[OSRS-PROJ] Re: Quick 'how-to' to on PROJ.4

[Petri J. Riipinen]

Precedence: bulk
Reply-To: osrs-proj at remotesensing.org

Hello,

Hmm... I might be out of my league now, but do you think that the 
inaccuracy might come from the datum shift? I just learned that there are 
3- and 7-parameter shifts. Should a 7-parameter shift be used for a better 
accuracy?

At least in this page: 
http://www.kms.dk/research/geodesy/reference/cotrans1_en.html there seems 
to be 7 parameters for WGS84 - ED50 - transformation. Would this help?

On this page: http://www.nls.fi/kartta/julkaisu/kkj.html there is some 
(IMO) simple transformation formula. Do you think that this formula would 
give me good enough results, if I can't get PROJ.4 to be accurate enough? 
At the end of the page there is some example that might be a good reference 
point when trying the transformations with cs2cs.

Regards,
- Petri

At 17:32 27.7.2001 , Frank Warmerdam wrote:
>"Petri J. Riipinen" wrote:
> > Ok, I almost managed to do it, except that fl_transform returns an error
> > code (100)
> >
> > First I want to mention that I found the Finnish KKJ-definitions in the
> > epsg-file and they are below:
> > # KKJ / Finland zone 1
> > <2391> +proj=tmerc +lat_0=0.000000000 +lon_0=21.000000000 +k=1.000000
> > +x_0=1500000.000 +y_0=0.000 +ellps=intl +units=m  no_defs <>
> > # KKJ / Finland zone 2
> > <2392> +proj=tmerc +lat_0=0.000000000 +lon_0=24.000000000 +k=1.000000
> > +x_0=2500000.000 +y_0=0.000 +ellps=intl +units=m  no_defs <>
> > # KKJ / Finland Uniform Coordinate System
> > <2393> +proj=tmerc +lat_0=0.000000000 +lon_0=27.000000000 +k=1.000000
> > +x_0=3500000.000 +y_0=0.000 +ellps=intl +units=m  no_defs <>
> > # KKJ / Finland zone 4
> > <2394> +proj=tmerc +lat_0=0.000000000 +lon_0=30.000000000 +k=1.000000
> > +x_0=4500000.000 +y_0=0.000 +ellps=intl +units=m  no_defs <>
> >
> > I'm guessing that the Uniform Coordinate System is the one that I should
> > use with Shapefiles and then different zones with different "vertical
> > stripes" of Finland, when dealing with raster images.
>...
> > GPS-measurements:
> > 1        6010.570       2455.930      GPS: FINLANDIA-HOUSE
> > 2        6012.467       2456.127      GPS: RAILWAY YARD
> > 3        6013.045       2458.826      GPS: VIIKKI MUSEUM
> >
> > Output in KKJ:
> > 1        6674205.       2551915.      GPS: FINLANDIA-HOUSE
> > 2        6677730.       2552047.      GPS: RAILWAY YARD
> > 3        6678839.       2554525.      GPS: VIIKKI MUSEUM
>
>Petri,
>
>As suggested your main problem is that these angles need to be translated
>into degrees minutse and seconds (or decimal degrees) rather than the odd
>DDMM.mm format.
>
>Given that I tried a few experiments and still wasn't able to get very close
>results.  The uniform coordinate system gave results that were way off, but
>zone 2 gave me this (once without datum shift, once with).
>
>warmerda at gdal[139]% cs2cs +proj=tmerc +lat_0=0 +lon_0=24 +k=1.0 
>+x_0=2500000.0 +y_0=0.0 +ellps=intl +units=m +towgs84=-87,-98,-121 +to 
>+proj=latlong +ellps=intl
>2551915 6674205
>24d56'7.162"E   60d10'33.578"N 0.005
>warmerda at gdal[140]% cs2cs +proj=tmerc +lat_0=0 +lon_0=24 +k=1.0 
>+x_0=2500000.0 +y_0=0.0 +ellps=intl +units=m +towgs84=-87,-98,-121 +to 
>+proj=latlong
>+datum=WGS84
>2551915 6674205
>24d56'3.778"E   60d10'32.451"N 17.536
>
>However, this is still something like 15 seconds off in the easting which is
>pretty dramatic.
>
>I am not sure what to do next to get proper results.
>
>Best regards,
>
>---------------------------------------+--------------------------------------
>I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush    | Geospatial Programmer for Rent

<><><><><><><><>
   Petri J. Riipinen
petri.riipinen at nic.fi
<><><><><><><><>
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