Data types¶
This section describes the numerous data types in use in PROJ.4. As a rule
of thumb PROJ.4 data types are prefixed with PJ_
, or in one particular case,
is simply called PJ
. A few notable exceptions can be traced
back to the very early days of PROJ.4 when the PJ_
prefix was not
consistently used.
Transformation objects¶
-
PJ
¶ Object containing everything related to a given projection or transformation. As a user of the PROJ.4 library you are only exposed to pointers to this object and the contents is hidden behind the public API.
PJ
objects are created withproj_create()
and destroyed withproj_destroy()
.
-
PJ_DIRECTION
¶ Enumeration that is used to convey in which direction a given transformation should be performed. Used in transformation function call as described in the section on transformation functions.
Forward transformations are defined with the :c:
typedef enum proj_direction { PJ_FWD = 1, /* Forward */ PJ_IDENT = 0, /* Do nothing */ PJ_INV = -1 /* Inverse */ } PJ_DIRECTION;
-
PJ_FWD
¶ Perform transformation in the forward direction.
-
PJ_IDENT
¶ Identity. Do nothing.
-
PJ_INV
¶ Perform transformation in the inverse direction.
-
-
PJ_CONTEXT
¶ Context objects enable safe multi-threaded usage of PROJ.4. Each
PJ
object is connected to a context (if not specified, the default context is used). All operations within a context should be performed in the same thread.PJ_CONTEXT
objects are created withproj_context_create()
and destroyed withproj_context_destroy()
.
-
PJ_AREA
¶ Opaque object describing an area in which a transformation is performed.
Note
This object is not fully implemented yet. It is to be used with
proj_create_crs_to_crs()
to select the best transformation between the two input coordinate reference systems.
2 dimensional coordinates¶
Various 2-dimensional coordinate data types.
-
PJ_LP
¶ Geodetic coordinate, latitude and longitude. Usually in radians.
typedef struct { double lam, phi; } PJ_LP;
-
double
PJ_LP.lam
¶ Longitude. Lambda.
-
double
PJ_LP.phi
¶ Latitude. Phi.
-
double
3 dimensional coordinates¶
The following data types are the 3-dimensional equivalents to the data types above.
-
PJ_LPZ
¶ 3-dimensional version of
PJ_LP
. Holds longitude, latitude and a vertical component.typedef struct { double lam, phi, z; } PJ_LPZ;
-
double
PJ_LPZ.lam
¶ Longitude. Lambda.
-
double
PJ_LPZ.phi
¶ Latitude. Phi.
-
double
PJ_LPZ.z
¶ Vertical component.
-
double
-
PJ_XYZ
¶ Cartesian coordinate in 3 dimensions. Extension of
PJ_XY
.typedef struct { double x, y, z; } PJ_XYZ;
-
double
PJ_XYZ.x
¶ Easting or the X component of a 3D cartesian system.
-
double
PJ_XYZ.y
¶ Northing or the Y component of a 3D cartesian system.
-
double
PJ_XYZ.z
¶ Vertical component or the Z component of a 3D cartesian system.
-
double
Spatiotemporal coordinate types¶
The following data types are extensions of the triplets above into the time domain.
-
PJ_LPZT
¶ Spatiotemporal version of
PJ_LPZ
.typedef struct { double lam; double phi; double z; double t; } PJ_LPZT;
-
double
PJ_LPZT.lam
¶ Longitude.
-
double
PJ_LPZT.phi
¶ Latitude
-
double
PJ_LPZT.z
¶ Vertical component.
-
double
PJ_LPZT.t
¶ Time component.
-
double
-
PJ_XYZT
¶ Generic spatiotemporal coordinate. Useful for e.g. cartesian coordinates with an attached time-stamp.
typedef struct { double x; double y; double z; double t; } PJ_XYZT;
-
double
PJ_XYZT.x
¶ Easting or the X component of a 3D cartesian system.
-
double
PJ_XYZT.y
¶ Northing or the Y component of a 3D cartesian system.
-
double
PJ_XYZT.z
¶ Vertical or the Z component of a 3D cartesian system.
-
double
PJ_XYZT.t
¶ Time component.
