NETGeographicLib::AlbersEqualArea Class Reference

.NET Wrapper for GeographicLib::AlbersEqualArea. More...

#include <NETGeographicLib/AlbersEqualArea.h>

List of all members.

Public Types

enum  StandardTypes { CylindricalEqualArea, AzimuthalEqualAreaNorth, AzimuthalEqualAreaSouth }

Public Member Functions

 ~AlbersEqualArea ()
 Destructor.
 AlbersEqualArea (StandardTypes type)
 AlbersEqualArea (double a, double f, double stdlat, double k0)
 AlbersEqualArea (double a, double f, double stdlat1, double stdlat2, double k1)
 AlbersEqualArea (double a, double f, double sinlat1, double coslat1, double sinlat2, double coslat2, double k1)
void SetScale (double lat, double k)
void Forward (double lon0, double lat, double lon,[System::Runtime::InteropServices::Out] double% x,[System::Runtime::InteropServices::Out] double% y,[System::Runtime::InteropServices::Out] double% gamma,[System::Runtime::InteropServices::Out] double% k)
void Reverse (double lon0, double x, double y,[System::Runtime::InteropServices::Out] double% lat,[System::Runtime::InteropServices::Out] double% lon,[System::Runtime::InteropServices::Out] double% gamma,[System::Runtime::InteropServices::Out] double% k)
void Forward (double lon0, double lat, double lon,[System::Runtime::InteropServices::Out] double% x,[System::Runtime::InteropServices::Out] double% y)
void Reverse (double lon0, double x, double y,[System::Runtime::InteropServices::Out] double% lat,[System::Runtime::InteropServices::Out] double% lon)

Properties

Inspector functions



double MajorRadius [get]
double Flattening [get]
double OriginLatitude [get]
double CentralScale [get]

Detailed Description

.NET Wrapper for GeographicLib::AlbersEqualArea.

This class allows .NET applications to access GeographicLib::AlbersEqualArea

Implementation taken from the report,

This is a implementation of the equations in Snyder except that divided differences will be [have been] used to transform the expressions into ones which may be evaluated accurately. [In this implementation, the projection correctly becomes the cylindrical equal area or the azimuthal equal area projection when the standard latitude is the equator or a pole.]

The ellipsoid parameters, the standard parallels, and the scale on the standard parallels are set in the constructor. Internally, the case with two standard parallels is converted into a single standard parallel, the latitude of minimum azimuthal scale, with an azimuthal scale specified on this parallel. This latitude is also used as the latitude of origin which is returned by AlbersEqualArea::OriginLatitude. The azimuthal scale on the latitude of origin is given by AlbersEqualArea::CentralScale. The case with two standard parallels at opposite poles is singular and is disallowed. The central meridian (which is a trivial shift of the longitude) is specified as the lon0 argument of the AlbersEqualArea::Forward and AlbersEqualArea::Reverse functions. AlbersEqualArea::Forward and AlbersEqualArea::Reverse also return the meridian convergence, , and azimuthal scale, k. A small square aligned with the cardinal directions is projected to a rectangle with dimensions k (in the E-W direction) and 1/k (in the N-S direction). The E-W sides of the rectangle are oriented degrees counter-clockwise from the x axis. There is no provision in this class for specifying a false easting or false northing or a different latitude of origin.

C# Example:

using System;
using NETGeographicLib;

