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 (always in meters)
Semiminor radius of the ellipsoid axis (always in meters)
Ellipsoid name (see
Scaling factor (deprecated)
Latitude of origin (in degree if no angular unit specified)
Central meridian (in degree if no angular unit specified)
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
Horizontal coordinate system units (meters, US survey feet, etc.)
Vertical coordinate system units.
False easting (always in meters)
False northing (always in meters)
In the sections below most of the parameters are explained in details.
Horizontal coordinate system units can be specified using the
with a symbolic me for a unit (i.e.
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.
Note that this does not affect the units of linear parameters such as
+b which should always be specified in meters.
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 (unitless).
The returned coordinates are scaled by the value assigned with the
parameter. This parameter is only used by projections that mention using it,
and its exact effect is projection dependent.
Input units for angular parameters (
+pm, etc.) are
interpreted to be decimal degrees by convention.
Explicit specification of input angular units can be accomplished by adding the
appropriate suffix to input values.
The sign of an angle is taken from either a
or the last character specifying a cardinal direction,
E (East) or
N (North) are positive
W (West) or
S (South) are negative.
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
Angles can be expressed in DMS notation, using
' after arcminutes
" after arcseconds, ending with optional cardinal direction.
+pm=3d41\'14.55\"W may be required.
Degree-minute notation does not require any quotation symbols.
All of these are equivalent values:
+pm=17d40'W (escaped as
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. It has only effect with operations that output angular
coordinates, such as
+proj=longlat The argument to this option is a
center longitude. So
+lon_wrap=180 means wrap longitudes in the range 0 to
$ echo -1 0 cs2cs +proj=longlat +to +proj=longlat +lon_wrap=180
359dE 0dN 0.000
+over does not disable
A prime meridian may be declared indicating the longitude 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
an angle in DMS or decimal degrees format, or as a hard-coded name.
Hard-coded prime meridians can be listed with
Note that the following list is no longer updated, and some values
may conflict with other sources.
Example of use. The location
lat=0 in the greenwich based lat/long
coordinates is translated to lat/long coordinates with Lisbon as the prime
cs2cs +proj=latlong +datum=WGS84 +to +proj=latlong +datum=WGS84 +pm=lisbon
9d7'54.862"E 0dN 0.000
Decimal degrees can also be simply specified for the prime meridian.
echo 13d30E 45N | proj +proj=merc +pm=13.5
See Units for other examples of angular inputs.
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
Order of applications of parameters¶
In the forward direction (from geodetic to projected coordinates), steps are performed in the following order:
subtracting prime meridian (
+pm) to input coordinate longitude
subtracting central meridian (
+lon_0) to input coordinate longitude
normalizing input coordinate longitude to [-180, 180], unless
application of map projection formula on a spheroid of radius 1 and with the eccentricity of the target spheroid specified. Includes taking into account projection parameters such as
+lat_0, and other projection specific parameters
scaling of output x, y values by the semimajor axis
addition of false easting
+x_0to x and false northing
scaling of output x, y by the output horizontal unit (
scaling of output z by the output vertical unit (
application of axis orientation and order (
This is implemented mostly in fwd.cpp
For the reverse direction (from projected coordinates to geodetic coordinates), reverse steps are performed in the reverse order.