The foundation of PROJ is the large number of projections available in the library. This section is devoted to the generic parameters that can be used on any projection in the PROJ library.
Below is a list of PROJ parameters which can be applied to most coordinate system definitions. This table does not attempt to describe the parameters particular to particular projection types. These can be found on the pages documenting the individual projections.
Semimajor radius of the ellipsoid axis
Semiminor radius of the ellipsoid axis
Ellipsoid name (see
Scaling factor (deprecated)
Latitude of origin
Center longitude to use for wrapping (see below)
Allow longitude output outside -180 to 180 range, disables wrapping (see below)
Alternate prime meridian (typically a city name, see below)
Projection name (see
meters, US survey feet, etc.
In the sections below most of the parameters are explained in details.
Horizontal units can be specified using the
+units keyword with a symbolic
name for a unit (i.e.
us-ft). Alternatively the translation to meters can be
specified with the
+to_meter keyword (i.e. 0.304800609601219 for US feet). The
-lu argument to cs2cs or proj can be used to list
symbolic unit names. The default unit for projected coordinates is the meter.
A few special projections deviate from this behavior, most notably the
latlong pseudo-projection that returns degrees.
Vertical (Z) units can be specified using the
+vunits keyword with a
symbolic name for a unit (i.e.
us-ft). Alternatively the translation to
meters can be specified with the
+vto_meter keyword (i.e. 0.304800609601219
for US feet). The
-lu argument to cs2cs or proj can
be used to list symbolic unit names. If no vertical units are specified, the
vertical units will default to be the same as the horizontal coordinates.
proj does not handle vertical units at all and hence the
+vto_meter argument will be ignored.
Scaling of output units can be done by applying the
+k_0 argument. The
returned coordinates are scaled by the value assigned with the
Input units for parameters that can be understood to be either decimal degrees or radians are interpreted to be decimal degrees by convention.
Explicit specification of input units can be accomplished by adding the appropriate suffix to input values.
Example of use. The longitude of the central meridian
+lon_0=90, can also be expressed more explicitly
with units of decimal degrees as
+lon_0=90d or in radian
Virtually all coordinate systems allow for the presence of a false easting
+x_0) and northing (
+y_0). Note that these values are always expressed in
meters even if the coordinate system is some other units. Some coordinate
systems (such as UTM) have implicit false easting and northing values.
By default PROJ wraps output longitudes in the range -180 to 180. The
switch can be used to disable the default wrapping which is done at a low level
pj_inv(). This is particularly useful with projections like the
Equidistant Cylindrical (Plate Carrée) or Mercator
where it could be desirable for X values past -20000000 (roughly) to continue
past -180 instead of wrapping to +180.
Note however that for most projections where the 180 meridian does not project
to a straight line,
+over will have no effect or will not lead to expected
+lon_wrap option can be used to provide an alternative means of doing
longitude wrapping within
pj_transform(). The argument to this option is a
center longitude. So
+lon_wrap=180 means wrap longitudes in the range 0 to
360. Note that
+over does not disable
A prime meridian may be declared indicating the offset between the prime meridian of the declared coordinate system and that of greenwich. A prime meridian is declared using the "pm" parameter, and may be assigned a symbolic name, or the longitude of the alternative prime meridian relative to greenwich.
Currently prime meridian declarations are only utilized by the
pj_transform() API call, not the
Consequently the user utility cs2cs does honour prime meridians but
the proj user utility ignores them.
The following predeclared prime meridian names are supported. These can be
listed using with
Example of use. The location
lat=0 in the greenwich based lat/long
coordinates is translated to lat/long coordinates with Madrid as the prime
cs2cs +proj=latlong +datum=WGS84 +to +proj=latlong +datum=WGS84 +pm=madrid 0 0 3d41'16.48"E 0dN 0.000
Starting in PROJ 4.8.0, the +axis argument can be used to control the axis orientation of the coordinate system. The default orientation is "easting, northing, up" but directions can be flipped, or axes flipped using combinations of the axes in the +axis switch. The values are:
"e" - Easting
"w" - Westing
"n" - Northing
"s" - Southing
"u" - Up
"d" - Down
They can be combined in +axis in forms like:
+axis=enu- the default easting, northing, elevation.
+axis=neu- northing, easting, up - useful for "lat/long" geographic coordinates, or south orientated transverse mercator.
+axis=wnu- westing, northing, up - some planetary coordinate systems have "west positive" coordinate systems
+axis argument does not work with the proj command line