[Proj] Differences in Output between proj and cs2cs
gerald.evenden at verizon.net
Tue Mar 1 15:12:52 EST 2005
If they haven't messed with "proj" and the way I programmed it, the
"datum=WGS84" parameter on the proj runline is ignored. Only the
+ellps=WGS84 has any meaning to proj. It converts the geographic
coordinates to planar coordinates based upon a spherical earth
having a radius the same as the semi-major axis of the WGS84 ellipsoid.
That is, the Equidistant Cylindrical only functions in spherical mode.
If you execute proj with the -V option, proj will list +parameters that
are not used by the projection as well as a moderately complete
diagnostic of the projected numbers.
In the case of the cs2cs program a datum change is taking place because
of the two +datum arguments. Thus the geographic coordinates are
probably changed before they get to the projection program/procedure.
On Mar 1, 2005, at 12:46 PM, Martin Thierer wrote:
> while trying to understand proj (and projections in general) I'm having
> difficulties to understand the differences I get when using the cs2cs
> to convert from Lat/Lon coordinates to Equirectangular Projection and
> same (at least: intended to be the same) conversion done with the proj
> 1. With proj:
> proj +proj=eqc +datum=WGS84 +lat_ts=48.8 +lon_0=9.48 +ellps=WGS84
> 9.48 48.8
> 0.00 5432391.15
> 2. With cs2cs:
> cs2cs -v +proj=longlat +datum=WGS84 +to +proj=eqc +datum=WGS84
> # ---- From Coordinate System ----
> #Lat/long (Geodetic)
> # +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> # ---- To Coordinate System ----
> #Equidistant Cylindrical (Plate Caree)
> # Cyl, Sph
> # lat_ts=
> # +proj=eqc +datum=WGS84 +lat_ts=48.8 +lon_0=9.48 +ellps=WGS84
> 9.48 48.8
> 0.00 5411149.43 -12062.35
> Why this difference in x the y-coordinate? And why is there a
> difference in
> the z-coordinate? As the WGS84 ellipsis is used for both source and
> shouldn't the z-coordinate in the result be 0 as well?
> Could someone please help me?
> Thank you very much!
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