ellipse1

Geographic ellipse from center, semimajor axis, eccentricity, and azimuth

Syntax

[lat,lon] = ellipse1(lat0,lon0,ellipse)

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset)

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az)

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az,ellipsoid)

[lat,lon] = ellipse1(___,units)

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az,ellipsoid,units,npts)

[lat,lon] = ellipse1(method,___)

mat = ellipse1(___)

Description

[lat,lon] = ellipse1(lat0,lon0,ellipse) finds the latitude and longitude coordinates of an ellipse. Specify the geographic coordinates of the center of the ellipse using lat0 and lon0. Specify the semimajor axis and the eccentricity of the ellipse using ellipse. This syntax assumes that the semimajor axis is a spherical distance in degrees. This syntax orients the ellipse so that the semimajor axis goes from north to south.

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset) rotates the ellipse using the azimuth offset offset.

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az) finds coordinates for the section of the ellipse specified by az.

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az,ellipsoid) specifies the reference ellipsoid ellipsoid to use for the coordinates. This syntax assumes that the semimajor axis of ellipse is a linear measurement in the same units as the semimajor axis of ellipsoid.

[lat,lon] = ellipse1(___,units) specifies the angle units units of the inputs and outputs. You can use this syntax with any of the previous syntaxes, except ellipse1(lat0,lon0,ellipse).

[lat,lon] = ellipse1(lat0,lon0,ellipse,offset,az,ellipsoid,units,npts) specifies the number of points npts to include in the ellipse.

[lat,lon] = ellipse1(method,___), where method is "rh", specifies that distances from the center of the small circle are rhumb line distances. The default for method is "gc", which specifies that distances from the center of the small circle are great circle distances (for a sphere) or geodesic distances (for an ellipsoid).

mat = ellipse1(___) returns the latitude and longitude coordinates of the ellipse in the matrix mat.

Examples

Find Coordinates of Ellipse

Find the latitude and longitude coordinates of an ellipse centered on Ottawa with a semimajor axis of 4º and a semiminor axis of 2º. Find the eccentricity of the ellipse by using the axes2ecc function.

lat0 = 45.4215;
lon0 = -75.6972;
semimajor = 4;
ecc = axes2ecc(semimajor,2);
[lat1,lon1] = ellipse1(lat0,lon0,[semimajor ecc]);

Find the latitude coordinates of the same ellipse, this time with the semimajor axis rotated 45º from north.

[lat2,lon2] = ellipse1(lat0,lon0,[semimajor ecc],45);

Plot both ellipses on a map using thick lines.

geoplot(lat1,lon1,LineWidth=2)
hold on
geoplot(lat2,lon2,LineWidth=2)
geobasemap streets

Find Coordinates of Partial Ellipse

Find the latitude and longitude coordinates of a full ellipse centered on Tokyo with a semimajor axis of 5º and a semiminor axis of 2º. Find the eccentricity of the ellipse by using the axes2ecc function.

lat0 = 35.6762;
lon0 = 139.6503;
semimajor = 5;
ecc = axes2ecc(semimajor,2);
[lat1,lon1] = ellipse1(lat0,lon0,[semimajor ecc]);

Find the coordinates of a partial ellipse, in this case the section of the ellipse between 90º from north and 270º from north. Avoid rotating the ellipse by specifying the fourth argument as [].

az = [90 270];
[lat2,lon2] = ellipse1(lat0,lon0,[semimajor ecc],[],az);

Display both the full ellipse and the partial ellipse on a map. Use a thick line for the partial ellipse.

geoplot(lat1,lon1,Color=[0.8500 0.3250 0.0980])
hold on
geoplot(lat2,lon2,Color=[0.4940 0.1840 0.5560],LineWidth=3)
geobasemap streets

Find Coordinates of Ellipse on Reference Ellipsoid

Create a World Geodetic System of 1984 (WGS84) reference ellipsoid with a length unit of kilometers.

wgs84 = wgs84Ellipsoid("km");

Find the latitude and longitude coordinates of an ellipse centered on Boston with a semimajor axis of 100 kilometers and a semiminor axis of 50 kilometers. Avoid rotating the ellipse and find the coordinates of the full ellipse by specifying the fourth and fifth arguments as []. Find the eccentricity of the ellipse by using the axes2ecc function.

lat0 = 42.3601;
lon0 = -71.0589;
semimajor = 100;
ecc = axes2ecc(100,50);
[lat,lon] = ellipse1(lat0,lon0,[semimajor ecc],[],[],wgs84);

Plot the ellipse on a map using a thick black line.

geoplot(lat,lon,"k",LineWidth=2)
geobasemap streets

Find Coordinates of Multiple Ellipses

You can use the ellipse1 function to find the coordinates of multiple ellipses with the same center or with different centers.

Multiple Ellipses with Same Center

Find the coordinates of three ellipses centered on Portland, Oregon.

• The first ellipse has a semimajor axis of 4º and a semiminor axis of 2º. Rotate the semimajor axis 50º from north.

• The second ellipse has a semimajor axis of 4.5º and a semiminor axis of 2.5º. Rotate the semimajor axis 70º from north.

• The third ellipse has a semimajor axis of 5º and a semiminor axis of 3º. Rotate the semimajor axis 90º from north.

lat0 = 45.5152;
lon0 = -122.6784;
semimajor = [4 4.5 5];
ecc = axes2ecc(semimajor,[2 2.5 3]);
[lat,lon] = ellipse1(lat0,lon0,[semimajor' ecc'],[50 70 90]');

Display the ellipses on a map using thick lines. Differentiate the ellipses by including the semimajor axes in a legend.

geobasemap streets
hold on
for i=1:size(lat,2)
    geoplot(lat(:,i),lon(:,i),LineWidth=2,DisplayName=string(semimajor(i))+char(176))
end
legend

Multiple Ellipses with Different Centers

Find the coordinates of three ellipses with different centers.