-
double
Ancillary types for geodetic computations¶
Complex coordinate types¶
-
PJ_COORD
¶ General purpose coordinate union type, applicable in two, three and four dimensions. This is the default coordinate datatype used in PROJ.
typedef union { double v[4]; PJ_XYZT xyzt; PJ_UVWT uvwt; PJ_LPZT lpzt; PJ_XYZ xyz; PJ_UVW uvw; PJ_LPZ lpz; PJ_XY xy; PJ_UV uv; PJ_LP lp; } PJ_COORD ;
-
double v[4]
Generic four-dimensional vector.
-
Projection derivatives¶
-
PJ_FACTORS
¶ Various cartographic properties, such as scale factors, angular distortion and meridian convergence. Calculated with
proj_factors()
.typedef struct { double meridional_scale; double parallel_scale; double areal_scale; double angular_distortion; double meridian_parallel_angle; double meridian_convergence; double tissot_semimajor; double tissot_semiminor; double dx_dlam; double dx_dphi; double dy_dlam; double dy_dphi; } PJ_FACTORS;
-
double
PJ_FACTORS.meridional_scale
¶ Meridional scale at coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.parallel_scale
¶ Parallel scale at coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.areal_scale
¶ Areal scale factor at coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.angular_distortion
¶ Angular distortion at coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.meridian_parallel_angle
¶ Meridian/parallel angle, \(\theta^\prime\), at coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.meridian_convergence
¶ Meridian convergence at coordinate \(\left(\lambda,\phi\right)\). Sometimes also described as grid declination.
-
double
-
double
PJ_FACTORS.tissot_semimajor
¶ Maximum scale factor.
-
double
PJ_FACTORS.tissot_semiminor
¶ Minimum scale factor.
-
double
PJ_FACTORS.dx_dlam
¶ Partial derivative \(\frac{\partial x}{\partial \lambda}\) of coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.dy_dlam
¶ Partial derivative \(\frac{\partial y}{\partial \lambda}\) of coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.dx_dphi
¶ Partial derivative \(\frac{\partial x}{\partial \phi}\) of coordinate \(\left(\lambda,\phi\right)\).
-
double
PJ_FACTORS.dy_dphi
¶ Partial derivative \(\frac{\partial y}{\partial \phi}\) of coordinate \(\left(\lambda,\phi\right)\).
-
double
List structures¶
-
PJ_OPERATIONS
¶ Description a PROJ.4 operation
struct PJ_OPERATIONS { char *id; /* operation keyword */ PJ *(*proj)(PJ *); /* operation entry point */ char * const *descr; /* description text */ };
-
char *
id
¶ Operation keyword.
-
char * const *
Description of operation.
-
char *
-
PJ_ELLPS
¶ Description of ellipsoids defined in PROJ.4
struct PJ_ELLPS { char *id; char *major; char *ell; char *name; };
-
char *
id
¶ Keyword name of the ellipsoid.
-
char *
major
¶ Semi-major axis of the ellipsoid, or radius in case of a sphere.
-
char *
ell
¶ Elliptical parameter, e.g. rf=298.257 or b=6356772.2.
-
char *
name
¶ Name of the ellipsoid
-
char *
-
PJ_UNITS
¶ Distance units defined in PROJ.
struct PJ_UNITS { char *id; /* units keyword */ char *to_meter; /* multiply by value to get meters */ char *name; /* comments */ double factor; /* to_meter factor in actual numbers */ };
-
char *
id
¶ Keyword for the unit.
-
char *
to_meter
¶ Text representation of the factor that converts a given unit to meters
-
char *
name
¶ Name of the unit.
-
double
factor
¶ Conversion factor that converts the unit to meters.
-
char *
Info structures¶
-
PJ_INFO
¶ Struct holding information about the current instance of PROJ. Struct is populated by
proj_info()
.typedef struct { int major; int minor; int patch; const char *release; const char *version; const char *searchpath; } PJ_INFO;
-
const char *
PJ_INFO.release
¶ Release info. Version number and release date, e.g. “Rel. 4.9.3, 15 August 2016”.
-
const char *
PJ_INFO.version
¶ Text representation of the full version number, e.g. “4.9.3”.
-
int
PJ_INFO.major
¶ Major version number.
-
int
PJ_INFO.minor
¶ Minor version number.
-
int
PJ_INFO.patch
¶ Patch level of release.
-
const char
PJ_INFO.searchpath
¶ Search path for PROJ. List of directories separated by semicolons (Windows) or colons (non-Windows), e.g. “C:\Users\doctorwho;C:\OSGeo4W64\share\proj”. Grids and init files are looked for in directories in the search path.
