[Proj] Datum-Shift WGS84 to Arc1960 not working propberly

[Micha Neubauer]

Hello Oscar,

thank you very much for your help! Now it works and knowing these parameters I 
can also transform my raster data with GDAL... thanks!

Indeed, I get the best fit with the parameters (dx = 160; dy = 8; dz = 300) you 
mention, that is listed by "Some manuals of GPS related products".
What are those manuals and where did you get them from. Because using the 
parameters listed on the nga homepage give fairly good results, but not quite 
the same. So just for the future, I would like to know where else to look for, 
when something is no quite matching.

Have a nice Sunday evening!
bye
micha


On Sunday, 9. August 2009, 14:14:52 OvV_HN wrote:
> ----- Original Message -----
> From: "Micha Neubauer" <Micha.Neubauer at yahoo.de>
> To: <proj at lists.maptools.org>
> Sent: Sunday, August 09, 2009 12:19 AM
> Subject: [Proj] Datum-Shift WGS84 to Arc1960 not working propberly
>
> > Dear List,
> >
> > I am in Tanzania and I want to transform some location data which I was
> > given
> > in WGS84 to the locally used Arc1960 Datum.
> >
> > So I do:
> > $ cs2cs +proj=utm +zone=37 +south +ellps=WGS84 +datum=WGS84 +units=m
> > +no_defs
> > +to +proj=utm +zone=37 +south +ellps=clrk80 +units=m +no_defs
> >
> > But it is giving me a different result than my colleague gets using the
> > garmin
> > software and I think his results are correct and mine aren't
> >
> > For the UTM WGS84 Point:
> > 332368 9613672
> >
> > Using the above command I get for UTM / Arc1960:
> > 332365.02   9613707.55 0.00
> >
> > And Garmin (which is probably correct) gives for UTM / Arc1960:
> > 332274 9613972
>
> Most importantly: add datum transformation parameters in a towgs84 string.
> How? Please read the manual.
> I merely analyzed the procedure and the parameters.
> In detail, the procedure I followed was:
>
> * Convert wgs84 coordinates x,y to lat,lon for UTM zone 37 South.
> * Molodensky transform to Arc 1960 Tanzania datum.
> The transformation parameters can be found on the NGA website:
> <http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryAfricaTable.ht
>ml> Note that the NGA values are from local datum to wgs84, so negate the
> values for the opposite direction.
> The negated NGA values are:
> dx = 175; dy = 23; dz = 303;
> * Convert transformed lat,lon to UTM x,y on Clarke 1880 ellipsoid, zone 37
> South.
> This gives:
> x = 332276.33; y = 9613976.60; (meters)
> I used the Abridged Molodensky transform, a procedure likely to be used in
> a GPS device.
> Using PROJ software can give a difference of a couple of centimeters.
>
> Some manuals of GPS related products list a datum transform parameter set
> of:
> dx = 160; dy = 8; dz = 300;
> This gives:
> x = 332273.56; y = 9613972.32;
>
> The Garmin values you mentioned: 332274 9613972
>
> Oscar van Vlijmen
>
>
>
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