interpolating polygons

[Tony Shepherd]

Hi,
I've been scrolling through the source code for ages but I can't find a
method that returns a list of pixel co-ordinates for the whole boundary of a
polygon object (not just the vertices)
-- is there one? or has someone written one? (it needs to somehow
interpolate between the vertices)

Many Thanks
T

[jmutterer]

Tony, you can run the following macro code which will convert the
polygon to a freehand type of selection.

roiManager("Combine");
getSelectionCoordinates(x,y);

Jerome


On 9/1/06, Tony <[hidden email]> wrote:

> Hi,
> I've been scrolling through the source code for ages but I can't find a
> method that returns a list of pixel co-ordinates for the whole boundary of a
> polygon object (not just the vertices)
> -- is there one? or has someone written one? (it needs to somehow
> interpolate between the vertices)
>
> Many Thanks
> T
>

[Wayne Rasband]

> I've been scrolling through the source code for ages but I can't
> find a method that returns a list of pixel co-ordinates for the
> whole boundary of a polygon object (not just the vertices)
> -- is there one? or has someone written one? (it needs to
> somehow interpolate between the vertices)

The Path_Writer plugin
(http://rsb.info.nih.gov/ij/plugins/path-writer.html) does this.

-wayne

[Tony Shepherd]

Thanks Wayne, that works a treat.
I've adapted it to create an object containing connected pixel co-ordinates
if anybody wants to use it (below). Note that the constructor needs an roi
object, which could be an ellipse, polygon or whatever.

T


 public class Tboundary {


    int XY[][];
    int n;  

   // A Tboundary is a list of all connected pixels in the ellipse boundary
   // note that the first and last co-ordinate pairs are the same (first    
      pixel revisited)
   

   public Tboundary(Roi roi)
     {

        Polygon temproi = roi.getPolygon();
        PolygonRoi p = new PolygonRoi(temproi,2);

        int n = p.getNCoordinates();
        int[] x = p.getXCoordinates();
        int[] y = p.getYCoordinates();
        Rectangle r = roi.getBoundingRect();
        int xbase = r.x;
        int ybase = r.y;
        boolean areaPath = roi.getType()<=Roi.TRACED_ROI;
        double length = 0.0;
        double segmentLength;
        int xdelta, ydelta, iLength;
        double[] segmentLengths = new double[n];
        int[] dx = new int[n];
        int[] dy = new int[n];
        for (int i=0; i<(n-1); i++) {
            xdelta = x[i+1] - x[i];
            ydelta = y[i+1] - y[i];
            segmentLength = Math.sqrt(xdelta*xdelta+ydelta*ydelta);
            length += segmentLength;
            segmentLengths[i] = segmentLength;
            dx[i] = xdelta;
            dy[i] = ydelta;
        }
        if (areaPath) {
            xdelta = x[0] - x[n-1];
            ydelta = y[0] - y[n-1];
            segmentLength = Math.sqrt(xdelta*xdelta+ydelta*ydelta);
            length += segmentLength;
            segmentLengths[n-1] = segmentLength;
            dx[n-1] = xdelta;
            dy[n-1] = ydelta;
       }

        int size = (int)(1.1*length);
        int arrayLength = size;
        int[][] xypath = new int[2][size];
        int pathLength = 0;
        double leftOver = 1.0;
        double distance = 0.0;
        int index = -1;
        for (int i=0; i<n; i++) {
            double len = segmentLengths[i];
            if (len==0.0)
                continue;
            double xinc = dx[i]/len;
            double yinc = dy[i]/len;
            double start = 1.0-leftOver;
            double rx = xbase+x[i]+start*xinc;
            double ry = ybase+y[i]+start*yinc;
            double len2 = len - start;
            int n2 = (int)len2;
            for (int j=0; j<=n2; j++) {
                index++;
                if (index<xypath[0].length) {
                    xypath[0][index] = (int)Math.round(rx);
                    xypath[1][index] = (int)Math.round(ry);
                    pathLength = index+1;
                }
                rx += xinc;
                ry += yinc;
            }
            distance += len;
            leftOver = len2 - n2;
        }

        this.XY = xypath;
        this.n = pathLength;

     }

[Tony Shepherd]

didn't make that so clear did I.
The point is, you need to set the integer in

PolygonRoi p = new PolygonRoi(temproi,2);

(i.e. 2 above) to match the Roi TYPE you're dealing with. (2=ellipse,
1=polygon etc).