Rectify Brazil SAD69 to WGS84 transformation parameters

proj4-bot commented 9 years ago

Reported by lpbjunior on 7 Jul 2014 19:45 UTC Dear all,

The transformation parameters values currently available between ''SAD69'' to ''WGS84'' ''DATA'' doesn't correspond to the official transformation parameters values established by the Brazilian Government institute, named '''Instituto Brasileiro de Geografia e Estatstica''' ('''IBGE''' - ''Brazilian Institute of Geography and Statistics'').

Those values are coarse approximations, a rough average, for the 3-parameters transformation between '''''SAD69 <-> WGS84''''' that would be applied for the all South American countries.

However, as a rough average it causes serious errors to the geographic data positioning mainly when using ''On-The-Fly'' GIS software functionality, as occurs in '''Quantum GIS (QGIS)'''.

== PROJ.4 SAD69 to WGS84 transformations parameters values currently available: ==

'''SAD69 - EPSG:4618'''

+proj=longlat +ellps=aust_SA +towgs84=-57,1,-41,0,0,0,0 +no_defs

+towgs84='''''-57''''','''''1''''','''''-41'''''

'''SAD69 - EPSG:4291''' (deprecated due correction of ellipsoid 1/f to 2 decimal places exactly)

+proj=longlat +ellps=GRS67 +towgs84=-57,1,-41,0,0,0,0 +no_defs

+towgs84='''''-57''''','''''1''''','''''-41'''''

'''SAD69 / Brazil Polyconic EPSG:29101'''

+proj=poly +lat_0=0 +lon_0=-54 +x_0=5000000 +y_0=10000000 +ellps=aust_SA +towgs84=-57,1,-41,0,0,0,0 +units=m +no_defs

+towgs84='''''-57''''','''''1''''','''''-41'''''

'''Brazil UTM zones coverage: 18 to 25'''

UTM zones 18S, 19S, 19N, 20S, 20N, 21S, 21N, 22S, 22N, 23S, 23N, 24S, 24N and 25S
Example: ''SAD69 / UTM zone 18S''

+proj=utm +zone=18 +south +ellps=aust_SA +towgs84=-57,1,-41,0,0,0,0 +units=m +no_defs

+towgs84='''''-57''''','''''1''''','''''-41'''''

== Brazilian official transformations parameters values and methods ==

To the Brazil territorial extension the IBGE had already established the correct and official 3-parameters transformations '''''SAD69 -> WGS84'''''. They had published four official transformation parameters and the criteria that differentiates one choice from another are the technic and the precision provided by the method used to obtain the coordinates, all resumed below:

'''## (1)'''

Coordinates obtainment based on stations established by the classical techniques of positioning ''before'' the 1996 Network Global Adjustment based on the ''Rede Clssica 1969'' '''(Classic Network)''' ''until 15/9/1996''''':

---> method: NTv2

---> parameters: file ''SAD'''69'''_003''.gsb'''

---> bounds: North: 4 30' / South: 34 10' / East: 33 30' / West: 63 30'

SAD69_003.gsb

'''## (2)'''

Coordinates obtainment based on stations established by the classical techniques of positioning ''after'' the 1996 Network Global Adjustment based on the ''Rede Clssica 1969/96'' '''(Classic Network)''' ''after 15/9/1996''''':

---> method: NTv2

---> parameters: file ''SAD'''96'''_003''.gsb'''

---> bounds: North: 5 30' / South: 34 10' / East: 33 30' / West: 63 20'

SAD96_003.gsb

'''## (3)'''

Coordinates obtained '''''between 01/1/1987 and 1/1/1994''''' and based on stations established by the spatial techniques of positioning (''Doppler stations'' or ''GPS stations'') or through ''GPS receivers'':

''Resoluo do Presidente do IBGE n 23 de 21 de fevereiro de 1989'' (IBGE's President Resolution n 23/1989 Download Link):

---> method: MOLODENSKII (Resoluo do Presidente do IBGE n 22, de 21 de julho de 1983)

---> parameters:

DX = -66,87
DY = +4,37
DZ = -38,52

To the opposite direction transformation, '''''WGS84 -> SAD69''''', just change the vector signal. Eg: DX = +66,87, DY = -4,37, DZ = +38,52. ---> bounds: North: 5 30' / South: 34 10' / East: 33 30' / West: 74 15'

'''## (4)'''

Coordinates obtained '''''after 1/1/1994''''' and based on stations established by the spatial techniques of positioning (''Doppler stations'' or ''GPS stations'') or through ''GNSS (GPS or GLONASS) receivers'':

