (http://goo.gl/jDhxJB) I have another doubt here. 
On Linux, these files are placed in /usr/share/proj. On Windows, using 
the OSGeo4W installer, they are >placed in ..\OSGeo4W64\share\proj. With 
QGIS standalone, they are placed at ..\Program Files\QGIS 
Valmiera\share\proj. There is no possibility of copy the grid files, 
 >automatically during the installation? This will make it easier for 
less experienced users.

Maybe it could be done in the packaging (location is system dependent 
and there is not proj function call to get the right location).
Budling ntv2 files with the application is a frequent request. We can 
discus thiss further after the release. Problems I see are:
- too large install package if lots of files are present
- requires to check every file license

Problem 2 can easily be solved if a volountear steps up for maintaining.

Regards,
Marco

On 18.06.2014 15:13, Pedro Venâncio wrote:
> Hi all,
>
> I have an update to the parameters that are in Datum Transformation for mainland Portugal.
>
> After an analysis of the parameters that are currently inserted in srs.db, I think we should keep only the latest parameters that are provided by the Portuguese Surveying Authority (Directorate-General of the Territory), to avoid confusion among users.
>
> So, we should keep only the transformation parameters of Molodensky, Bursa-Wolf, and two grids NTv2 that are in use here in Portugal, one from the Directorate-General of the Territory, and another from the University of Porto.
>
> I already have the SQL queries with the changes that I suggest:
>
>
> delete from tbl_datum_transform
> where source_crs_code = 4207 or source_crs_code = 4274;
>
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,p2,p3,p4,p5,p6,p7,remarks,preferred,deprecated,area_of_use_code)
> values (30000,100014,4803,4326,9606,-283.088,-70.693,117.445,-1.157,0.059,-0.652,-4.058,'Parâmetros de Transformação de Bursa-Wolf do Datum Lisboa para PT-TM06-ETRS89 (Direção-Geral do Território, 2011)',0,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,p2,p3,remarks,preferred,deprecated,area_of_use_code)
> values (30001,100015,4803,4326,9603,-303.861,-60.693,103.607,'Parâmetros de Transformação de Molodensky do Datum Lisboa para PT-TM06-ETRS89 (Direção-Geral do Território, 2011)',0,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,remarks,preferred,deprecated,area_of_use_code)
> values (30002,100016,4803,4258,9615,'ptLX_e89.gsb','Grelhas no formato NTv2 para a Transformação de Coordenadas do Sistema HGDLx para o Sistema PT-TM06/ETRS89 (José Alberto Gonçalves - FCUP)',1,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,remarks,preferred,deprecated,area_of_use_code)
> values (30003,100017,4803,4258,9615,'DLX_ETRS89_geo.gsb','Grelhas no formato NTv2 para a Transformação de Coordenadas do Sistema HGDLx para o Sistema PT-TM06/ETRS89 (Direção-Geral do Território)',0,0,1294);
>
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,p2,p3,p4,p5,p6,p7,remarks,preferred,deprecated,area_of_use_code)
> values (30004,100018,4274,4326,9606,-230.994,102.591,25.199,0.633,-0.239,0.900,1.950,'Parâmetros de Transformação de Bursa-Wolf do Datum 73 para PT-TM06-ETRS89 (Direção-Geral do Território, 2011)',0,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,p2,p3,remarks,preferred,deprecated,area_of_use_code)
> values (30005,100019,4274,4326,9603,-223.150,110.132,36.711,'Parâmetros de Transformação de Molodensky do Datum 73 para PT-TM06-ETRS89 (Direção-Geral do Território, 2011)',0,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,remarks,preferred,deprecated,area_of_use_code)
> values (30006,100020,4274,4258,9615,'pt73_e89.gsb','Grelhas no formato NTv2 para a Transformação de Coordenadas do Sistema HGD73 para o Sistema PT-TM06/ETRS89 (José Alberto Gonçalves - FCUP)',1,0,1294);
>
> insert into tbl_datum_transform (epsg_nr,coord_op_code,source_crs_code, target_crs_code,coord_op_method_code,p1,remarks,preferred,deprecated,area_of_use_code)
> values (30007,100021,4274,4258,9615,'D73_ETRS89_geo.gsb','Grelhas no formato NTv2 para a Transformação de Coordenadas do Sistema HGD73 para o Sistema PT-TM06/ETRS89 (Direção-Geral do Território)',0,0,1294);
>
>
> Regarding the queries above, there are some codes (epsg_nr, coord_op_code) that I assigned with a sequential number, because I did not know what I should put. In coord_op_method_code, I put what seemed right to me, but please confirm.
>
>
>
> Regarding NTv2 grids (http://goo.gl/jDhxJB) I have another doubt here. On Linux, these files are placed in /usr/share/proj. On Windows, using the OSGeo4W installer, they are placed in ..\OSGeo4W64\share\proj. With QGIS standalone, they are placed at ..\Program Files\QGIS Valmiera\share\proj.
> There is no possibility of copy the grid files, automatically during the installation? This will make it easier for less experienced users.
>
>
>
> However I came across something quite odd. In the Datum Transformation window, automatically arise some strange transformations (red in the imagehttp://goo.gl/iIWOuw). These transformations give huge errors, and I do not understand what they represent.
>
> May it be a bug?
>
> The transformation operation in question (epsg_nr 1571) uses as source_crs_code the 4258 (Geodetic CRS ETRS89), which is used in some target_crs_code transformations for Portugal. May it be an incorrect match between source and target codes? It is because this transformation, and these parameters, makes no sense to me.
>
> Thank you very much!
>
> Best regards,
> Pedro
>
>
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> Qgis-developer at lists.osgeo.org
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-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch  http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee

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