I have the following problem: I want to convert from WGS84 to "Anguilla 1957 / British West Indies Grid" (EPSG 2000). This seems to be straight-forward, as the transformation is a simple Transverse Mercator and the projection uses the Clarke 1880 Ellipsoid without any datum shift. My result differs significantly (some 400m) from the one i.e. epsg.io is returning.
The reason seems to be the datum transformation chain. Since the code is implemented such that it can convert from any cs to any cs, it also in this case does
- WGS84 geographic -> WGS84 Geocentric (using the WGS ellipsoid)
- WGS84 Geocentric -> Clarke 1880 Geocentric (nothing to do here)
- Clarke 1880 Geocentric -> Clarke 1880 Geographic (now using the Clarke Ellipsoid)
The last step is giving me a headache now, because the output of step 3 is not equal to the input at step 1, while the same conversion returns the exact input on reference pages I've checked.
Should and can a "Geographic Ellipsoid 1->Geocentric->Geographic Ellipsoid 2" Conversion change latitude and/or longitude?
Here's the steps I take: I basically want to convert from WGS84 to Anguilla, British West Indies Grid (EPSG 2000). According to http://epsg.io/2000 this uses Datum 4600. This datum consists of the Clarke 1880 RGS ellipsoid 7012 and no datum transformation.
I'm only considering the conversion from WGS84 to Datum 4600 here, because the rest is not relevant here.
-63.000000000000014, 18.001851635270203, -78.860902368091047, which is the exact same result as mkennedy below using a 0 0 0 transformation. However, If I input the same coordinates at http://epsg.io/4600/map, The output is precisely
-63, 18. That's where the confusion comes from. May I assume that the web site is wrong and whatever coordinate system library they're using is incorrectly assuming that a conversion whose datum parameters are 0 can be skipped altogether?