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|
package ellipsoid
// Written in Go by Stefan Schroeder, New York, 2013
// Version 1.0 based on Geo::Ellipsoid Version 1.12.
// Version 1.1 Added ECEF functions.
// Version 1.2 Replaced Fabs with Abs.
// Version 1.3 Added Displacement function
/*
SYNOPSIS
See hello-world.go example.
DESCRIPTION
ellipsoid performs geometrical calculations on the surface of
an ellipsoid. An ellipsoid is a three-dimension object formed from
the rotation of an ellipse about one of its axes. The approximate
shape of the earth is an ellipsoid, so ellipsoid can accurately
calculate distance and bearing between two widely-separated locations
on the earth's surface.
The shape of an ellipsoid is defined by the lengths of its
semi-major and semi-minor axes. The shape may also be specifed by
the flattening ratio f as:
f = ( semi-major - semi-minor ) / semi-major
which, since f is a small number, is normally given as the reciprocal
of the flattening 1/f.
The shape of the earth has been surveyed and estimated differently
at different times over the years. The two most common sets of values
used to describe the size and shape of the earth in the United States
are 'NAD27', dating from 1927, and 'WGS84', from 1984. United States
Geological Survey topographical maps, for example, use one or the
other of these values, and commonly-available Global Positioning
System (GPS) units can be set to use one or the other.
See "DEFINED ELLIPSOIDS" below for the ellipsoid survey values
that may be selected for use by ellipsoid.
*/
import "math"
import "fmt"
const (
pi = math.Pi
twopi = math.Pi * 2.0
maxLoopCount = 20
eps = 1.0e-23
debug = false
// Meter is one of the output/input units.
Meter = 0 // 1.0 meter
// Foot is one of the output/input units.
Foot = 1 // 0.3048 meter are a foot
// Kilometer is one of the output/input units.
Kilometer = 2 // 1000.0 meter are a kilometer
// Mile is one of the output/input units.
Mile = 3 // 1609.344 meter are a mile
// Nm (nautical mile) is one of the output/input units.
Nm = 4 // 1852.0 meter are a nautical mile,
// Degrees is one of the possible angle units for input/output.
Degrees = iota
// Radians is one of the possible angle units for input/output.
Radians = iota
// LongitudeIsSymmetric determines that the output longitude shall be symmetric.
LongitudeIsSymmetric = true
// LongitudeNotSymmetric determines that the output longitude shall not be symmetric.
LongitudeNotSymmetric = false
// BearingIsSymmetric determines that the output bearing shall be symmetric.
BearingIsSymmetric = true
// BearingNotSymmetric determines that the output bearing shall not be symmetric.
BearingNotSymmetric = false
)
// Ellipsoid is the main object to store information about one ellispoid.
type Ellipsoid struct {
Ellipse ellipse
Units int
DistanceUnits int
LongitudeSymmetric bool
BearingSymmetry bool
DistanceFactor float64
// Having the DistanceFactor AND the DistanceUnits in this struct is redundant
// but it looks nicer in the code.
}
type ellipse struct {
Equatorial float64
InvFlattening float64
}
// Location is one coordinate in LLA.
type Location struct {
Lat float64
Lon float64
Ele float64
}
func deg2rad(d float64) (r float64) {
return d * pi / 180.0
}
func rad2deg(d float64) (r float64) {
return d * 180.0 / pi
}
/* Init
The Init constructor must be called with a list of parameters to set
the value of the ellipsoid to be used, the value of the units to be
used for angles and distances, and whether or not the output range
of longitudes and bearing angles should be symmetric around zero
or always greater than zero. There is no default constructor, all
arguments are required; they may not be abbreviated.
