Functions¶

PJ_CONTEXT* proj_context_create(void)

Returns: PJ_CONTEXT*
void proj_context_destroy(PJ_CONTEXT *ctx)

Parameters: ctx (PJ_CONTEXT*) – Threading context.

Transformation setup¶

PJ* proj_create(PJ_CONTEXT *ctx, const char *definition)

Create a transformation object from a proj-string.

Example call:

PJ *P = proj_create(0, "+proj=etmerc +lat_0=38 +lon_0=125 +ellps=bessel");


The returned PJ-pointer should be deallocated with proj_destroy().

Parameters: ctx (PJ_CONTEXT*) – Threading context. definition (const char*) – Proj-string of the desired transformation.
PJ* proj_create_argv(PJ_CONTEXT *ctx, int argc, char **argv)

Create transformation object with argc/argv-style initialization. For this application each parameter in the defining proj-string is an entry in argv.

Example call:

char *args[3] = {"proj=utm", "zone=32", "ellps=GRS80"};
PJ* P = proj_create_argv(0, 3, args);


The returned PJ-pointer should be deallocated with proj_destroy().

Parameters: ctx (PJ_CONTEXT*) – Threading context argc (int) – Count of arguments in argv argv (char**) – Vector of strings with proj-string parameters, e.g. +proj=merc PJ*
PJ* proj_create_crs_to_crs(PJ_CONTEXT *ctx, const char *srid_from, const char *srid_to, PJ_AREA *area)

Create a transformation object that is a pipeline between two known coordinate reference systems.

srid_from and srid_to should be the value part of a +init=... parameter set, i.e. “epsg:25833” or “IGNF:AMST63”. Any projection definition that can be found in a init-file in PROJ_LIB is a valid input to this function.

For now the function mimics the cs2cs app: An input and an output CRS is given and coordinates are transformed via a hub datum (WGS84). This transformation strategy is referred to as “early-binding” by the EPSG. The function can be extended to support “late-binding” transformations in the future without affecting users of the function. When the function is extended to the late-binding approach the area argument will be used. For now it is just a place-holder for a future improved implementation.

Example call:

PJ *P = proj_create_crs_to_crs(0, "epsg:25832", "epsg:25833", 0);


The returned PJ-pointer should be deallocated with proj_destroy().

Parameters: ctx (PJ_CONTEXT*) – Threading context. srid_from (const char*) – Source SRID. srid_to (const char*) – Destination SRID. area (PJ_AREA) – Descriptor of the desired area for the transformation. PJ*
PJ* proj_destroy(PJ *P)

Deallocate a PJ transformation object.

Parameters: P (PJ*) – PJ*

Coordinate transformation¶

PJ_COORD proj_trans(PJ *P, PJ_DIRECTION direction, PJ_COORD coord)

Transform a single PJ_COORD coordinate.

Parameters: P (PJ*) – direction (PJ_DIRECTION) – Transformation direction. coord (PJ_COORD) – Coordinate that will be transformed. PJ_COORD
size_t proj_trans_generic(PJ *P, PJ_DIRECTION direction, double *x, size_t sx, size_t nx, double *y, size_t sy, size_t ny, double *z, size_t sz, size_t nz, double *t, size_t st, size_t nt)

Transform a series of coordinates, where the individual coordinate dimension may be represented by an array that is either

1. fully populated
2. a null pointer and/or a length of zero, which will be treated as a fully populated array of zeroes
3. of length one, i.e. a constant, which will be treated as a fully populated array of that constant value

The strides, sx, sy, sz, st, represent the step length, in bytes, between consecutive elements of the corresponding array. This makes it possible for proj_transform() to handle transformation of a large class of application specific data structures, without necessarily understanding the data structure format, as in:

typedef struct {
double x, y;
int quality_level;
char surveyor_name[134];
} XYQS;

XYQS survey[345];
double height = 23.45;
size_t stride = sizeof (XYQS);

...

proj_trans_generic (
P, PJ_INV, sizeof(XYQS),
&(survey[0].x), stride, 345,  /*  We have 345 eastings  */
&(survey[0].y), stride, 345,  /*  ...and 345 northings. */
&height, 1,                   /*  The height is the constant  23.45 m */
0, 0                          /*  and the time is the constant 0.00 s */
);


This is similar to the inner workings of the deprecated pj_transform function, but the stride functionality has been generalized to work for any size of basic unit, not just a fixed number of doubles.

In most cases, the stride will be identical for x, y, z, and t, since they will typically be either individual arrays (stride = sizeof(double)), or strided views into an array of application specific data structures (stride = sizeof (...)).

But in order to support cases where x, y, z, and t come from heterogeneous sources, individual strides, sx, sy, sz, st, are used.

