Sun position tracking method based on black sun effect of image sensor, computer program stored in medium, and solar sensor using the same

• US 10,373,321 B2
• Filed: 05/01/2017
• Issued: 08/06/2019
• Est. Priority Date: 05/03/2016
• Status: Active Grant

• Current Assignee: SungKyunKwan University's Research & Business Foundation (SungKyunKwan University (SKKU))
• Original Assignee: SungKyunKwan University's Research & Business Foundation (SungKyunKwan University (SKKU))
• Inventors: Lee, Sukhan, Saleem, Rashid, Kim, Jaewoong
• Primary Examiner(s): Fujita, Katrina R
• Application Number:
  US15/583,486
• Publication Number:
  US 20170323453A1
• Time in Patent Office: 827 Days
• CPC Class Codes: G06T 2207/20221 Image fusion; Image merging
• CPC Class Codes: G06T 2207/30181 Earth observation
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 7/136 involving thresholding
• CPC Class Codes: G06T 7/246 using feature-based methods, e.g. the tracking of corners or segments
• CPC Class Codes: G06T 7/248 involving reference images or patches
• CPC Class Codes: G06T 7/277 involving stochastic approaches, e.g. using Kalman filters
• CPC Class Codes: G06T 7/292 Multi-camera tracking
• CPC Class Codes: H02S 20/32 specially adapted for solar tracking
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

The present invention provides a sun position tracking method based on a black sun effect of an image sensor, a computer program including commands for causing a computer system to perform the method, and a solar sensor using the method. The sun position tracking method includes processing a plurality of images captured using a plurality of image sensors installed to capture a plurality of images of the sun irrespective of the position of the sun to estimate the center point of the black sun and track the position of the sun.

Claims

1. A sun position tracking method, comprising:

capturing at least one image using at least one image sensor;

extracting solar vectors based on at least one location of at least one black spot appearing in the captured at least one image; and

determining a position of a sun based on a rotation involving solar vectors, among the extracted solar vectors, measured at different time points,

wherein the at least one black spot is caused by overexposure of pixels in the at least one image sensor corresponding to the at least one location of the at least one black spot in the at least one captured image.

2. The sun position tracking method according to claim 1, wherein the capturing of the at least one image enables the position of the sun to be tracked.

3. The sun position tracking method according to claim 1, wherein a plurality of sun position estimation results is fused based on the captured at least one image to track the position of the sun.

4. The sun position tracking method according to claim 1, further comprising estimating a center point of each black spot of the at least one black spot in the captured at least one image,

wherein the extracting of the solar vectors comprises extracting the solar vectors with respect to the center point of each black spot of the at least one black spot, and

wherein the determining of the position of the sun comprises transforming the extracted solar vectors into reference coordinates, and fusing the transformed solar vectors.

5. The sun position tracking method according to claim 4, wherein the estimating of the center point of each black spot of the at least one black spot comprises

acquiring an image of the sun from among the captured at least one image,

repeatedly segmenting the image of the sun while varying an intensity threshold value,

detecting corner points, in response to the image of the sun being segmented, and

obtaining the center point from the detected corner points at a final segmenting of the image of the sun.

6. The sun position tracking method according to claim 5, wherein

the obtaining of the center point comprises obtaining a centroid of strong corner points corresponding to corner points detected from the final segmented image of the sun, and

the estimating of the center point further comprises estimating a strong corner point, among the strong corner points, having a minimum distance from the centroid, as the center point.

7. The sun position tracking method according to claim 4, wherein the transforming of the extracted solar vectors into the reference coordinates comprises

obtaining an initial rotation using the solar vectors, among the extracted solar vectors, which are represented in sensor coordinates, and other solar vectors, among the extracted solar vectors, represented in the reference coordinates, at the different time points, and

determining an average of a plurality of initial rotations calculated by changing the different time points by a predetermined number of times as a final rotation, to transform the extracted solar vectors into the reference coordinates.

8. The sun position tracking method according to claim 4, wherein the fusing of the solar vectors comprises

removing noise of azimuths and altitudes of the solar vectors, and

fusing the solar vectors to calculate a final solar vector.

9. The sun position tracking method according to claim 8, wherein the removing of the noise comprises using a Kalman filter to remove the noise.

10. A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform the method of claim 1.

11. The sun position tracking method of claim 1, wherein an intensity of light impinging on the pixels in the at least one image sensor corresponding to the at least one location of the at least one black spot in the captured at least one image is maximal compared to remaining pixels in the at least one image sensor.

12. A solar sensor, comprising:

at least one sensor configured to capture at least one image; and

at least one processor configured to extract solar vectors based on at least one location of at least one black spot appearing in the captured at least one image, and determine a position of a sun based on a rotation involving solar vectors, among the extracted solar vectors, measured at different time points,

wherein the at least one black spot is caused by overexposure of pixels in the at least one image sensor corresponding to the at least one location of the at least one black spot in the captured at least one image.

13. The solar sensor according to claim 12, wherein

the captured at least one image enables the position of the sun to be tracked, and

the at least one processor is further configured to fuse a plurality of sun position estimation results based on the captured at least one image to track the position of the sun.

14. The solar sensor according to claim 12, wherein the at least one processor comprises

a center point estimation module configured to estimate a center point of each black spot of the at least one black spot in the captured at least one image,

a solar vector extraction module configured to extract the solar vectors with respect to the center point,

a coordinate transformation module configured to transform the extracted solar vectors into reference coordinates, and

a fusion module configured to fuse the transformed solar vectors.

15. The solar sensor according to claim 14, wherein the center point estimation module is further configured to

acquire an image of the sun from among the captured at least one image,

repeatedly segment the image of the sun by a predefined number of times while varying an intensity threshold value,

detect corner points, in response to the image of the sun being segmented,

obtain a centroid of strong corner points corresponding to corner points, among the corner points, detected from a final segmented image, and

estimate a strong corner point, among the corner points, having a minimum distance from the centroid as the center point.

16. The solar sensor according to claim 14, wherein the coordinate transformation module is further configured to

obtain an initial rotation using the solar vectors, among the extracted solar vectors, which are represented in sensor coordinates, and other solar vectors, among the extracted solar vectors, represented in the reference coordinates, at the different time points, and

determine an average of a plurality of initial rotations calculated by changing the different time points by a predetermined number of times as a final rotation, to transform the extracted solar vectors into the reference coordinates.

17. The solar sensor according to claim 14, wherein the fusion module is further configured to remove noise of azimuths and altitudes of the solar vectors, and fuse the solar vectors to calculate a final solar vector.

18. The solar sensor according to claim 17, wherein the noise is removed using an extended Kalman filter.

19. The sun position tracking method of claim 12, wherein

the at least one image sensor comprises six image sensor cameras installed at six vertexes of a virtual icosahedron to enable three of the six image sensor cameras to capture a black sun with hemispherical coverage irrespective of the position of the sun, and

the six vertexes include one reference vertex and five vertexes neighboring the reference vertex.

20. A sun position tracking method based on a black sun effect of an image sensor, comprising:

capturing one or more images using one or more image sensors; and

processing the captured one or more images using the black sun effect, comprising

estimating a center point of each black sun in the captured one or more images,

extracting solar vectors with respect to the center point of each black sun,

obtaining an initial rotation using two solar vectors represented in sensor coordinates and two solar vectors represented in reference coordinates at two different time points,

determining an average of a plurality of initial rotations calculated by changing the two different time points by a predetermined number of times as a final rotation, to transform the extracted solar vectors into the reference coordinates, and

fusing the transformed solar vectors.