bufferm

Buffer zones for latitude-longitude polygons

Syntax

[latb,lonb] = bufferm(lat,lon,bufwidth)
[latb,lonb] = bufferm(lat,lon,bufwidth,direction)
[latb,lonb] = bufferm(lat,lon,bufwidth,direction,npts)

Description

[latb,lonb] = bufferm(lat,lon,bufwidth) computes the buffer zone around a line or polygon. If the vectors lat and lon, in units of degrees, define a line, then latb and lonb define a polygon that contains all the points that fall within a certain distance, bufwidth, of the line. bufwidth is a scalar specified in degrees of arc along the surface. If the vectors lat and lon define a polygon, then latb and lonb define a region that contains all the points exterior to the polygon that fall within bufwidth of the polygon.

[latb,lonb] = bufferm(lat,lon,bufwidth,direction) where direction specifies whether the buffer zone is inside ('in') or outside ('out') of the polygon. A third option, 'outPlusInterior', returns the union of an exterior buffer (as would be computed using 'out') with the interior of the polygon. If you do not supply a direction value, bufferm uses 'out' as the default and returns a buffer zone outside the polygon. If you supply 'in' as the direction value, bufferm returns a buffer zone inside the polygon. If you are finding the buffer zone around a line, 'out' is the only valid option.

[latb,lonb] = bufferm(lat,lon,bufwidth,direction,npts) controls the number of points used to construct circles about the vertices of the polygon. A larger number of points produces smoother buffers, but requires more time. If npts is omitted, 13 points per circle are used.

Examples

collapse all

Display a simplified version of the five polygons that represent the Great Lakes.

tol = 0.05;
[latr, lonr] = reducem(gtlakelat, gtlakelon, tol);
figure('Color','w')
ax = usamap({'MN','NY'});
setm(ax,'MLabelLocation',5)
geoshow(latr, lonr, 'DisplayType', 'polygon', ...
'FaceColor', 'blue')
title('Great Lakes')

Set the buffer width and display a buffer zone outside the lakes.

figure;
bufwidth = 1;
[latb, lonb] = bufferm(latr, lonr, bufwidth);
geoshow(latb, lonb, 'DisplayType', 'polygon', ...
'FaceColor', 'yellow')
title('Exterior Buffer Zone')

Display a buffer zone inside the polygon.

figure;
[lati, loni] = bufferm(latr, lonr, 0.3*bufwidth, 'in');
geoshow(lati, loni, 'DisplayType', 'polygon', ...
'FaceColor', 'magenta')
title('Interior Buffer Zone')

Display the Great Lakes with interior and exterior buffer zones on a backdrop of neighboring states.

figure('Color','w')
ax = usamap({'MN','NY'});
setm(ax,'MLabelLocation',5)
geoshow(latb, lonb, 'DisplayType', 'polygon', 'FaceColor', 'yellow')
geoshow(latr, lonr, 'DisplayType', 'polygon', 'FaceColor', 'blue')
geoshow(lati, loni, 'DisplayType', 'polygon', 'FaceColor', 'magenta')
geoshow(uslat, uslon)
geoshow(statelat, statelon)
title('Great Lakes and Buffer Zones with Neighboring States')

Use the 'outPlusInterior' option.

bufWidth = 0.5;
[latz, lonz] = bufferm(latr, lonr, bufWidth,'outPlusInterior');
figure
geoshow(latz,lonz,'DisplayType','polygon','FaceColor','yellow')
title('Exterior Buffer Zone including Polygon Interior');

Tips

Close all polygons before processing them with bufferm. If a polygon is not closed, bufferm assumes it is a line.