Visualize checkerboard points

[sourishg]

For every stereo pair visualize the checkboard points detected using imshow. Ideally, this visualization should be triggered by a command-line flag argument.

[blazczak]

This is easily done with cv::findChessboardCorners() and cv::drawChessboardCorners() from calib3d. The detectAndParseChessboard() routine in opencv_interactive-calibration does this already - simply as a wrapper over those two functions - and can be used verbatim. In addition, the output of the wrapper can be used to determine if you have a parse-able image of the chessboard in both channels before making them candidates for saving, increasing the quality of input data for the subsequent calibration stages.

direct patch as a starting point:

index 5279fee..fefac40 100644
--- read_images.cpp
+++ read_images.cpp
@@ -1,3 +1,4 @@
+#include <opencv2/calib3d.hpp>
 #include <opencv2/core/core.hpp>
 #include <opencv2/highgui/highgui.hpp>
 #include <opencv2/imgproc/imgproc.hpp>
@@ -9,6 +10,25 @@ using namespace std;
 using namespace cv;
 
 int x = 0;
+Size mBoardSize = Size(7, 10);
+std::vector<cv::Point2f> mCurrentImagePoints;
+std::vector<cv::Point2f> mTemplateLocations;
+
+bool detectAndParseChessboard(const cv::Mat &frame)
+{
+    int chessBoardFlags = cv::CALIB_CB_ADAPTIVE_THRESH | cv::CALIB_CB_NORMALIZE_IMAGE | cv::CALIB_CB_FAST_CHECK;
+    bool isTemplateFound = cv::findChessboardCorners(frame, mBoardSize, mCurrentImagePoints, chessBoardFlags);
+
+    if (isTemplateFound) {
+        cv::Mat viewGray;
+        cv::cvtColor(frame, viewGray, cv::COLOR_BGR2GRAY);
+        cv::cornerSubPix(viewGray, mCurrentImagePoints, cv::Size(11,11),
+            cv::Size(-1,-1), cv::TermCriteria( cv::TermCriteria::EPS+cv::TermCriteria::COUNT, 30, 0.1 ));
+        cv::drawChessboardCorners(frame, mBoardSize, cv::Mat(mCurrentImagePoints), isTemplateFound);
+        mTemplateLocations.insert(mTemplateLocations.begin(), mCurrentImagePoints[0]);
+    }
+    return isTemplateFound;
+}
 
 int main(int argc, char const *argv[])
 {
@@ -35,8 +55,12 @@ int main(int argc, char const *argv[])
   while (1) {
     cap1 >> img1;
     cap2 >> img2;
-    resize(img1, img_res1, Size(im_width, im_height));
-    resize(img2, img_res2, Size(im_width, im_height));
+    img_res1 = img1.clone();
+    img_res2 = img2.clone();
+    detectAndParseChessboard(img_res1);
+    detectAndParseChessboard(img_res2);
+    resize(img_res1, img_res1, Size(im_width, im_height));
+    resize(img_res2, img_res2, Size(im_width, im_height));
     imshow("IMG1", img_res1);
     imshow("IMG2", img_res2);
     if (waitKey(30) > 0) {