-
const char *
-
PJ_PROJ_INFO
¶ Struct holding information about a
PJ
object. Populated byproj_pj_info()
. ThePJ_PROJ_INFO
object provides a view into the internals of aPJ
, so once thePJ
is destroyed or otherwise becomes invalid, so does thePJ_PROJ_INFO
typedef struct { const char *id; const char *description; const char *definition; int has_inverse; double accuracy; } PJ_PROJ_INFO;
-
const char *
PJ_PROJ_INFO.id
¶ Short ID of the operation the
PJ
object is based on, that is, what comes afther the+proj=
in a proj-string, e.g. “merc”.
-
const char *
PJ_PROJ_INFO.description
¶ Long describes of the operation the
PJ
object is based on, e.g. “Mercator Cyl, Sph&Ell lat_ts=”.
-
const char *
PJ_PROJ_INFO.definition
¶ The proj-string that was used to create the
PJ
object with, e.g. “+proj=merc +lat_0=24 +lon_0=53 +ellps=WGS84”.
-
int
PJ_PROJ_INFO.has_inverse
¶ 1 if an inverse mapping of the defined operation exists, otherwise 0.
-
double
PJ_PROJ_INFO.accuracy
¶ Expected accuracy of the transformation. -1 if unknown.
-
const char *
-
PJ_GRID_INFO
¶ Struct holding information about a specific grid in the search path of PROJ. Populated with the function
proj_grid_info()
.typedef struct { char gridname[32]; char filename[260]; char format[8]; LP lowerleft; LP upperright; int n_lon, n_lat; double cs_lon, cs_lat; } PJ_GRID_INFO;
-
char PJ_GRID_INFO.gridname[32]
Name of grid, e.g. “BETA2007.gsb”.
-
char
PJ_GRID_INFO
¶ Full path of grid file, e.g. “C:\OSGeo4W64\share\proj\BETA2007.gsb”
-
char PJ_GRID_INFO.format[8]
File format of grid file, e.g. “ntv2”
-
LP
PJ_GRID_INFO.lowerleft
¶ Geodetic coordinate of lower left corner of grid.
-
LP
PJ_GRID_INFO.upperright
¶ Geodetic coordinate of upper right corner of grid.
-
int
PJ_GRID_INFO.n_lon
¶ Number of grid cells in the longitudinal direction.
-
int
PJ_GRID_INFO.n_lat
¶ Number of grid cells in the latitudianl direction.
-
double
PJ_GRID_INFO.cs_lon
¶ Cell size in the longitudinal direction. In radians.
-
double
PJ_GRID_INFO.cs_lat
¶ Cell size in the latitudinal direction. In radians.
-
-
PJ_INIT_INFO
¶ Struct holding information about a specific init file in the search path of PROJ. Populated with the function
proj_init_info()
.typedef struct { char name[32]; char filename[260]; char version[32]; char origin[32]; char lastupdate[16]; } PJ_INIT_INFO;
-
char PJ_INIT_INFO.name[32]
Name of init file, e.g. “epsg”.
-
char PJ_INIT_INFO.filename[260]
Full path of init file, e.g. “C:\OSGeo4W64\share\proj\epsg”
-
char PJ_INIT_INFO.version[32]
Version number of init-file, e.g. “9.0.0”
-
char PJ_INIT_INFO.origin[32]
Originating entity of the init file, e.g. “EPSG”
-
char
PJ_INIT_INFO.lastupdate
¶ Date of last update of the init-file.
-
Logging¶
-
PJ_LOG_LEVEL
¶ Enum of logging levels in PROJ. Used to set the logging level in PROJ. Usually using
proj_log_level()
.-
PJ_LOG_NONE
¶ Don’t log anything.
-
PJ_LOG_ERROR
¶ Log only errors.
-
PJ_LOG_DEBUG
¶ Log errors and additional debug information.
-
PJ_LOG_TRACE
¶ Highest logging level. Log everything including very detailed debug information.
-
PJ_LOG_TELL
¶ Special logging level that when used in
proj_log_level()
will return the current logging level set in PROJ.
New in version 5.1.0.
-
-
PJ_LOG_FUNC
¶ Function prototype for the logging function used by PROJ. Defined as
typedef void (*PJ_LOG_FUNCTION)(void *, int, const char *);
where the
void
pointer references a data structure used by the calling application, theint
is used to set the logging level and theconst char
pointer is the string that will be logged by the function.New in version 5.1.0.