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
Use the bufferm function to generate a buffer zone internal to a land area polygon.
Import Madagascar polygon shape.
madagascar = shaperead('landareas.shp','UseGeoCoords',true, ... 'Selector', {@(name)strcmpi(name,'Madagascar'),'Name'});
Create a map showing Madagascar.
figure
worldmap('madagascar')
geoshow(madagascar)
Use bufferm to create a buffer zone that extends 0.75 degrees inland from the coast of Madagascar.
madlat = madagascar.Lat;
madlon = madagascar.Lon;
bufwidth = 0.75;
direction = 'in';
[latbuf,lonbuf] = bufferm(madlat,madlon,bufwidth,direction);Show the buffer zone in green.
geoshow(latbuf,lonbuf,'DisplayType','polygon','FaceColor','green')
Display a simplified version of the five polygons that represent the Great Lakes.
load conus 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.
