coordinate systempostgis
How do I convert a WGS84 lat lon point in PostGIS to Guass Kruger 3 (31467)?
Somehow, I do not seem to get it right. I tried the usual way for converting projections:
st_transform(st_setsrid(st_makepoint(50, 8), 2346), 31467)
However, this gives an out of bounds error. I assume PostGIS expects the values to be Cartesian coordinates.
1) Plugins > Manage Plugins. Enable GdalTools
2) Then:
3) Enter the source and destination SRS and the other parameters. That's it.
Typically, NAD83 and WGS84 are within one meter of each other. Your concerns about differences of 2.5 feet, which are less than a meter, indicate you do need to perform this datum transformation.
Briefly, this calculation requires knowledge of when the coordinates were collected so that their movement over time can be accounted for (primarily due to the movements of underlying tectonic plates and partly due to "episodic motion associated with earthquakes"). You first convert the raw data to equivalent coordinates referenced to specific standard dates, such as 1997.0 or 2002.0. Then you look up 14 parameters describing (a) the offset, rotation, and rescaling (i.e., a seven-parameter transformation) needed to change datums at a given date together with (b) the first derivatives of those parameters with respect to time. Multiplying (b) by the elapsed time and adding to (a) gives a first-order approximation to the needed seven-parameter transformation, which you then apply.
Although the procedure is not mathematically difficult, it is rather involved and contingent on details of how your data were originally collected and processed. An NOAA paper, Transformations Between NAD83 and WGS84, provides a clear, readable explanation. It recommends you use interactive "Horizontal Time-Dependent Position" software, HTDP, available on the NOAA Website at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml. The Fortran source code consists primarily of the coefficients of the plate tectonic model plus some interface code, but I estimate around 3,000 lines actually do calculations. It could be a significant pain to port.
Best Answer
Maybe just a typo? WGS84 is 4326.