Example:
geo := ellipsoid.Init(
"WGS84", // for possible values see below.
ellipsoid.Degrees, // possible values: Degrees or Radians
ellipsoid.Meter, // possible values: Meter, Kilometer,
// Foot, Nm, Mile
ellipsoid.LongitudeIsSymmetric, // possible values
// LongitudeIsSymmetric or
// LongitudeNotSymmetric
ellipsoid.BearingIsSymmetric // possible
// values BearingIsSymmetric or
// BearingNotSymmetric
)
*/
func Init(name string, units int, distUnits int, longSym bool, bearSym bool) (e Ellipsoid) {
m := map[string]ellipse{
"AIRY": {6377563.396, 299.3249646},
"AIRY-MODIFIED": {6377340.189, 299.3249646},
"AUSTRALIAN": {6378160.0, 298.25},
"BESSEL-1841": {6377397.155, 299.1528128},
"BESSEL-1841-NAMIBIA": {6377483.865, 299.152813},
"CLARKE-1866": {6378206.400, 294.978698},
"CLARKE-1880": {6378249.145, 293.465},
"EVEREST-1830": {6377276.345, 300.8017},
"EVEREST-1948": {6377304.063, 300.8017},
"EVEREST-SABAH-SARAWAK": {6377298.556, 300.801700},
"EVEREST-1956": {6377301.243, 300.801700},
"EVEREST-1969": {6377295.664, 300.801700},
"FISHER-1960": {6378166.0, 298.3},
"FISCHER-1960-MODIFIED": {6378155.000, 298.300000},
"FISHER-1968": {6378150.0, 298.3},
"GRS80": {6378137.0, 298.25722210088},
"HELMERT-1906": {6378200.000, 298.300000},
"HOUGH-1956": {6378270.0, 297.0},
"HAYFORD": {6378388.0, 297.0},
"IAU76": {6378140.0, 298.257},
"INTERNATIONAL": {6378388.000, 297.000000},
"KRASSOVSKY-1938": {6378245.0, 298.3},
"NAD27": {6378206.4, 294.9786982138},
"NWL-9D": {6378145.0, 298.25},
"SGS85": {6378136.000, 298.257000},
"SOUTHAMERICAN-1969": {6378160.0, 298.25},
"SOVIET-1985": {6378136.0, 298.257},
"WGS60": {6378165.000, 298.300000},
"WGS66": {6378145.000, 298.250000},
"WGS72": {6378135.0, 298.26},
"WGS84": {6378137.0, 298.257223563},
}
e2, ok := m[name]
if !ok {
fmt.Printf("ellipsoid.go: Warning: Invalid ellipse type '%v'\n", name)
}
// m ft km mi nm
conversion := []float64{1.0, 0.3048, 1000.0, 1609.344, 1852.0}
ellipsoid := Ellipsoid{e2, units, distUnits, longSym, bearSym, conversion[distUnits]}
return ellipsoid
}
/* Intermediate
Takes two coordinates with longitude and latitude; and a step count and
returns range and bearing and an array with the lons and lats of intermediate
points on a straight line (whatever that is on an ellipsoid), INCLUDING the
start and the endpoint.
So if you put in point1 and point2 with step count 4, the output will be
(you make 4 hops, right?)
point1
i1
i2
i3
point2
Each point is two float64 values, lat and lon, thus you have an array
with 4*2 + 2 = 5*2 cells.
steps shall not be 0.
I havent tested the upper limit for steps.
*/
func (ellipsoid Ellipsoid) Intermediate(lat1, lon1, lat2, lon2 float64, steps int) (distance, bearing float64, arr []float64) {
if steps == 0 {
return
}
r, phi := ellipsoid.To(lat1, lon1, lat2, lon2)
v := make([]float64, steps*2+2)
for i := 0; i <= steps; i++ {
a, b := ellipsoid.At(lat1, lon1, r*float64(i)/float64(steps), phi)
v[i*2], v[i*2+1] = a, b
}
arr = v
return r, phi, arr
}
/* To returns range, bearing between two specified locations.
dist, theta = geo.To( lat1, lon1, lat2, lon2 )
*/
func (ellipsoid Ellipsoid) To(lat1, lon1, lat2, lon2 float64) (distance, bearing float64) {
if ellipsoid.Units == Degrees {
lat1 = deg2rad(lat1)
lon1 = deg2rad(lon1)
lat2 = deg2rad(lat2)
lon2 = deg2rad(lon2)
}
distance, bearing = ellipsoid.calculateBearing(lat1, lon1, lat2, lon2)
if ellipsoid.Units == Degrees {
bearing = rad2deg(bearing)
}
distance /= ellipsoid.DistanceFactor
return
}
/* At returns the list latitude,longitude in degrees or radians that is a
specified range and bearing from a given location.
