近景攝影測量中人造標點的自動辨識與定位

Automatic Identification and Positioning of Artificial Targets for Close-Range Photogrammetry

王聖鐸(Sen-Do Wang)

《航測及遙測學刊》 4卷4期 (1999/12) Pp. 1-12

https://doi.org/10.6574/JPRS.1999.4(4).1

摘要

由於數位攝影測量的發展，近景攝影測量也朝自動化邁進。近景攝影測量中常以人造標點為施測目標，傳統人工量測方式不但費工且費時。如今在數位影像中自動定得人造標點的像片坐標的技術已行之有年，然而這些系統只定位而不認標，所以定出來的坐標不能與地面標點直接產生關連，也無法與重疊像片之標點直接產生共輒關係。本文所提的方法不但能自動定位，同時能辨識標號，其過程大略分為搜尋標點、標點定位、及標號辨識。利用特別設計的人造標點，結合電腦視覺領域中影像處理的技術分別以圓形標偵測元搜尋影像中的標點、以最小二乘匹配將標點定位、再利用標準化互相關係數的計算來辨識標號。依此程序設計出一套自動化的程式，並以數位像機實際拍攝三種環境下的標點：單純背景、階梯、與傾斜拍攝加以實驗。結果證實在單純背景下的確可以得到相當滿意的成果，而在階梯和傾斜30°以下時的成果也尚可接受。

關鍵字

數位攝影測量 ； 近景攝影測量 ； 圓形標偵測元 ； 自動化 ； 辨識 ； 定位

並列摘要

Due to the advance of digital photogrammetry, close-range photogrammetry steps into the door of automation. In close-range photogrammetry, artificial targets are frequently used for measurement. It was inefficient and time consuming in the past when there is no choice but manual measurement. Nowadays, automatically determining the photo coordinates from a digital image has been applied for years. However, targets are just positioned but not identified by the current systems. Therefore, the positioned targets in an image are not directly associated with the ground targets and the conjugate target points in other overlapped images. This paper proposes an approach to position targets and recognize the identifications of the positioned targets as well. The work can be divided into three steps: searching, localization, and identifying targets. First we designed a special target which consists of two digits and two round-shape targets. Then an ad hoc circular-target detector is used to search all possible round-shape targets in the image. The centers of the detected circular-targets can be precisely located by using the least squares matching. Based on the known relationship between the two digits and the two circular targets, the boundaries of the digits can be determined. Extracting the subimage of the digits and calculating the normalize cross correlation coefficients with the standard templates then the digits could be identified. To verify the proposed method, we conducted three experiments. The first experiment is to identify targets in an image with uniform white color background. All the targets were successfully and correctly identified in this experiment. The second experiment is designed to find targets in different scales, so that several sets of targets attached in the vertical sides of stairs were imaged and tested. Targets tend to be misinterpreted when their scales are getting small. The third experiment is designed to identify targets in an oblique image. This experiment shows that correct results can be obtained when the image angle is less than 30 degrees.

並列關鍵字

Digital photogrammetry ； Close-range photogrammet ； Circular-target detector ； Automation ； Identification ； Positioning.