Note

Since proj_transform() does its work in place, this means that even the supposedly constants (i.e. length 1 arrays) will return from the call in altered state. Hence, remember to reinitialize between repeated calls.

Parameters: P (PJ*) – Transformation object direction – Transformation direction x (double*) – Array of x-coordinates y (double*) – Array of y-coordinates z (double*) – Array of z-coordinates t (double*) – Array of t-coordinates sx (size_t) – Step length, in bytes, between consecutive elements of the corresponding array nx (size_t) – Number of elements in the corresponding array sy (size_t) – Step length, in bytes, between consecutive elements of the corresponding array nv (size_t) – Number of elements in the corresponding array sz (size_t) – Step length, in bytes, between consecutive elements of the corresponding array nz (size_t) – Number of elements in the corresponding array st (size_t) – Step length, in bytes, between consecutive elements of the corresponding array nt (size_t) – Number of elements in the corresponding array Number of transformations successfully completed
size_t proj_trans_array(PJ *P, PJ_DIRECTION direction, size_t n, PJ_COORD *coord)

Batch transform an array of PJ_COORD.

Parameters: P (PJ*) – direction (PJ_DIRECTION) – Transformation direction n (size_t) – Number of coordinates in coord size_t 0 if all observations are transformed without error, otherwise returns error number

Error reporting¶

int proj_errno(PJ *P)

Get a reading of the current error-state of P. An non-zero error codes indicates an error either with the transformation setup or during a transformation.

Param: PJ* P: Transformation object. int
void proj_errno_set(PJ *P, int err)

Change the error-state of P to err.

param PJ* P: Transformation object. Error number.
int proj_errno_reset(PJ *P)

Clears the error number in P, and bubbles it up to the context.

Example:

void foo (PJ *P) {
int last_errno = proj_errno_reset (P);

do_something_with_P (P);

/* failure - keep latest error status */
if (proj_errno(P))
return;
/* success - restore previous error status */
proj_errno_restore (P, last_errno);
return;
}

Param: PJ* P: Transformation object. int Returns the previous value of the errno, for convenient reset/restore operations.
void proj_errno_restore(PJ *P, int err)

Reduce some mental impedance in the canonical reset/restore use case: Basically, proj_errno_restore() is a synonym for proj_errno_set(), but the use cases are very different: set indicate an error to higher level user code, restore passes previously set error indicators in case of no errors at this level.

Hence, although the inner working is identical, we provide both options, to avoid some rather confusing real world code.

See usage example under proj_errno_reset()

Parameters: P (PJ*) – Transformation object. err (int) – Error code.
const char* proj_errno_string(int err)

Get a text representation of an error number.

Parameters: err (int) – Error number. const char* String with description of error.

Note

Available from version 5.1.0.

Info functions¶

PJ_INFO proj_info(void)

Get information about the current instance of the PROJ library.

Returns: PJ_INFO
PJ_PROJ_INFO proj_pj_info(const PJ *P)

Get information about a specific transformation object, P.

Parameters: P (const PJ*) – Transformation object PJ_PROJ_INFO
PJ_GRID_INFO proj_grid_info(const char *gridname)

Get information about a specific grid.

Parameters: gridname (const char*) – Gridname in the PROJ searchpath PJ_GRID_INFO
PJ_INIT_INFO proj_init_info(const char *initname)

Get information about a specific init file.

Parameters: initname (const char*) – Init file in the PROJ searchpath PJ_INIT_INFO

Lists¶

const PJ_OPERATIONS* proj_list_operations(void)

Get a pointer to an array of all operations in PROJ. The last entry of the returned array is a NULL-entry. The array is statically allocated and does not need to be freed after use.

Print a list of all operations in PROJ:

PJ_OPERATIONS *ops;
for (ops = proj_list_operations(); ops->id; ++ops)
printf("%s\n", ops->id);

Returns: PJ_OPERATIONS*
const PJ_ELLPS* proj_list_ellps(void)

Get a pointer to an array of ellipsoids defined in PROJ. The last entry of the returned array is a NULL-entry. The array is statically allocated and does not need to be freed after use.

Returns: PJ_ELLPS*
const PJ_UNITS* proj_list_units(void)

Get a pointer to an array of distance units defined in PROJ. The last entry of the returned array is a NULL-entry. The array is statically allocated and does not need to be freed after use.

Returns: PJ_UNITS*
const PJ_PRIME_MERIDIANS* proj_list_prime_meridians(void)

Get a pointer to an array of prime meridians defined in PROJ. The last entry of the returned array is a NULL-entry. The array is statically allocated and does not need to be freed after use.

Returns: PJ_PRIME_MERIDIANS*

Distances¶

double proj_lp_dist(const PJ *P, PJ_COORD a, PJ_COORD b)

Calculate geodesic distance between two points in geodetic coordinates.

