Hi Greg The latitude at origin is defined in the EPSG https://epsg.org/coord-operation-method_9807/Transverse-Mercator.html It is used in some systems, like in Argentina (with latitude -90) and as Charles mentions in other answer, in "OSGB36 / British National Grid" (with latitude 49)
Cheers, .___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__ Entre dos pensamientos racionales hay infinitos pensamientos irracionales. On Fri, 13 Jan 2023 at 16:00, Greg Troxel <[email protected]> wrote: > Javier Jimenez Shaw <[email protected]> writes: > > > I have a question about Transverse Mercator. > > What is the impact of the parameter "Latitude of natural origin", > compared > > with the "False Northing"? (apart from the fact that one is in degrees > and > > the other in meters) > > Is there any difference on using a Latitude of natural origin of, let's > > say, 40 degrees, or compute the equivalent False Northing? > > Snyder's Album [1] says that TM uses the equator. I had never heard of > latitude of natural origin. Snyder's Manual [2] seems to align with > equator only but I may have missed it. > > It seems like there is some more complicated definition of TM. > ESRI [3] lists but does not explain latitude of natural origin. > > I would guess that latitude of natural origin means that some other > latitute is used as the place in lat/lon that maps to 0 (before adding > the false northing). But, it's an ellipsoidal projection and I can't > convince myself that this is equivalent to a different false northing. > > To me, it seems wrong or at best confusing to interchange these > parameters even if it is equivalent, as one seems to be about how the > projection is done and the other is just about moving numbers away from > 0 so they won't be negative. > > I am curious how you were led to latitude of natural origin. > > > [1] https://www.usgs.gov/publications/album-map-projections > [2] https://pubs.usgs.gov/pp/1395/report.pdf > [3] > https://desktop.arcgis.com/en/arcmap/latest/map/projections/transverse-mercator.htm >
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