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PO"no matching function for call to min_element" when using a vector of CvPoints (opencv)
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  1. PO"no matching function for call to min_element" when using a vector of CvPoints (opencv)
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    copied!<p>Here's my function to retrieve the corners of a rectangle, the input is a thresholded image (with a numberplate on it) and I want the output to be a vector (within a vector) with the cornerpoints of the plate. Ordered: left_up, right_up, right_bottom, left_bottom.</p> <p>I use openCV to find the contours (which works fine); after some filters, I use approxPoly to find rectangles. I find four points, which is great, but I want to order them. I thought the following would work: put all the point in a vector</p> <p>find min_element specified by compare function Left and erase from vector</p> <p>find another left element and erase, then determine which is up and which is down.</p> <p>the remaining two points are the right points.</p> <pre><code>bool left(CvPoint &amp;pt1, CvPoint &amp;pt2) { return pt1.x &lt; pt2.x; } bool up(CvPoint &amp;pt1, CvPoint &amp;pt2) { return pt1.y &lt; pt2.y; } std::vector&lt;std::vector&lt;CvPoint&gt; &gt; findNumberPlate(IplImage* img) { vector&lt;CvPoint&gt; numberplate; vector&lt;vector&lt;CvPoint&gt; &gt; numberplates_output; CvMemStorage* storage = cvCreateMemStorage(0); CvMemStorage* storage2 = cvCreateMemStorage(0); CvSeq* contour = 0; cvFindContours(img, storage, &amp;contour, sizeof (CvContour), CV_RETR_EXTERNAL); CvSeq* result = 0; for (CvSeq* c = contour; c != NULL; c = c-&gt;h_next) { double area_contour = cvContourArea(c, CV_WHOLE_SEQ); CvBox2D c_box = cvMinAreaRect2(c); double area_box = c_box.size.height * c_box.size.width; if (area_contour / area_box &gt; 0.83 &amp;&amp; area_contour &gt; 2000) { if (!storage2 == 0) cvClearMemStorage(storage2); else storage2 = cvCreateMemStorage(0); result = cvApproxPoly(c, sizeof (CvContour), storage2, CV_POLY_APPROX_DP, cvContourPerimeter(c)*0.03, 0); if (result-&gt;total == 4) { //find up/bottom &amp; left/right vector&lt;CvPoint&gt; points; for (int i = 0; i &lt; 4; i++) { CvPoint* tempPoint = (CvPoint*) cvGetSeqElem(result, i); points.push_back(cvPoint(tempPoint-&gt;x,tempPoint-&gt;y)); } vector&lt;CvPoint&gt;::iterator itLeft1 = std::min_element(points.begin(), points.end(), left); points.erase(itLeft1); vector&lt;CvPoint&gt;::iterator itLeft2 = std::min_element(points.begin(), points.end(), left); points.erase(itLeft2); vector&lt;CvPoint&gt;::iterator itLeftUp = std::min(itLeft1, itLeft2, left); vector&lt;CvPoint&gt;::iterator itLeftBottom = std::max(itLeft1, itLeft2, left); CvPoint left_up = *itLeftUp; CvPoint left_bottom = *itLeftBottom; vector&lt;CvPoint&gt;::iterator itRightUp = std::min(points.begin(), points.end(), up); vector&lt;CvPoint&gt;::iterator itRightBottom = std::max(points.begin(), points.end(), up); CvPoint right_up = *itRightUp; CvPoint right_bottom = *itRightBottom; //etc } </code></pre> <p>However, when using the function min_element &amp; max_element I get several errors I don't understand. </p> <pre><code>findNumberPlate.cpp:57: error: no matching function for call to ‘min_element(__gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;, __gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;, &lt;unresolved overloaded function type&gt;)’ findNumberPlate.cpp:59: error: no matching function for call to ‘min_element(__gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;, __gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;, &lt;unresolved overloaded function type&gt;)’ findNumberPlate.cpp:62: error: no matching function for call to ‘min(__gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;&amp;, __gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;&amp;, &lt;unresolved overloaded function type&gt;)’ findNumberPlate.cpp:63: error: no matching function for call to ‘max(__gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;&amp;, __gnu_cxx::__normal_iterator&lt;CvPoint*, std::vector&lt;CvPoint, std::allocator&lt;CvPoint&gt; &gt; &gt;&amp;, &lt;unresolved overloaded function type&gt;)’ </code></pre> <p>Can't I use CvPoints with min_element? Or... Can anyone help me? </p> <p>Thanks!</p>
 

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