Parameters: P (PJ*) – Transformation object a (PJ_COORD) – Coordinate of first point b (PJ_COORD) – Coordinate of second point double Distance between a and b in meters.
double proj_lp_dist(const PJ *P, PJ_COORD a, PJ_COORD b)

Calculate geodesic distance between two points in geodetic coordinates.

Parameters: P (PJ*) – Transformation object a (PJ_COORD) – Coordinate of first point b (PJ_COORD) – Coordinate of second point double Distance between a and b in meters.
double proj_xy_dist(PJ_COORD a, PJ_COORD b)

Calculate 2-dimensional euclidean between two projected coordinates.

Parameters: a (PJ_COORD) – First coordinate b (PJ_COORD) – Second coordinate double Distance between a and b in meters.
double proj_xyz_dist(PJ_COORD a, PJ_COORD b)

Calculate 3-dimensional euclidean between two projected coordinates.

Parameters: a (PJ_COORD) – First coordinate b (PJ_COORD) – Second coordinate double Distance between a and b in meters.

Various¶

PJ_COORD proj_coord(double x, double y, double z, double t)

Initializer for the PJ_COORD union. The function is shorthand for the otherwise convoluted assignment. Equivalent to

PJ_COORD c = {{10.0, 20.0, 30.0, 40.0}};


or

PJ_COORD c;
// Assign using the PJ_XYZT struct in the union
c.xyzt.x = 10.0;
c.xyzt.y = 20.0;
c.xyzt.z = 30.0;
c.xyzt.t = 40.0;


Since PJ_COORD is a union of structs, the above assignment can also be expressed in terms of the other types in the union, e.g. PJ_UVWT or PJ_LPZT.

Parameters: x (double) – 1st component in a PJ_COORD y (double) – 2nd component in a PJ_COORD z (double) – 3rd component in a PJ_COORD t (double) – 4th component in a PJ_COORD PJ_COORD
double proj_roundtrip(PJ *P, PJ_DIRECTION direction, int n, PJ_COORD *coord)

Measure internal consistency of a given transformation. The function performs n round trip transformations starting in either the forward or reverse direction. Returns the euclidean distance of the starting point coo and the resulting coordinate after n iterations back and forth.

Parameters: P (const PJ*) – direction (PJ_DIRECTION) – Starting direction of transformation n (int) – Number of roundtrip transformations coord (PJ_COORD) – Input coordinate double Distance between original coordinate and the resulting coordinate after n transformation iterations.
PJ_FACTORS proj_factors(PJ *P, PJ_COORD lp)

Calculate various cartographic properties, such as scale factors, angular distortion and meridian convergence. Depending on the underlying projection values will be calculated either numerically (default) or analytically.

The function also calculates the partial derivatives of the given coordinate.

Parameters: P (const PJ*) – Transformation object lp (const PJ_COORD) – Geodetic coordinate PJ_FACTORS
double proj_torad(double angle_in_degrees)

Parameters: angle_in_degrees (double) – Degrees double Radians
double proj_todeg(double angle_in_radians)

Parameters: angle_in_radians (double) – Radians double Degrees
double proj_dmstor(const char *is, char **rs)

Convert string of degrees, minutes and seconds to radians. Works similarly to the C standard library function strtod().

Parameters: is (const char*) – Value to be converted to radians rs – Reference to an already allocated char*, whose value is set by the function to the next character in is after the numerical value.
char *proj_rtodms(char *s, double r, int pos, int neg)

Convert radians to string representation of degrees, minutes and seconds.

Parameters: s (char*) – Buffer that holds the output string r (double) – Value to convert to dms-representation pos (int) – Character denoting positive direction, typically ‘N’ or ‘E’. neg (int) – Character denoting negative direction, typically ‘S’ or ‘W’. char* Pointer to output buffer (same as s)
PJ_COORD proj_geocentric_latitude(const PJ *P, PJ_DIRECTION direction, PJ_COORD coord)

Convert from geographical latitude to geocentric latitude.

Parameters: P (const PJ*) – Transformation object direction (PJ_DIRECTION) – Starting direction of transformation coord (PJ_COORD) – Coordinate PJ_COORD Converted coordinate
int proj_angular_input(PJ *P, enum PJ_DIRECTION dir)

Check if a operation expects angular input.

Parameters: P (const PJ*) – Transformation object direction (PJ_DIRECTION) – Starting direction of transformation int 1 if angular input is expected, otherwise 0
int proj_angular_output(PJ *P, enum PJ_DIRECTION dir)

Check if an operation returns angular output.

param P: type P: Transformation object const PJ* Starting direction of transformation PJ_DIRECTION int 1 if angular output is returned, otherwise 0