namespace example_AlbersEqualArea
{
    class Program
    {
        static void Main(string[] args)
        {
            try {
                const double
                    lat1 = 40 + 58/60.0, lat2 = 39 + 56/60.0, // standard parallels
                    k1 = 1,                                   // scale
                    lon0 = -77 - 45/60.0;                     // Central meridan
                // Set up basic projection
                AlbersEqualArea albers = new AlbersEqualArea( Constants.WGS84.MajorRadius,
                                                              Constants.WGS84.Flattening,
                                                              lat1, lat2, k1);
                {
                    // Sample conversion from geodetic to Albers Equal Area
                    double lat = 39.95, lon = -75.17;    // Philadelphia
                    double x, y;
                    albers.Forward(lon0, lat, lon, out x, out y);
                    Console.WriteLine( String.Format("X: {0} Y: {1}", x, y ) );
                }
                {
                    // Sample conversion from Albers Equal Area grid to geodetic
                    double x = 220e3, y = -53e3;
                    double lat, lon;
                    albers.Reverse(lon0, x, y, out lat, out lon);
                    Console.WriteLine( String.Format("Latitude: {0} Longitude: {1}", lat, lon ) );
                }
            }
            catch (GeographicErr e) {
                Console.WriteLine( String.Format( "Caught exception: {0}", e.Message ) );
            }
        }
    }
}

Managed C++ Example:

using namespace System;
using namespace NETGeographicLib;

int main(array<System::String ^> ^/*args*/)
{
    try {
        const double
            lat1 = 40 + 58/60.0, lat2 = 39 + 56/60.0, // standard parallels
            k1 = 1,                                   // scale
            lon0 = -77 - 45/60.0;                     // Central meridan
        // Set up basic projection
        AlbersEqualArea^ albers = gcnew AlbersEqualArea( Constants::WGS84::MajorRadius,
                                                         Constants::WGS84::Flattening,
                                                         lat1, lat2, k1);
        {
            // Sample conversion from geodetic to Albers Equal Area
            double lat = 39.95, lon = -75.17;    // Philadelphia
            double x, y;
            albers->Forward(lon0, lat, lon, x, y);
            Console::WriteLine( String::Format("X: {0} Y: {1}", x, y ) );
        }
        {
            // Sample conversion from Albers Equal Area grid to geodetic
            double x = 220e3, y = -53e3;
            double lat, lon;
            albers->Reverse(lon0, x, y, lat, lon);
            Console::WriteLine( String::Format("Latitude: {0} Longitude: {1}", lat, lon ) );
        }
    }
    catch (GeographicErr^ e) {
        Console::WriteLine( String::Format( "Caught exception: {0}", e->Message ) );
        return -1;
    }
    return 0;
}

Visual Basic Example:

Imports NETGeographicLib

Module example_AlbersEqualArea
    Sub Main()
        Try
            Dim lat1 As Double = 40 + 58 / 60.0 : Dim lat2 As Double = 39 + 56 / 60.0 ' standard parallels
            Dim k1 As Double = 1  ' scale
            Dim lon0 As Double = -77 - 45 / 60.0 ' Central meridan
            ' Set up basic projection
            Dim albers As AlbersEqualArea = New AlbersEqualArea(Constants.WGS84.MajorRadius,
                                                                Constants.WGS84.Flattening,
                                                                lat1, lat2, k1)
            ' Sample conversion from geodetic to Albers Equal Area
            Dim lat As Double = 39.95 : Dim lon As Double = -75.17  ' Philadelphia
            Dim x, y As Double
            albers.Forward(lon0, lat, lon, x, y)
            Console.WriteLine(String.Format("X: {0} Y: {1}", x, y))
            ' Sample conversion from Albers Equal Area grid to geodetic
            x = 220000.0 : y = -53000.0
            albers.Reverse(lon0, x, y, lat, lon)
            Console.WriteLine(String.Format("Latitude: {0} Longitude: {1}", lat, lon))
        Catch ex As GeographicErr
            Console.WriteLine(String.Format("Caught exception: {0}", ex.Message))
        End Try
    End Sub
End Module

INTERFACE DIFFERENCES:
A constructor has been provided that creates the standard projections.

The MajorRadius, Flattening, OriginLatitude, and CentralScale functions are implemented as properties.

Definition at line 67 of file AlbersEqualArea.h.


Member Enumeration Documentation

Standard AlbersEqualAreaProjections that assume the WGS84 ellipsoid.

