source: issm/trunk-jpl/src/m/shp/shpcoarsen.m

function shpcoarsen(newfile,oldfile,resolution)
%SHPCOARSEN - coarsen an shp polygon
%
%   This routine reads a polygon shapefile and remove points with respect to
%   the resolution (in meters) given in input. 
%
%   Usage:
%      shpcoarsen(newfile,oldfile,resolution)
%
%   Example:
%       shpcoarsen('DomainOutline.shp','Antarctica.shp',4000)

%Some checks
if nargin~=3 | nargout
        error('shpcoarsen usage: shpcoarsen(newfile,oldfile,resolution)')
elseif ~exist(oldfile)
        error(['shpcoarsen error message: the file ' oldfile ' does not exist'])
elseif exist(newfile),
        %choice=input(['A file ' newfile ' already exists, do you want to modify it? (y/n)'],'s');
        %if ~strcmpi(choice,'y'),
        %       disp('no modification done ... exiting');
        %       return;
        %end
end

%Get oldfile: 
A=shpread(oldfile);
numprofiles=size(A,2);

%Go through the profiles
count=1;
while count<=numprofiles,

        %get number of points and initialize j
        numpoints=length(A(count).x);
        j=1;

        %stop if we have reached end of profile (always keep the last point)
        while j<numpoints,

                %See whether we keep this point or not
                distance=sqrt((A(count).x(j)-A(count).x(j+1))^2+(A(count).y(j)-A(count).y(j+1))^2);
                if distance<resolution & j<numpoints-1  %do not remove last point
                        A(count).x(j+1)=[];
                        A(count).y(j+1)=[];
                        numpoints=numpoints-1;
                else
                        division=floor(distance/resolution)+1;
                        if division>=2,
                                x=linspace(A(count).x(j),A(count).x(j+1),division)';
                                y=linspace(A(count).y(j),A(count).y(j+1),division)';
                                A(count).x=[A(count).x(1:j);x(2:end-1); A(count).x(j+1:end)];
                                A(count).y=[A(count).y(1:j);y(2:end-1); A(count).y(j+1:end)];

                                %update current point
                                j=j+1+division-2;
                                numpoints=numpoints+division-2;
                        else
                                %update current point
                                j=j+1;
                        end
                end
        end
        if length(A(count).x)<=1,
                A(count)=[];
                numprofiles=numprofiles-1;
        else
                count=count+1;
        end
end

%write output
shpwrite(A,newfile);