• Center the first ellipse on Boston. Specify the semimajor axis as 4º and the semiminor axis as 2º. Rotate the semimajor axis 50º from north.

• Center the second ellipse on New York City. Specify the semimajor axis as 4.5º and the semiminor axis as 2.5º. Rotate the semimajor axis 120º from north.

• Center the third ellipse on Chicago. Specify the semimajor axis as 5º and the semiminor axis as 3º. Rotate the semimajor axis 90º from north.

lat0 = [42.3601 40.7128 41.8781]';
lon0 = [-71.0589 -74.0060 -87.6298]';
cities = ["Boston" "New York City" "Chicago"];
semimajor = [4 4.5 5];
ecc = axes2ecc(semimajor,[2 2.5 3]);
[lat,lon] = ellipse1(lat0,lon0,[semimajor' ecc'],[50 120 90]');

Display the ellipses on a map using thick lines. Differentiate the ellipses by including the city names in a legend.

figure
geobasemap streets
hold on
for i=1:size(lat,2)
    geoplot(lat(:,i),lon(:,i),LineWidth=2,DisplayName=cities(i))
end
legend

Input Arguments

lat0 — Latitude of center of ellipse

scalar | column vector

Latitude of the center of the ellipse, specified as a scalar or a column vector.

• To find the coordinates of multiple ellipses with the same center, specify lat0 and lon0 as scalars and specify ellipse as a two-column matrix. The number of rows in the matrix is the number of ellipses.

• To find the coordinates of multiple ellipses with different centers, specify lat0 and lon0 as column vectors and specify ellipse as a two-column matrix. The number of elements in lat0 and lon0 must match the number of rows in ellipse.

The sizes of lat0 and lon0 must match.

Data Types: double

lon0 — Longitude of center of ellipse

scalar | column vector

Longitude of the center of the ellipse, specified as a scalar or a column vector.

• To find the coordinates of multiple ellipses with the same center, specify lat0 and lon0 as scalars and specify ellipse as a two-column matrix. The number of rows in the matrix is the number of ellipses.

• To find the coordinates of multiple ellipses with different centers, specify lat0 and lon0 as column vectors and specify ellipse as a two-column matrix. The number of elements in lat0 and lon0 must match the number of rows in ellipse.

The sizes of lat0 and lon0 must match.

Data Types: single | double

ellipse — Ellipse

two-column matrix

Ellipse, specified as a two-column matrix. Each row of the matrix defines an ellipse and has the form [semimajor_axis eccentricity], where semimajor_axis is the length of the semimajor axis and eccentricity is the eccentricity.

When lat0 and lon0 are column vectors, the number of rows in ellipse must match the number of elements in lat0 and lon0.

Data Types: single | double

offset — Azimuth offset of semimajor axis

[] (default) | scalar | column vector

Azimuth offset of the semimajor axis, specified as a scalar or a column vector. Azimuths are measured clockwise from north. The default value of [] indicates that the semimajor axis goes from north to south.

Unless offset is [], the size of offset must match the number of ellipses.

Data Types: single | double

az — Azimuth indicating section of ellipse to find

[] (default) | column vector | two-column matrix

Azimuth indicating the section of the ellipse to find, specified as one of these options:

• A column vector — Find coordinates of the ellipse from north to the specified azimuth. Each element of az corresponds to a row of ellipse. The size of az must match the number of ellipses.

• A two-column matrix — Find coordinates of the ellipse between the azimuth in the first column and the azimuth in the second column. Each row of az corresponds to a row of ellipse. The number of rows in az must match the number of ellipses.

Azimuths are measured clockwise from north.

The default value of [] specifies a full ellipse.

Data Types: single | double

ellipsoid — Reference ellipsoid

[1 0] (default) | referenceSphere object | referenceEllipsoid object | oblateSpheroid object | two-element numeric vector

Reference ellipsoid, specified as a referenceSphere object, a referenceEllipsoid object, an oblateSpheroid object, or a two-element numeric vector of the form [semimajor_axis eccentricity], where semimajor_axis is the length of the semimajor axis and eccentricity is the eccentricity. The values semimajor_axis and eccentricity must be of data type double.

The default value of [1 0] represents the unit sphere.

units — Angle unit

"degrees" (default) | "radians"

Angle unit, specified as one of these options:

• "degrees" — Degrees

• "radians" — Radians

If you do not specify a reference ellipsoid, this argument determines the angle units for the coordinates, offset, az, and the semimajor axis of ellipse. If you specify a reference ellipsoid, this argument determines the angle units for only the coordinates, offset, and az.

Data Types: char | string

npts — Number of points

100 (default) | scalar

Number of points to include in the ellipse, specified as a scalar. If you specify more than one ellipse, then the function finds npts points per ellipse.

Data Types: single | double

method — Type of distance from center of ellipse

"gc" (default) | "rh"

Type of distance from the center of the ellipse, specified as one of these options:

• "gc" — Use the great circle distance.

• "rh" — Use the rhumb line distance.

Data Types: char | string

Output Arguments

lat — Latitude coordinates of ellipse

column vector | matrix

Latitude coordinates of the ellipse, returned as a column vector with npts elements or a matrix of size npts-by-m, where m is the number of ellipses.

lon — Longitude coordinates of ellipse

column vector | matrix

Longitude coordinates of the ellipse, returned as a column vector with npts elements or a matrix of size npts-by-m, where m is the number of ellipses.

mat — Latitude and longitude coordinates of ellipse

matrix

Latitude and longitude coordinates of the ellipse, returned as a matrix equivalent to [lat lon].

Version History

Introduced before R2006a