Enumerator:
CylindricalEqualArea 

cylindrical equal area projection (stdlat = 0, and k0 = 1)

AzimuthalEqualAreaNorth 

Lambert azimuthal equal area projection (stdlat = 90, and k0 = 1).

AzimuthalEqualAreaSouth 

Lambert azimuthal equal area projection (stdlat = 90, and k0 = 1).

Definition at line 79 of file AlbersEqualArea.h.


Constructor & Destructor Documentation

NETGeographicLib::AlbersEqualArea::~AlbersEqualArea (  )  [inline]

Destructor.

Definition at line 87 of file AlbersEqualArea.h.

References AlbersEqualArea().

NETGeographicLib::AlbersEqualArea::AlbersEqualArea ( StandardTypes  type  ) 

! Constructor for one of the standard types.

Parameters:
[in] type The desired standard type.

Referenced by ~AlbersEqualArea().

NETGeographicLib::AlbersEqualArea::AlbersEqualArea ( double  a,
double  f,
double  stdlat,
double  k0 
)

Constructor with a single standard parallel.

Parameters:
[in] a equatorial radius of ellipsoid (meters).
[in] f flattening of ellipsoid. Setting f = 0 gives a sphere. Negative f gives a prolate ellipsoid. If f > 1, set flattening to 1/f.
[in] stdlat standard parallel (degrees), the circle of tangency.
[in] k0 azimuthal scale on the standard parallel.
Exceptions:
GeographicErr if a, (1 f ) a, or k0 is not positive.
GeographicErr if stdlat is not in [90, 90].
NETGeographicLib::AlbersEqualArea::AlbersEqualArea ( double  a,
double  f,
double  stdlat1,
double  stdlat2,
double  k1 
)

Constructor with two standard parallels.

Parameters:
[in] a equatorial radius of ellipsoid (meters).
[in] f flattening of ellipsoid. Setting f = 0 gives a sphere. Negative f gives a prolate ellipsoid. If f > 1, set flattening to 1/f.
[in] stdlat1 first standard parallel (degrees).
[in] stdlat2 second standard parallel (degrees).
[in] k1 azimuthal scale on the standard parallels.
Exceptions:
GeographicErr if a, (1 f ) a, or k1 is not positive.
GeographicErr if stdlat1 or stdlat2 is not in [90, 90], or if stdlat1 and stdlat2 are opposite poles.
NETGeographicLib::AlbersEqualArea::AlbersEqualArea ( double  a,
double  f,
double  sinlat1,
double  coslat1,
double  sinlat2,
double  coslat2,
double  k1 
)

Constructor with two standard parallels specified by sines and cosines.

Parameters:
[in] a equatorial radius of ellipsoid (meters).
[in] f flattening of ellipsoid. Setting f = 0 gives a sphere. Negative f gives a prolate ellipsoid. If f > 1, set flattening to 1/f.
[in] sinlat1 sine of first standard parallel.
[in] coslat1 cosine of first standard parallel.
[in] sinlat2 sine of second standard parallel.
[in] coslat2 cosine of second standard parallel.
[in] k1 azimuthal scale on the standard parallels.
Exceptions:
GeographicErr if a, (1 f ) a, or k1 is not positive.
GeographicErr if stdlat1 or stdlat2 is not in [90, 90], or if stdlat1 and stdlat2 are opposite poles.

This allows parallels close to the poles to be specified accurately. This routine computes the latitude of origin and the azimuthal scale at this latitude. If dlat = abs(lat2 lat1) 160, then the error in the latitude of origin is less than 4.5 1014d;.


Member Function Documentation

void NETGeographicLib::AlbersEqualArea::SetScale ( double  lat,
double  k 
)

Set the azimuthal scale for the projection.

