[Proj] TM06 for Portugal

[Roger Oberholtzer]

On Mon, 2010-06-07 at 10:18 +0100, Jose Gonçalves wrote:
> Roger
> 
> The test data cannot be correct. ETRS89 coincides with WGS84 (or
> better ITRF) in 1989 and the current discplacement is only a few
> decimeters. The lat-long differences between your coordinates are
> 0.080" and 0.122", which correspond to approximately 2.9 m in lat and
> 2.5 m in long, i. e the differences you get in the projected
> coordinates.
> 
> Yout test point belongs to the portuguese geodetic network. The ETRS89
> coordinates are correct, as you can check in:
> 
> http://www.igeo.pt/produtos/geodesia/vg/rgn/ficha.asp?num=873
> (open with Internet Explorer)
> 
> Where did you get the WGS84 coordinates? They must be wrong.

>From Estradas de Portugal. I agree about the ETRS89 being correct
(meaning that given the proj transformation I described, the expected
northing/easting values are derived). I was surprised when they provided
two sets of lat/long values. They explained them by saying that the two
sets of LAT/LONG describe the same physical location, one in WGS84 and
the other in ETRS89. I have to trust that they have not mislabeled the
data. Especially after I asked for a confirmation.

What I am trying to accomplish is transforming WGS84 LAT/LONG from a GPS
receiver to both TM06 and MPG73 northings/eastings. I have started with
TM06. I will not have any ETRS89 lat/long values. The only reason they
might exist would be if proj makes them internally as a step in
converting the source WGS84 lat/longs into the desired TM06
northing/eastings.

How would you convert WGS84 lat/long into TM06 northing/easting? I know
that WGS84 is so close to ETR89 here that one 'could' use the WGS84
values in the transform from ETRS89 to TM06. But how would I do it the
'proper' way with proj?

> 
> Regards
> 
> José A. Gonçalves
> Univ. of Porto, Portugal
> 
> 
> 
> 2010/6/7 Roger Oberholtzer <roger at opq.se>
>         On Thu, 2010-02-18 at 16:40 +0100, Roger Oberholtzer wrote:
>         
>         I now have some test data for the conversion from WGS84
>         lat/long to TM06
>         northing/eastings. The suggested proj conversion of:
>         
>              "+proj=tmerc "
>              "+ellps=GRS80 "
>              "+k=1.0 "
>              "+x_0=0 "
>              "+y_0=0 "
>              "+lon_0=-8.133108333333334 "
>              "+lat_0=39.66825833333333 "
>              "+towgs84=0,0,0,0,0,0,0 "
>         
>         seems in fact to work with ETRS89 lat/long, not WGS84
>         lat/long. When
>         provided with WGS84 lat/long, the resulting northings/eastings
>         are a few
>         meters away. (Assuming my test data from the Portuguese Road
>         Department
>         is correct. I have double checked, so it might very well be.)
>          In fact,
>         it is a small error, but I want to provide the best I can. I
>         am guessing
>         that I need to change my +towgs84= to cause the WGS84
>         lat/longs to be
>         converted to ETRS89. Does anyone know the proper values?
>         
>         This begs the question: what does
>         http://spatialreference.org/ref/epsg/3763/ assume is the datum
>         of the
>         original lat/longs? Seems it assumes ETRS89, not WGS84.
>         
>         Here is a sample location that I have been provided (all
>         altitudes set
>         to 0.0):
>         
>          Ref (WGS84):    Latitude:   41.6743830556 Longitude:
>         -8.3312663889
>         Ref (ETRS98):    Latitude:   41.6744052222 Longitude:
>         -8.3312324722
>          Ref (TM06):    Easting:    -16498.151 Northing:
>         222796.720
>         
>         The proj conversion above properly converts the ETRS98
>         locations to
>         TM06. But I want to convert the WGS84 locations to TM06. When
>         I try
>         that, I get:
>         
>          Easting: -16500.981 Northing: 222794.265
>         
>         which is 3.747 meters away.
>         
>         --
>         Roger Oberholtzer
>         
>         OPQ Systems / Ramböll RST
>         
>         Ramböll Sverige AB
>         Krukmakargatan 21
>         P.O. Box 17009
>         SE-104 62 Stockholm, Sweden
>         
>         Office: Int +46 10-615 60 20
>         Mobile: Int +46 70-815 1696
>         
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-- 
Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696