Documentation

scircle2

Small circles from center and perimeter

Syntax

[lat,lon] = scircle2(lat1,lon1,lat2,lon2)
[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid)
[lat,lon] = scircle2(lat1,lon1,lat2,lon2,units)
[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid,units)
[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid,units,npts)
[lat,lon] = scircle2(track,...)
mat = scircle2(...)
mat = [lat lon]

Description

[lat,lon] = scircle2(lat1,lon1,lat2,lon2) computes small circles (on a sphere) with centers at the points lat1,lon1 and points on the circles at lat2,lon2. The inputs can be scalar or column vectors.

[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid) computes the small circle on the ellipsoid defined by the input ellipsoid, rather than by assuming a sphere. ellipsoid is a referenceSphere, referenceEllipsoid, or oblateSpheroid object, or a vector of the form [semimajor_axis eccentricity]. Default is a unit sphere.

[lat,lon] = scircle2(lat1,lon1,lat2,lon2,units) and
[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid,units) are valid calling forms, which use the input units to define the angle units of the inputs and outputs. If you omit units, 'degrees' is assumed.

[lat,lon] = scircle2(lat1,lon1,lat2,lon2,ellipsoid,units,npts) uses the scalar input npts to determine the number of points per track computed. The default value of npts is 100.

[lat,lon] = scircle2(track,...) uses track to define either a great circle or a rhumb line radius. If track' = 'gc', then small circles are computed. If track = 'rh', then circles with radii of constant rhumb line distance are computed. If you omit track, 'gc' is assumed.

mat = scircle2(...) returns a single output argument where mat = [lat lon]. This is useful if a single circle is computed.

Multiple circles can be defined from a single center point by providing scalar lat1,lon1 inputs and column vectors for the points on the circumference, lat2,lon2.

Examples

collapse all

Plot the locus of all points the same distance from New Delhi as Kathmandu.

axesm('mercator','MapLatlimit',[0 40],'MapLonLimit',[60 110]);
% For reference
plotm(coastlat,coastlon,'k');
% New Delhi
lat1 = 29; lon1 = 77.5;
% Kathmandu
lat2 = 27.6; lon2 = 85.5;
% Plot the cities
plotm([lat1 lat2],[lon1 lon2],'b*')
[latc,lonc] = scircle2(lat1,lon1,lat2,lon2);
plotm(latc,lonc,'b') collapse all

Small Circle

A small circle is the locus of all points an equal surface distance from a given center. For true small circles, this distance is always calculated in a great circle sense. However, the scircle2 function allows a locus to be calculated using distances in a rhumb line sense as well. An example of a small circle is all points exactly 100 miles from the Washington Monument. 