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    <p>So I wrote my own function GetLineFromEndPts() that should solve this problem in a kludgy way. Given two points a and b, this function outputs a list of points on a line connecting a and b. Therefore, to find a contour with many points from a polygon defined by a few vertices, I can run this function on consecutive pairs of vertices.</p> <pre><code> /* * 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, &amp;writer ); int t; float tempPtx; float tempPty; int signx=1; int signy=1; for (t = 0; t &lt; (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's sign to round correctly **/ if (tempPtx&lt;0) { signx=-1; } else { signx=1; } if (tempPty&lt;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 &amp;&amp; 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( &amp;writer ); return 1; } </code></pre> <p>And associated functions:</p> <pre><code>/* * 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) ) ); } </code></pre> <p>And finally:</p> <pre><code>/* * 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)) ); } </code></pre> <p>So, for example, if called with: </p> <pre><code>GetLineFromEndPts(cvPoint(0,0),cvPoint(10,15),test); </code></pre> <p>the function outputs:</p> <pre><code> 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 </code></pre>
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