Parameters:
[in] lat (degrees).
[in] k azimuthal scale at latitude lat (default 1).
Exceptions:
GeographicErr k is not positive.
GeographicErr if lat is not in (90, 90).

This allows a "latitude of conformality" to be specified.

void NETGeographicLib::AlbersEqualArea::Forward ( double  lon0,
double  lat,
double  lon,
[System::Runtime::InteropServices::Out] double%   x,
[System::Runtime::InteropServices::Out] double%   y,
[System::Runtime::InteropServices::Out] double%   gamma,
[System::Runtime::InteropServices::Out] double%   k 
)

Forward projection, from geographic to Lambert conformal conic.

Parameters:
[in] lon0 central meridian longitude (degrees).
[in] lat latitude of point (degrees).
[in] lon longitude of point (degrees).
[out] x easting of point (meters).
[out] y northing of point (meters).
[out] gamma meridian convergence at point (degrees).
[out] k azimuthal scale of projection at point; the radial scale is the 1/k.

The latitude origin is given by AlbersEqualArea::LatitudeOrigin(). No false easting or northing is added and lat should be in the range [90, 90]; lon and lon0 should be in the range [540, 540). The values of x and y returned for points which project to infinity (i.e., one or both of the poles) will be large but finite.

void NETGeographicLib::AlbersEqualArea::Reverse ( double  lon0,
double  x,
double  y,
[System::Runtime::InteropServices::Out] double%   lat,
[System::Runtime::InteropServices::Out] double%   lon,
[System::Runtime::InteropServices::Out] double%   gamma,
[System::Runtime::InteropServices::Out] double%   k 
)

Reverse projection, from Lambert conformal conic to geographic.

Parameters:
[in] lon0 central meridian longitude (degrees).
[in] x easting of point (meters).
[in] y northing of point (meters).
[out] lat latitude of point (degrees).
[out] lon longitude of point (degrees).
[out] gamma meridian convergence at point (degrees).
[out] k azimuthal scale of projection at point; the radial scale is the 1/k.

The latitude origin is given by AlbersEqualArea::LatitudeOrigin(). No false easting or northing is added. lon0 should be in the range [540, 540). The value of lon returned is in the range [180, 180). The value of lat returned is in the range [90, 90]. If the input point is outside the legal projected space the nearest pole is returned.

void NETGeographicLib::AlbersEqualArea::Forward ( double  lon0,
double  lat,
double  lon,
[System::Runtime::InteropServices::Out] double%   x,
[System::Runtime::InteropServices::Out] double%   y 
)

AlbersEqualArea::Forward without returning the convergence and scale.

void NETGeographicLib::AlbersEqualArea::Reverse ( double  lon0,
double  x,
double  y,
[System::Runtime::InteropServices::Out] double%   lat,
[System::Runtime::InteropServices::Out] double%   lon 
)

AlbersEqualArea::Reverse without returning the convergence and scale.


Property Documentation

double NETGeographicLib::AlbersEqualArea::MajorRadius [get]
Returns:
a the equatorial radius of the ellipsoid (meters). This is the value used in the constructor.

Definition at line 245 of file AlbersEqualArea.h.

double NETGeographicLib::AlbersEqualArea::Flattening [get]
Returns:
f the flattening of the ellipsoid. This is the value used in the constructor.

Definition at line 251 of file AlbersEqualArea.h.

double NETGeographicLib::AlbersEqualArea::OriginLatitude [get]
Returns:
latitude of the origin for the projection (degrees).

This is the latitude of minimum azimuthal scale and equals the stdlat in the 1-parallel constructor and lies between stdlat1 and stdlat2 in the 2-parallel constructors.

Definition at line 260 of file AlbersEqualArea.h.

double NETGeographicLib::AlbersEqualArea::CentralScale [get]
Returns:
central scale for the projection. This is the azimuthal scale on the latitude of origin.

Definition at line 266 of file AlbersEqualArea.h.


The documentation for this class was generated from the following file:
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