Detection

IMAGE PREPROCESSING

The images from the camera was first converted to HSV color space and a thresholding algorithm is applied to obtain only the pixels of a certain color. The thresholding algorithm is an important part of the image preprocessing step as it avoids unwanted parts of the images(shadow of the quadcopter). Further the contours of image are extracted and is processed as described below.

PLATFORM DETECTION

The convex hulls of the contours are extracted and the size of each hull is compared with a threshold value(this depends on height because the hull size became smaller as height increases). The hulls which has size greater than the threshold value is passed through a function which returns the near approximated polygon of the hulls(choosing an error limit to this function is also an important task of this section). The hulls are considered valid and thus the platform is said to be detected if the polygon is a quadrilateral(the platform used is nearly quadrilateral).