added comment

gtsam/geometry/CameraSet.h

@@ -57,7 +57,7 @@ protected:
     Vector b(ZDim * m);
     for (size_t i = 0, row = 0; i < m; i++, row += ZDim) {
       Vector bi = traits<Z>::Local(measured[i], predicted[i]);
-      if(ZDim==3 && std::isnan(bi(1))){ // compensate for the case in which the right pixel in a stereoPoint is missing (nan)
+      if(ZDim==3 && std::isnan(bi(1))){ // if it is a stereo point and the right pixel is missing (nan)
         bi(1) = 0;
       }
       b.segment<ZDim>(row) = bi;