The Study On Stumpages’s Factors Recognition Based On Ordinary Digital Camera

Based on the Tsai’s calibration technique, the paper measures the stumpages’ DBH and height byusing an ordinary digital camera. This research mainly focuses on three aspects:(1)While measure thesingle stumpage’s DBH, analysis the influence of lens focal length and shooting distance on accuracy;establish an effective model to correct the error caused by non-coplanar; achieve the goal of separatecamera calibration.(2)During the process of DBH measurement of the multi-stumpages, combine theTsai’s calibration technique and the ratio between the numbers of pixels to calculate the regularstumpages; establish an effective model and calculate the random stumpages with the distance betweenthe stumpages; achieve the goal of calculating all stumpages’ DBH without camera calibration in thecase of measure the true value of one stumpage’s DBH.(3)During the procedure of height measurementof the stumpage, combine the Tsai’s calibration technique and the ratio between the numbers of pixels;use the lens focal length instead of the effective focal length when calculate the multi-stumpages.Those researches show that using an ordinary digital camera based on the Tsai’s calibrationtechnique measure the stumpages’ DBH and height to get high-accuracy, and this method is simple,feasible and effective. While measure the single stumpage’s DBH, the middle-focus lens get higheraccuracy than the wide-angle lens, and the average relative error is1.36%; shooting distance has a directinfluence on accuracy, when the shooting distance is too close, the average relative error is reducedfrom the original8.84%to1.71%by an error correction model; the minimum average relative error is3.39%when calibrating camera separately. During the process of DBH measurement of themulti-stumpages, the average relative error is3.79%for the regular stumpages while the averagerelative error is5.42%for random stumpages; the average relative error is5.49%when only measurethe true value of one stumpage’s DBH without camera calibration. During the procedure of heightmeasurement of the stumpage, the average relative error is4.4.7%for the single stumpage while theaverage relative error is6.73%for the multi-stumpages.There are two aspects of innovations in this study:(1)Achieving the goal of separation cameracalibration, can do multiple measurements that only need one calibration. As a result, the methodimproves measurement efficiency.(2)Measuring random stumpages by using one image, there is noneed to use stereo vision to recover stumpage’s3-D word coordinates.