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Krispijn Scholte

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Royal Netherlands Navy

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Lieutenant in the Royal Netherlands Navy, currently working at CAMS-Force Vision writing operational software for combat ships.

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27 Jan 2009 Screenshot Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte computational geometr..., computational, enlarge, polygon, geometry, extension 19 13
  • 5.0
5.0 | 7 ratings
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28 Jan 2009 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte

Thank you for the feedback. As it turns out, there was a bug in the selfintersection algorithm that I used. This lead to the "V"-polygon being identified as having selfintersections. I have replaced it with a newer, vectorbased one that seems to yield better results.

I have also added the (optional) "resolution"-parameter you requested.

The self-intersecting extended polygon (from the "banana"-poly) still occurs as I have not found out why this happens. When I do, I'll update again.
30 Oct 2008 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte

The algorithm wasn't intended for use with negative ranges. I originally made for plotting weapon ranges from areas a threat is expected which entails only positive ranges.

I've allowed the code to run with negative ranges, as I have observed some results that seemed correct, but it generates a warning as I have not really tested it and it wasn't originally intended to do so.

The NaN scenario has not occured to me (I do not have the mapping toolbox) but I can imagine that it would be possible to modify it in order to run the code on each segment. The code is intended for a single segment.

A work around for this should probably look like something along these lines:
[mcode]
P0 = [rand(3,2);NaN,NaN;rand(3,2)];

%rewrite the segmented polygon to a cell array
segmentCounter = 1;
pointIndexCounter = 1;
for i=1:size(P0,1)
    if ~isnan(P0(i,1))
        P0cell{segmentCounter}(pointIndexCounter,:)=P0(i,:);
        pointIndexCounter = pointIndexCounter + 1;
    else
        segmentCounter = segmentCounter + 1;
        pointIndexCounter = 1;
    end
end

figure(1);hold on; axis equal;

for i=1:length(P0cell)
   
    P1 = extendPoly(P0cell{i}, .1 );
    figure(1); plot(P0cell{i}(:,1),P0cell{i}(:,2),'-o',P1{1}(:,1),P1{1}(:,2),'.r-');
    
end

hold off;
[/mcode]

Might be interesting to include in a next version.
29 Oct 2008 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte

Updated to v1.3: Added warning and error messages as well as automatic polygon closing (generates a warning).

Thanks for taking the time to review the code (first time contributing).

29 Oct 2008 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte

Thank you for your feedback John. Discovered and fixed a small bug in determining if the input polygon is defined CW or CCW.

Please note that your test code should read:
"P1 = extendPoly(rand(3,2) , .1 );" should read "P1 = extendPoly(P0 , .1 );" Because otherwise the extended polygon will always be different from the input.
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28 Jan 2009 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte Andres

I hope the self-intersecting extension issue can be fixed. Note that in the center of the V-poly extension there seem to be two identical points in the extended polygon (I just stepped through with a datatip + arrow keys).

But above all, thanks for your fast support!
28 Jan 2009 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte Scholte, Krispijn

Thank you for the feedback. As it turns out, there was a bug in the selfintersection algorithm that I used. This lead to the "V"-polygon being identified as having selfintersections. I have replaced it with a newer, vectorbased one that seems to yield better results.

I have also added the (optional) "resolution"-parameter you requested.

The self-intersecting extended polygon (from the "banana"-poly) still occurs as I have not found out why this happens. When I do, I'll update again.
26 Jan 2009 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte Andres

Thanks for sharing this! The polygon extension is a most desirable function - but I think there is some unexpected behaviour with your code. I've tested some polygons with your help code

extendedPolygon = extendPoly(Polygon,0.4);
figure(1); clf; patch(Polygon(:,1),Polygon(:,2),'r');
for i=1:length(extendedPolygon)
 toPlot=extendedPolygon{i};
 line(toPlot(:,1),toPlot(:,2),'Color','b');
end

1) The v-like polygon

Polygon = [0,0;1,1;1,2;0,1.00;-1,2;-1,1;0,0];

produces an self-intersection error, while the very similar

Polygon = [0,0;1,1;1,2;0,0.90;-1,2;-1,1;0,0];

does not.

2) Some banana-like (non-convex) polygons like

xt = (1:5).';
yt = log(xt);
Polygon = [[xt;flipud(xt) ;xt(1)],...
          [ yt;flipud(yt)-1;yt(1)]];

produce a self-intersecting extended polygon, see the detail

xlim([4,4.2])
ylim([-0.02,0.02])

Plus: It would be nice to have control over the resolution of the circular sections of the extended polygon.
13 Jan 2009 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte van Norden, Wilbert

Function does exactly what I expected, in my case expending freely drawn areas (polygons) by a given weapon range or sensor range.
Although it first glance the problem seemed simple, it is somewhat complex so thanks for posting this!!
10 Nov 2008 Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte Kearney, Kelly

The Nov 10 update fixes the bug I was seeing that generated empty results; the extended polygons created for my test polygons look good now. This function is still slower than bufferm.m (by about a factor of 10), but has the very nice advantage of not requiring the Mapping Toolbox. Thanks to the author for the quick response to comments.
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27 Jan 2009 Screenshot Accurate polygon extension Enlarges polygon by a specified range. Also generates internal polygons caused by intersections. Author: Krispijn Scholte computational geometr..., computational, enlarge, polygon, geometry, extension 19 13
  • 5.0
5.0 | 7 ratings
 

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