Ulises Ibarra via PROJ <proj@lists.osgeo.org> writes: > * I need to specify in detail because I think I have no idea what I'm doing > :P.
> * So I understand that the k is not necessary to use in the command. Is > this correct? Javier said you had the wrong value. UTM is a particular instance of TM. Besides a defined central meridian scale factor, there are 60 zones each with their central meridian. So try it with no +k at all. > * I don't understand what you said about there being people who use both > NAD83 and WGS84 and I am using ITRF2008, could you explain it better? > Maybe I shouldn't specify the ellipsoid? I guessed from the zone that you are in North America; maybe that was wrong. Each datum has an associated ellipsoid. Many (large majority?) use GRS80. WGS84, used in GPS and by the US DoD, but not really of interest for precise positioning, uses an ellipsoid which is almost GRS80, arguably because of rounding and a different approach to specifying it. But it is simply different. The effect of this is tiny; my memory is that it's about 1 mm at the earth's surface for coordinates. When you ask proj to transform from some projected coordinate system like UTM to geodetic (lat/lon) coordinates, you need to specify an ellipsoid. Unless the coordinates are in a CRS which specifies both UTM and a base datum, in which case it's implicit. But you have data in ITRF2008, and you aren't telling proj that. You are just doing projections. That's totally ok -- that's how proj used to be. But you need to be aware of the datum and ellipsoid yourself. I think you are getting it right. _______________________________________________ PROJ mailing list PROJ@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/proj
