The Orientation Angle Detection of Multiple Insulators in Aerial Image - Advances in Image and Graphics Technologies - page 299

2.3 The Determination of Main Direction of Insulator

All the candidate points can be extracted including some error points, and the accurate
points can be picked up by RANSAC, and the straight line which points locate in is
the main direction orientation of insulator shown in Fig. 7.

(a) (b)

Fig. 7. The detected orientation angles of insulator. (a) Main direction of insulator. (b) Rotated
insulator.

3 Experimental Results

3.1 The Results of Angles Detection of Multiple Insulators

The results of angles detection of multiple insulators are as following:
Fig. 8(a) is an image with two insulators (Im 2), and (b) is its binary image after
preprocessing. It can be seen that the edges of binary image become smoothness and
clearness which simplifies the computation and increases the accuracy.
Extract the contours of Im 2 shown in Fig. 9(a), and link edge pixels together into
lists of sequential edge points for every contour of Im 2. Reserve the contours which
are longer than definite value.
For each contour, the steps of the detection of orientation angle are as following:
Shown in Fig. 9(b), the contour of binary image which is concave-Convex and ir-
regular curve after preprocessing is approximated by a large number of line segments
with specified tolerance, and each color represents a connected contour composed by
straight line segments. Thus the points in each contour can be formed as a list of con-
nected edge points.
Compute the orientation angle for each point in each list, and all the angles are
composed of a set of sequential angular variation. The points with sign-Changing
angle would be extracted as candidate points. If the number of candidate points of the
contour is too less, the contour can be ignored as pseudo-insulator. Fig. 10 shows
candidate points of each connected contour in Im 2.
All the candidate points can be extracted including some error points, and the accu-
rate points can be picked up by RANSAC, and the straight line which points locate in
is the main direction of insulator.
After iterations, the orientation angles of all the connected contours can be detected
finally. Fig. 11 is the results of orientation angle detection of all insulators.