lat2, lon2 = geo.At( lat1, lon1, range, bearing )
*/
func (ellipsoid Ellipsoid) At(lat1, lon1, distance, bearing float64) (lat2, lon2 float64) {
if ellipsoid.Units == Degrees {
lat1 = deg2rad(lat1)
lon1 = deg2rad(lon1)
bearing = deg2rad(bearing)
}
lat2, lon2 = ellipsoid.calculateTargetlocation(lat1, lon1, distance, bearing)
if ellipsoid.LongitudeSymmetric == LongitudeIsSymmetric {
if lon2 > pi {
lon2 -= twopi
}
}
if ellipsoid.LongitudeSymmetric == LongitudeNotSymmetric {
if lon2 < 0.0 {
lon2 += twopi
}
}
if ellipsoid.Units == Degrees {
lat2 = rad2deg(lat2)
lon2 = rad2deg(lon2)
}
return
}
/* Displacement returns the (x,y) displacement in distance units between the two specified
locations.
x, y = geo.Displacement( lat1, lon1, lat2, lon2 )
NOTE: The x and y displacements are only approximations and only valid
between two locations that are fairly near to each other. Beyond 10 kilometers
or more, the concept of X and Y on a curved surface loses its meaning.
*/
func (ellipsoid Ellipsoid) Displacement(lat1, lon1, lat2, lon2 float64) (x, y float64) {
// FIXME: Normalize!!! before use.
r, bearing := ellipsoid.To(lat1, lon1, lat2, lon2)
if ellipsoid.Units == Degrees {
bearing = deg2rad(bearing)
}
x = r * math.Sin(bearing)
y = r * math.Cos(bearing)
return x, y
}
/* Location returns the list (latitude,longitude) of a location at a given (x,y)
displacement from a given location.
lat2, lon2 = geo.Location( lat1, lon1, x, y )
The note from Displacement applies.
*/
func (ellipsoid Ellipsoid) Location(lat1, lon1, x, y float64) (lat, lon float64) {
degreesPerRadian := 180.0 / math.Pi
range1 := math.Sqrt(x*x + y*y)
bearing1 := math.Atan2(x, y)
if ellipsoid.Units == Degrees {
bearing1 *= degreesPerRadian
}
return ellipsoid.At(lat1, lon1, range1, bearing1)
}
func (ellipsoid Ellipsoid) calculateTargetlocation(lat1, lon1, distance, bearing float64) (lat2, lon2 float64) {
if debug == true {
fmt.Printf("_forward(lat1=%v,lon1=%v,range=%v,bearing=%v)\n", lat1, lon1, distance, bearing)
}
eps := 0.5e-13
a := ellipsoid.Ellipse.Equatorial
f := 1.0 / ellipsoid.Ellipse.InvFlattening
r := 1.0 - f
clat1 := math.Cos(lat1)
if clat1 == 0 {
fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
return 0.0, 0.0
}
tu := r * math.Sin(lat1) / clat1
faz := bearing
s := ellipsoid.DistanceFactor * distance
sf := math.Sin(faz)
cf := math.Cos(faz)