''Resoluo do Presidente do IBGE n 01 de 25 de fevereiro de 2005'' (IBGE's President Resolution n 01/2005 Download Link):

---> method: ''Resoluo do Presidente do IBGE n 23, de 21 de janeiro de 1989, Appendant, Section 3''

---> parameters:

DX = -67,35
DY = +3,88
DZ = -38,22

To the opposite direction transformation, '''''WGS84 -> SAD69''''', just change the vector signal. Eg: DX = +67,35, DY = -3,88, DZ = +38,22. ---> bounds: North: 5 30' / South: 34 10' / East: 33 30' / West: 74 15'

Just for the records, the IBGE has grouped three of these transformations (Numbers '''1''', '''2''' and '''4''') in a software called '''''ProGriD''''', which was developed in association with the University of New Brunswick, Canada. ProGriD Explanation & Download link

Though the transformation '''Number 3''' wasn't inserted at the ProGriD software, the IBGE still suggests their use to GPS observations realized between 01/1/1987 and 01/1/1994 IBGE FAQ, Question #15
- There are no transformation parameters between WGS84 and SIRGAS2000 due to growing similarity in both ''WGS84'' and ''ITRFyy'' (used by SIRGAS2000) realizations.

== Rectification Proposals ==

So, as describe above, the rectification suggestions for those ''Proj.4 SAD69 to WGS84 3-parameteres transformations'' would be:

'''SAD69 BRAZIL 1989 - EPSG:XXXX'''

+proj=longlat +ellps=aust_SA +towgs84=-66.87,4.37,-38.52,0,0,0,0 +no_defs

+towgs84='''''-66.87''''','''''4.37''''','''''-38.52'''''

'''SAD69 BRAZIL 2005 - EPSG:XXXX'''

+proj=longlat +ellps=aust_SA +towgs84=-67.35,3.88,-38.22,0,0,0,0 +no_defs

+towgs84='''''-67.35''''','''''3.88''''','''''-38.22'''''

== Proprietary GIS softwares modifications on Brazilian CRS ==

It is also known that these modifications has started in proprietary GIS softwares, like ArcGIS, although they still not cover all cases mentioned above. There is room for a more thorough improvement. Below are the respective '''.''PRJ files''''' internal descriptions reproduced from a shapefile created in ArcGIS 10.1:

'''## SAD69'''

GEOGCS[SAD69-1996'''

GEOGCS["GCS_SAD_1969_96",DATUM["D_South_American_Datum_1969_96",SPHEROID["GRS_1967_Truncated",6378160.0,298.25]("GCS_South_American_1969",DATUM["D_South_American_1969",SPHEROID["GRS_1967_Truncated",6378160.0,298.25]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]


'''##)],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]

This kind of inaccuracy and the need to customize a Coordinate Reference System (CRS), which is a temporary and not a properly solution, cast doubt the Proj.4 based GIS softwares, if they work properly or if there are other important bugs or imprecisions that compromise the user's spatial data and, furthermore, discourages the new users adherence.

Thanks for the attention. Cheers.

lpbjunior

Migrated-From: https://trac.osgeo.org/proj/ticket/241

proj4-bot commented 9 years ago

Comment by rouault on 19 Aug 2014 10:09 UTC The current transform -57,1,-41 comes from the EPSG registry coordinate transformation n1864 : http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:coordinateOperation:EPSG::1864

The issue is that we select here since it is valid for the whole extent of SAD69, but you are only interested in Brazil, so you could use a more precise transform but that would not fit other countries where SAD69 applies.

proj4-bot commented 9 years ago

Comment by rouault on 19 Aug 2014 12:02 UTC Removing critical criticity and milestone.

proj4-bot commented 9 years ago

Comment by warmerdam on 13 Sep 2014 21:00 UTC At FOSS4G Daniel Miranda and I have gone over the Brazilian wiki page, and done several override fixes in libgeotiff (from which we derive the epsg init file). In particular, now we have values matching the desired for EPSG 4618, 4225 and 4224 and the changes should appear in libgeotiff, PROJ.4, GDAL, and PostGIS (over time). I would appreciate it if you could check how well the new proj/nad/epsg file matches you expectations and suggest remaining changes you think should be made.

kbevers commented 7 years ago

This seems to have been fixed by Frank

OSGeo / PROJ

Rectify Brazil SAD69 to WGS84 transformation parameters #241