發(fā)布時間：2018-04-15 11:23

  本文選題：無人機 + 魚眼矯正��； 參考：《電子科技大學》2017年碩士論文

【摘要】：近年來,無人機憑借使用方便、成本低廉的優(yōu)點,成為了各領域應用的“新寵”,如環(huán)境監(jiān)測、媒體報道、電商快遞等。由于外界環(huán)境復雜,無人機的GPS信號存在丟失或者干擾的可能,此時基于視覺的導航方式就顯得尤為重要。目前已有許多針對視覺導航的研究,但已實地應用的方法較少。本文基于無人機自主飛行項目撰寫,工作重點之一為研究圖像畸變矯正方法和圖像拼接技術,工作重點之二是自主降落階段的地標設計與識別。針對無人機利用航拍相機采集的圖片容易產生畸變的問題,本文首先分析了相機的成像原理,選用張正友標定法對相機進行標定。先制作棋盤格標定板,用航拍相機采集標定版不同方位角的圖像,提取Harris角點,計算得到相機的內外參數(shù)矩陣和畸變系數(shù),再利用極大似然估計對內外參數(shù)和畸變系數(shù)進行優(yōu)化。最后,利用畸變系數(shù)矯正圖像,得到較好的矯正結果。圖像拼接時,本文采用基于SIFT特征的圖像拼接技術,先提取待拼接地圖的SIFT特征點,生成128維的特征向量描述子,計算兩張待拼接圖片的特征點匹配情況。為了過濾誤匹配點,首先采用最小距離和次小距離的比值進行篩選,對篩選出來的候選匹配點對,再利用RANSAC算法進行優(yōu)化,誤匹配點比例降低了74.74%。根據(jù)選出的匹配點對計算得到代表圖像變換關系的單應性矩陣,用單應性矩陣將待拼接圖像像素變換到基準圖像坐標系,生成拼接圖。本文提出了平均融合法和加權平均融合法對圖像的重合區(qū)域進行像素融合,均得到了較好的拼接結果。最后,本文實現(xiàn)了多幅地圖的自動拼接算法。自主降落部分,本文設計了簡單易識別的H地標,對獲取的降落圖像進行預處理得到灰度圖,再將自適應閾值法應用到灰度圖的二值化中,提取圖像中的輪廓,依據(jù)輪廓的長度和面積等信息,過濾出非地標輪廓。最后在候選輪廓中,利用形狀的Hu不變矩判斷是否是降落標志輪廓。本項目改進了H地標,增加輪廓邊緣,并且將自適應閾值法應用于圖像二值化中,增強了地標在各種環(huán)境下的魯棒性。本文還提出了一套能夠實現(xiàn)低空小范圍內視覺降落的四旋翼無人機軟硬件方案,并在電子科技大學清水河校區(qū)驗證了視覺自主降落系統(tǒng)的可行性、穩(wěn)定性和準確性,實驗表明降落精度能夠達到設計要求的1米。
[Abstract]:In recent years, unmanned aerial vehicles (UAVs) have become "new favorites" for various applications, such as environmental monitoring, media reports, e-commerce couriers and so on, because of their advantages of convenience and low cost.Because of the complexity of the external environment, the GPS signal of UAV may be lost or interfered, so the vision-based navigation is particularly important.At present, there have been many researches on visual navigation, but few methods have been applied in the field.Based on UAV autonomous flight project, one of the key tasks is to study image distortion correction method and image splicing technology, and the second is to design and identify landmarks in autonomous landing stage.Aiming at the problem that the images collected by aerial camera are easily distorted, this paper first analyzes the imaging principle of the camera, and uses the calibration method of Zhang Zhengyou to calibrate the camera.First, the checkerboard was made, and the images of different azimuth angles of the calibration plate were collected by aerial camera. The Harris corner was extracted, and the internal and external parameter matrix and distortion coefficient of the camera were calculated.Then the maximum likelihood estimation is used to optimize the internal and external parameters and distortion coefficients.Finally, the distortion coefficient is used to correct the image, and a better correction result is obtained.In this paper, the image stitching technique based on SIFT features is used to extract the SIFT feature points of the map to be stitched, and a 128-dimensional feature vector descriptor is generated to calculate the matching of the feature points of the two images to be stitched.In order to filter the mismatched points, the ratio of the minimum distance to the sub-small distance is first used to screen the candidate matching points, and then the RANSAC algorithm is used to optimize the mismatch points. The ratio of the mismatched points is reduced by 74.74 points.According to the selected matching point pairs, the monogram matrix representing the image transformation relationship is obtained, and the pixels of the image to be stitched are transformed into the reference image coordinate system by the homotropic matrix to generate the splicing image.In this paper, an average fusion method and a weighted average fusion method are proposed for pixel fusion of the overlapped region of an image, and good results are obtained.Finally, this paper realizes the automatic mosaic algorithm of multiple maps.In the part of autonomous landing, we design a simple and easily recognizable H landmark, preprocess the landing image to get the gray image, and then apply the adaptive threshold method to the binarization of the gray image to extract the contour of the image.According to the length and area of the contour, the non-Landmark contour is filtered out.Finally, in the candidate contour, Hu invariant moment of shape is used to judge whether it is a descent mark contour.In this project, the H landmarks are improved, the contour edges are increased, and the adaptive threshold method is applied to the binarization of images, which enhances the robustness of the landmarks in various environments.This paper also proposes a software and hardware scheme of four-rotor UAV which can achieve visual landing in low altitude and small range, and verifies the feasibility, stability and accuracy of the visual autonomous landing system in Qingshuihe Campus of the University of Electronic Science and Technology.The experiment shows that the precision of landing can meet the design requirement of 1 meter.
【學位授予單位】：電子科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：V279;TP391.41

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本文編號：1753924