ref: 1dbb193077af7ba6ff7fb70a4dd465480764382e
dir: /man/2/geodesy/
.TH GEODESY 2
.SH NAME
geodesy \- Geodesy module
.SH SYNOPSIS
.EX
include "geodesy.m";
geodesy := load Geodesy Geodesy->PATH;
# easting, northing
Eano: adt{
e: real;
n: real;
};
# latitude, longitude in radians
Lalo: adt{
la: real;
lo: real;
};
OSGB36, Ireland65, ED50, WGS84, ITRS2000, ETRS89: con iota;
Natgrid, IrishNatgrid, UTMEur, UTM: con iota;
init: fn(d: int, t: int, z: int);
format: fn(d: int, t: int, z: int);
os2en: fn(s: string): (int, Eano);
en2os: fn(en: Eano): string;
str2lalo: fn(s: string): (int, Lalo);
lalo2str: fn(lalo: Lalo): string;
str2en: fn(s: string): (int, Eano);
en2lalo: fn(en: Eano): Lalo;
lalo2en: fn(lalo: Lalo): Eano;
datum2datum: fn(lalo: Lalo, f: int, t: int): Lalo;
.EE
.SH DESCRIPTION
.B Geodesy
provides routines to deal with (some) terrestrial coordinate systems.
.PP
Eastings and northings are defined by the
.B Eano
adt and are measured in metres and latitude and longitude (which should be in radians) by the
.B Lalo
adt. Latitude is in the range -π/2 to π/2 radians and longitude in the
range -π to π radians.
.PP
.B OSGB36
(Ordnance Survey Great Britain 1936),
.B Ireland65
(Ireland 1965),
.B ED50
(European Datum 1950),
.B WGS84
(World Geodetic System 1984),
.B ITRS2000
(International Terrestrial Reference System 2000), and
.B ETRS89
(European Terrestrial Reference System 1989) are the current datums defined. Helmert transformations are used
to convert between them. Note that
.B Ireland65
and
.B ED50
are currently not supported and
.B WGS84
and
.B ITRS2000
are considered equivalent.
.PP
.B Natgrid
(National Grid),
.B IrishNatgrid
(Irish National Grid),
.B UTMEur
(European Universal Transverse Mercator), and
.B UTM
(Universal Transverse Mercator) are the current transverse Mercator projections supported.
.PP
The following functions are provided
.TP
.B init
The module should always be initialized first. The parameters are
the required datum (default WGS84), transverse Mercator projection (default Natgrid) and UTM zone (default 30) if appropriate. Negative values or out of range values are
ignored.
.TP
.B format
Parameters as above. Alters the current settings at any time though care
must be taken to ensure existing coordinates are still treated as in their
original form.
.TP
.B os2en
Converts an Ordnance Survey National Grid reference to an easting, northing.
The formats XYen, XYeenn, XYeeennn, XYeeeennnn, XYeeeeennnnn, eenn,
eeennn, eeeennnn, eeeeennnnn and eeeeeennnnnn are allowed. Here X and
Y are upper case letters, e is an easting digit and n is a northing digit. The
reference can therefore be rounded to the nearest decakilometre, kilometre,
hectometre, decametre or metre. The first element of the returned tuple is zero
if the string has an incorrect format.
.TP
.B en2os
Converts an easting, northing to an OS reference in the form XYeeeeennnnn
as above.
.TP
.B str2lalo
Converts a latitude/longitude string to a latitude, longitude. The string
may have the formats deg[N|S], deg:min[N|S] or deg:min:sec[N|S] for
latitude, deg[E|W], deg:min[E|W] or deg:min:sec[E|W] for longitude. The
latitude must come first, then optional white space, then the longitude.
Degrees, minutes and seconds may be integer or real. Format errors
are indicated as in
.B os2en.
.TP
.B lalo2str
Converts a latitude, longitude to string format as above. Seconds are given
to two decimal places.
.TP
.B str2en
Converts a string in OS or latitude/longitude format as above to an easting, northing.
Format errors indicated as in
.B os2en.
.TP
.B en2lalo
Converts an easting, northing to latitude, longitude using the current transverse
Mercator projection.If the latter is
.B UTM
or
.B UTMEur
the current zone setting will be used.
.TP
.B lalo2en
Converts latitude, longitude to an easting, northing using the current transverse
Mercator projection.
.TP
datum2datum
Approximate (Helmert) transformation of a latitude, longitude between any of
.B OSGB36,
.B WGS84,
.B ITRS2000
or
.B ETRS89.
The `from' datum appears first in the parameter list.
.SH SOURCE
.B /module/math/geodesy.m
.br
.B /appl/math/geodesy.b
.SH BUGS
The module is heavily biased towards Great Britain.