Polygon for contour in OpenCV? for example the opposite of cvApproxPoly ()?

Question

Is there a simple and quick OpenCV solution that converts a set of CvPoint vertices defining a polygon into a path with many other vertices?

I have simple polygons in one space, and I want to convert the polygons to another space where the straight lines will become enticing. Therefore, it is important to add more vertices to my straight lines. It will be the opposite cvApproxPoly().

Internally cvPolyLine()does exactly what I want. Is there any way to access this?

I am using OpenCV 1.1.

Answer 1

, GetLineFromEndPts(), . a b, , a b. , , , .

 /*
 * Given two points a and b , and a sequence of CvPoints
 * this function will find the points that walk the line
 * between a and b and append those
 * the end of the sequence
 *
 * Note that the output  includes point a, but not point b.
 */
int GetLineFromEndPts(CvPoint a, CvPoint b, CvSeq* contour){
    if (contour==NULL) {
        printf("ERROR! contour in GetLineFromEndPts() is NULL!\n");
        return -1;
    }
    float d=dist(a,b);
    /** Normalized vector with components i and j pointing along the line**/
    float ihat= ( (float) (b.x -a.x) ) /d;
    float jhat= ( (float) (b.y -a.y) ) /d;

    CvPoint currPt; /* Current Point On integer grid*/
    CvPoint prevPt=a; /* Prev Point on integer grid */
    currPt=a;

    /** Prepare Writer for Appending Points to Seq **/
    CvSeqWriter writer;
    cvStartAppendToSeq( contour, &writer ); 

    int t;
    float tempPtx;
    float tempPty;
    int signx=1;
    int signy=1;

    for (t = 0; t <  (int) (d+0.5) ; ++t) {

        /** Our target point is now defined by a parametric equation **/
        tempPtx=(float) t * ihat + (float) a.x;
        tempPty=(float) t * jhat + (float) a.y;

        /** We will want to round and we need to know the number sign to round correctly **/
        if (tempPtx<0) {
            signx=-1;
        } else {
            signx=1;
        }
        if (tempPty<0) {
            signy=-1;
        } else{
            signy=1;
        }


        /** Round to an integer value. Note that we need the sign before we add/subtract .5 **/
        currPt=cvPoint((int) ( tempPtx + (float) signx * 0.5 ) ,
                    (int) ( tempPty + (float) signy * 0.5 ));


        /** If first point, OR the current approx point is not the same as prev **/
        if ( t==0 ||  !( currPt.x == prevPt.x && currPt.y == prevPt.y   )   ){

            /** Write out the point **/
            CV_WRITE_SEQ_ELEM( currPt, writer );

        printf(" t=%d\n",t);
        printf(" currPt.x=%d\n",currPt.x);
        printf(" currPt.y=%d\n",currPt.y);


        }
        prevPt=currPt;
    }
    cvEndWriteSeq( &writer );
    return 1;
}

:

/*
 * Returns the squared distance between two points
 */
int sqDist(CvPoint pta, CvPoint ptb){
    return (  ((pta.x - ptb.x)*(pta.x - ptb.x) ) + ((pta.y - ptb.y)*(pta.y - ptb.y)  ) );
}

:

/*
 * Finds the distance between two points
 * and returns the value as a float
 */
float dist(CvPoint a, CvPoint b){
    return ( sqrt( (float) sqDist(a,b))  );
}

, , :

GetLineFromEndPts(cvPoint(0,0),cvPoint(10,15),test);

:

 t=0
 currPt.x=0
 currPt.y=0
 t=1
 currPt.x=1
 currPt.y=1
 t=2
 currPt.x=1
 currPt.y=2
 t=3
 currPt.x=2
 currPt.y=2
 t=4
 currPt.x=2
 currPt.y=3
 t=5
 currPt.x=3
 currPt.y=4
 t=6
 currPt.x=3
 currPt.y=5
 t=7
 currPt.x=4
 currPt.y=6
 t=8
 currPt.x=4
 currPt.y=7
 t=9
 currPt.x=5
 currPt.y=7
 t=10
 currPt.x=6
 currPt.y=8
 t=11
 currPt.x=6
 currPt.y=9
 t=12
 currPt.x=7
 currPt.y=10
 t=13
 currPt.x=7
 currPt.y=11
 t=14
 currPt.x=8
 currPt.y=12
 t=16
 currPt.x=9
 currPt.y=13
 t=17
 currPt.x=9
 currPt.y=14