baz := 0.0
if cf != 0.0 {
baz = 2.0 * math.Atan2(tu, cf)
}
cu := 1.0 / math.Sqrt(1.0+tu*tu)
su := tu * cu
sa := cu * sf
c2a := 1.0 - (sa * sa)
x := 1.0 + math.Sqrt((((1.0/(r*r))-1.0)*c2a)+1.0)
x = (x - 2.0) / x
c := 1.0 - x
c = (((x * x) / 4.0) + 1.0) / c
d := x * ((0.375 * x * x) - 1.0)
tu = ((s / r) / a) / c
y := tu
if debug == true {
fmt.Printf("r=%.8f, tu=%.8f, faz=%.8f\n", r, tu, faz)
fmt.Printf("baz=%.8f, sf=%.8f, cf=%.8f\n", baz, sf, cf)
fmt.Printf("cu=%.8f, su=%.8f, sa=%.8f\n", cu, su, sa)
fmt.Printf("x=%.8f, c=%.8f, y=%.8f\n", x, c, y)
}
var cy, cz, e, sy float64
for true {
sy = math.Sin(y)
cy = math.Cos(y)
cz = math.Cos(baz + y)
e = (2.0 * cz * cz) - 1.0
c = y
x = e * cy
y = (2.0 * e) - 1.0
y = (((((((((sy * sy * 4.0) - 3.0) * y * cz * d) / 6.0) + x) * d) / 4.0) - cz) * sy * d) + tu
if math.Abs(y-c) <= eps {
break
}
}
baz = (cu * cy * cf) - (su * sy)
c = r * math.Sqrt((sa*sa)+(baz*baz))
d = su*cy + cu*sy*cf
lat2 = math.Atan2(d, c)
c = cu*cy - su*sy*cf
x = math.Atan2(sy*sf, c)
c = (((((-3.0 * c2a) + 4.0) * f) + 4.0) * c2a * f) / 16.0
d = ((((e * cy * c) + cz) * sy * c) + y) * sa
lon2 = lon1 + x - (1.0-c)*d*f
if debug == true {
fmt.Printf("returns(lat2=%v,lon2=%v)\n", lat2, lon2)
}
return lat2, lon2
}
func (ellipsoid Ellipsoid) calculateBearing(lat1, lon1, lat2, lon2 float64) (distance, bearing float64) {
a := ellipsoid.Ellipse.Equatorial
f := 1 / ellipsoid.Ellipse.InvFlattening
if lon1 < 0 {
lon1 += twopi
}
if lon2 < 0 {
lon2 += twopi
}
r := 1.0 - f
clat1 := math.Cos(lat1)
if clat1 == 0 {
fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
return 0.0, 0.0
}
clat2 := math.Cos(lat2)
if clat2 == 0 {
fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
return 0.0, 0.0
}
tu1 := r * math.Sin(lat1) / clat1
tu2 := r * math.Sin(lat2) / clat2
cu1 := 1.0 / (math.Sqrt((tu1 * tu1) + 1.0))
su1 := cu1 * tu1
cu2 := 1.0 / (math.Sqrt((tu2 * tu2) + 1.0))
s := cu1 * cu2
baz := s * tu2
faz := baz * tu1
dlon := lon2 - lon1
if debug == true {
fmt.Printf("a=%v, f=%v\n", a, f)
fmt.Printf("lat1=%v, lon1=%v\n", lat1, lon1)
fmt.Printf("lat2=%v, lon2=%v\n", lat2, lon2)
fmt.Printf("r=%v, tu1=%v, tu2=%v\n", r, tu1, tu2)
fmt.Printf("faz=%.8f, dlon=%.8f, su1=%v\n", faz, dlon, su1)
}
x := dlon
cnt := 0
var c2a, c, cx, cy, cz, d, del, e, sx, sy, y float64
// This originally was a do-while loop. Exit condition is at end of loop.
