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lookAtSpheroid

Line of sight intersection with oblate spheroid

Description

example

[lat,lon,slantrange] = lookAtSpheroid(lat0,lon0,h0,az,tilt,spheroid) computes the latitude and longitude (lat and lon) of the first point of intersection of the line-of-sight from a viewpoint in space with the surface of an oblate spheroid. If the line-of-sight does not intersect with the spheroid, lat and lon contain NaNs.

lat0 and lon0 are the geodetic coordinates of the viewpoint on the reference spheroid, spheroid. h0 specifies the geodetic height of the viewpoint in space above the spheroid. The az and tilt arguments specify the direction of the view (line-of-sight) as the azimuth angle, measured clockwise from North, and a tilt angle. The following figure illustrates these measurements. The optional slantrange output argument returns the (3-D Euclidean) distance from the viewpoint to the intersection. All angles are in degrees.

Examples

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Create a reference spheroid. Specify the length unit as kilometers.

spheroid = wgs84Ellipsoid('km');

Define location of view in space. The units for h0 match the units of the spheroid (kilometers).

lat0 = 0;
lon0 = -100;
h0 = 35786;

Define the view from space in terms of the azimuth angle and tilt.

az = 45;
tilt = 6;

Calculate the point on the spheroid at which the view first intersects with the spheroid. The example also returns the distance in kilometers between the viewpoint in space and the first point of intersection with the spheroid.

[lat,lon,slantrange] = lookAtSpheroid(lat0,lon0,h0,az,tilt,spheroid)
lat = 25.7991
lon = -71.3039
slantrange = 3.7328e+04

Input Arguments

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Geodetic latitude of the viewpoint on the spheroid, specified as a scalar value, vector, matrix, or N-D array.

Data Types: single | double

Geodetic longitude of the viewpoint on the spheroid, specified as a scalar value, vector, matrix, or N-D array.

Data Types: single | double

Height of the viewpoint in space above the spheroid, specified as a scalar value, vector, matrix, or N-D array. h0 must be in units that match the spheroid input.

Data Types: single | double

Azimuth angle of view from space, specified as a scalar value, vector, matrix, or N-D array. Measured in degrees, clockwise from north.

Data Types: single | double

Tilt angle of view from space, specified as scalar value, vector, matrix, or N-D array. Measured in degrees, relative to a vector pointing downward toward the nadir point. The nadir point is the point on the spheroid directly below the viewpoint, with geodetic coordinates (lat0, lon0, 0). When the tilt is zero (0), the line-of-sight is directed at the nadir point itself. Tilt can be in the range [0 180] but for large angles and all angles greater than or equal to 90 degrees, there is no intersection with the spheroid.

Data Types: single | double

Reference spheroid, specified as a referenceEllipsoid, oblateSpheroid, or referenceSphere object. Use the constructor for one of these three classes, or the wgs84Ellipsoid function, to construct a spheroid object. You cannot directly pass in the name of the reference spheroid. Instead, pass the name to referenceEllipsoid or referenceSphere and use the resulting object.

Output Arguments

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Latitude of the first point of intersection with the spheroid, returned as a scalar value, vector, matrix, or N-D array. If the line-of-sight does not intersect with the spheroid, lat contains NaNs.

Longitude of the first point of intersection with the spheroid, returned as a scalar value, vector, matrix, or N-D array. If the line-of-sight does not intersect with the spheroid, lon contains NaNs.

Distance from the viewpoint to the intersection with the spheroid, returned as a scalar value, vector, matrix, or N-D array. Units match the LengthUnit property of the input spheroid object. 