for true {
if debug == true {
fmt.Printf(" x=%.8f\n", x)
}
sx = math.Sin(x)
cx = math.Cos(x)
tu1 = cu2 * sx
tu2 = baz - (su1 * cu2 * cx)
if debug == true {
fmt.Printf(" sx=%.8f, cx=%.8f, tu1=%.8f, tu2=%.8f\n", sx, cx, tu1, tu2)
}
sy = math.Sqrt(tu1*tu1 + tu2*tu2)
cy = s*cx + faz
y = math.Atan2(sy, cy)
var sa float64
if sy == 0.0 {
sa = 1.0
} else {
sa = (s * sx) / sy
}
if debug == true {
fmt.Printf(" sy=%.8f, cy=%.8f, y=%.8f, sa=%.8f\n", sy, cy, y, sa)
}
c2a = 1.0 - (sa * sa)
cz = faz + faz
if c2a > 0.0 {
cz = ((-cz) / c2a) + cy
}
e = (2.0 * cz * cz) - 1.0
c = (((((-3.0 * c2a) + 4.0) * f) + 4.0) * c2a * f) / 16.0
d = x
x = ((e*cy*c+cz)*sy*c + y) * sa
x = (1.0-c)*x*f + dlon
del = d - x
if debug == true {
fmt.Printf(" c2a=%.8f, cz=%.8f\n", c2a, cz)
fmt.Printf(" e=%.8f, d=%.8f\n", e, d)
fmt.Printf(" (d-x)=%.8g\n", del)
}
if math.Abs(del) <= eps {
break
}
cnt++
if cnt > maxLoopCount {
break
}
}
faz = math.Atan2(tu1, tu2)
baz = math.Atan2(cu1*sx, (baz*cx-su1*cu2)) + pi
x = math.Sqrt(((1.0/(r*r))-1.0)*c2a+1.0) + 1.0
x = (x - 2.0) / x
c = 1.0 - x
c = ((x*x)/4.0 + 1.0) / c
d = ((0.375 * x * x) - 1.0) * x
x = e * cy
if debug == true {
fmt.Printf("e=%.8f, cy=%.8f, x=%.8f\n", e, cy, x)
fmt.Printf("sy=%.8f, c=%.8f, d=%.8f\n", sy, c, d)
fmt.Printf("cz=%.8f, a=%.8f, r=%.8f\n", cz, a, r)
}
s = 1.0 - e - e
s = ((((((((sy * sy * 4.0) - 3.0) * s * cz * d / 6.0) - x) * d / 4.0) + cz) * sy * d) + y) * c * a * r
if debug == true {
fmt.Printf("s=%.8f\n", s)
}
// adjust azimuth to (0,360) or (-180,180) as specified
if ellipsoid.BearingSymmetry == BearingIsSymmetric {
if faz < -(pi) {
faz += twopi
}
if faz >= pi {
faz -= twopi
}
} else {
if faz < 0 {
faz += twopi
}
if faz >= twopi {
faz -= twopi
}
}
distance, bearing = s, faz
return
}
/* ToLLA takes three cartesian coordinates x, y, z and returns
the latitude, longitude, elevation list.
FIXME: This algorithm cannot handle x==0, although this is a valid value.
WARNING: I put in an if condition to catch this. Is it still necessary?
*/
func (ellipsoid Ellipsoid) ToLLA(x, y, z float64) (lat1, lon1, alt1 float64) {
if x == 0 {
fmt.Printf("FATAL: Caught x==0 (div by zero).\n")
return
}
a := ellipsoid.Ellipse.Equatorial
f := 1 / ellipsoid.Ellipse.InvFlattening
b := a * (1.0 - f)
e := math.Sqrt((a*a - b*b) / (a * a))
e2 := math.Sqrt((a*a - b*b) / (b * b)) // e'
esq := e * e // e squared
e2sq := e2 * e2 // e' squared
p := math.Sqrt(x*x + y*y)
theta := math.Atan2(z*a, p*b)
stheta3 := math.Sin(theta) * math.Sin(theta) * math.Sin(theta)
ctheta3 := math.Cos(theta) * math.Cos(theta) * math.Cos(theta)
lon1 = math.Atan2(y, x)
phi := math.Atan2(z+e2sq*b*stheta3, p-esq*a*ctheta3)
lat1 = phi
sphisq := math.Sin(phi) * math.Sin(phi)
N := a / (math.Sqrt(1 - esq*sphisq))
alt1 = p/math.Cos(phi) - N
if ellipsoid.LongitudeSymmetric == LongitudeIsSymmetric {
if lon1 > pi {
lon1 -= twopi
}
}
if ellipsoid.LongitudeSymmetric == LongitudeNotSymmetric {
if lon1 < 0.0 {
lon1 += twopi
}
}
if ellipsoid.Units == Degrees {
lat1 = rad2deg(lat1)
lon1 = rad2deg(lon1)
}
return lat1, lon1, alt1
}
/* ToECEF takes the latitude, longitude, elevation list and
returns three cartesian coordinates x, y, z */
func (ellipsoid Ellipsoid) ToECEF(lat1, lon1, alt1 float64) (x, y, z float64) {
a := ellipsoid.Ellipse.Equatorial
f := 1 / ellipsoid.Ellipse.InvFlattening
b := a * (1.0 - f)
e := math.Sqrt((a*a - b*b) / (a * a))
esq := e * e // e squared
if ellipsoid.Units == Degrees {
lat1 = deg2rad(lat1)
lon1 = deg2rad(lon1)
}
h := alt1 // renamed for convenience
phi := lat1
lambda := lon1
cphi := math.Cos(phi)
sphi := math.Sin(phi)
sphisq := sphi * sphi
clam := math.Cos(lambda)
slam := math.Sin(lambda)
N := a / (math.Sqrt(1 - esq*sphisq))
x = (N + h) * cphi * clam
y = (N + h) * cphi * slam
z = ((b*b*N)/(a*a) + h) * sphi
return x, y, z
}
/*
DEFINED ELLIPSOIDS
The following ellipsoids are defined in Geo::Ellipsoid, with the
semi-major axis in meters and the reciprocal flattening as shown.
Ellipsoid Semi-Major Axis (m.) 1/Flattening
--------- ------------------- ---------------
AIRY 6377563.396 299.3249646
AIRY-MODIFIED 6377340.189 299.3249646
AUSTRALIAN 6378160.0 298.25
BESSEL-1841 6377397.155 299.1528128
CLARKE-1880 6378249.145 293.465
EVEREST-1830 6377276.345 290.8017
EVEREST-MODIFIED 6377304.063 290.8017
FISHER-1960 6378166.0 298.3
FISHER-1968 6378150.0 298.3
GRS80 6378137.0 298.25722210088
HOUGH-1956 6378270.0 297.0
HAYFORD 6378388.0 297.0
IAU76 6378140.0 298.257
KRASSOVSKY-1938 6378245.0 298.3
NAD27 6378206.4 294.9786982138
NWL-9D 6378145.0 298.25
SOUTHAMERICAN-1969 6378160.0 298.25
SOVIET-1985 6378136.0 298.257
WGS72 6378135.0 298.26
WGS84 6378137.0 298.257223563
plus a few more ...
LIMITATIONS
The methods should not be used on points which are too near the poles
(above or below 89 degrees), and should not be used on points which
are antipodal, i.e., exactly on opposite sides of the ellipsoid. The
methods will not return valid results in these cases.
The Go-version does not support all features of the Perl module. If you
need advanced features, like defining your own ellipses at runtime,
calculating x,y dislocations, etc, please refer to the package on CPAN
Geo::Ellipsoid
http://search.cpan.org/~jgibson/Geo-Ellipsoid-1.12/lib/Geo/Ellipsoid.pm
FIXME: Add more checks for div by 0.
ACKNOWLEDGEMENTS
The conversion algorithms used here are Perl translations of Fortran
routines written by LCDR L. Pfeifer NGS Rockville MD that implement
T. Vincenty's Modified Rainsford's method with Helmert's elliptical
terms as published in "Direct and Inverse Solutions of Ellipsoid on
the Ellipsoid with Application of Nested Equations", T. Vincenty,
Survey Review, April 1975.
The Fortran source code files inverse.for and forward.for
may be obtained from
ftp://ftp.ngs.noaa.gov/pub/pcsoft/for_inv.3d/source/
AUTHOR
Jim Gibson, <Jim@Gibson.org> (Perl version)
Stefan Schroeder <ondekoza@gmail.com> (Port from Perl to Golang)
BUGS
See LIMITATIONS, above.
Please report any bugs or feature requests to
the author.
COPYRIGHT & LICENSE
Copyright 2005-2008 Jim Gibson, all rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl.
*/
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