基于激光成像技术的农药雾滴飘移评价方法研究
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摘要
为开发在风洞中农药喷雾飘移的测量方法,该文按照国际标准ISO22856,使用德国Lechler公司的LU120-01喷头在风洞中测量了有机硅、植物油等11种助剂在水平和垂直方向上的喷雾飘移,同时采用激光成像技术,结合计算机图像快速批处理,提取了雾滴云图片横纵方向的最大值及位置、重心坐标、平均值等图像特征参数,与测量结果计算得出的喷雾飘移的飘移率、特征高度、飘移潜力指数(drift potential index, DIX)进行拟合。结果表明,横纵方向的最大值及位置、重心坐标、平均值与垂直和水平飘移显著相关(Sig. F<0.05),与飘移率、特征高度、飘移潜力指数拟合的相关系数均大于0.91,最大绝对值平均相对误差仅为5.9%;垂直特征高度和水平特征距离拟合结果最好,平均相对误差为0,绝对值平均相对误差为0.6%和1.5%,其次为DIX指数和飘移率。由此表明,此方法可准确的用于评价雾滴的飘移性,测试速度比传统的测量方法更加快速,测试重复性高且无需耗材,DIX指数综合准确性高达96%,大大降低了喷雾飘移的测试成本。该研究可为风洞中的飘移测试提供一种新的测试选择。
Spray drift, which may result in a waste of pesticides and environmental risks, has been viewed as a concern in the use of pesticides. The indoor test of spray drift is mainly measured by the wind tunnel which possess a more stable and controllable wind speed. Recently, the laser is widely used in a range of fields owing to its perfect light stability and the Tyndall phenomenon is remarkable in dispersed particles. Therefore, this paper develops a new method for measuring the drift of pesticide spray in wind tunnels. According to the international standard ISO22856, 11 kinds of additives such as silicone and vegetable oil were measured in the wind tunnel using LU120-01 nozzle from Lechler, Germany. Each additive adjuvant liquid was sprayed for 5 s, repeated 3 times. The collectors were Polytetrafluoroethylene(PTFE) lines and Polyvinyl Chloride(PVC) cards. The PTFE lines were placed at a distance of 2 m from the nozzle in the downwind direction and were 5-85 cm in height(interval 10 cm). The collected droplet particles were analyzed by LS-55 fluorescence analyzer. At the same time, laser imaging technology was used to continuously image during the spraying process. The exposure time is 1/8 s, the ISO is 100 and the aperture is f/1.8. The shutter was controlled by Bluetooth Controller. Combined with computer image rapid batch processing, RGB three-color layer was filtered by MATLAB 2017 a, and R-layer minus G-layer image was calculated. The maximum value of gray level and the image feature parameters such as position, barycentric coordinates, and the average value in the horizontal and vertical directions of the image were extracted. The drift rate, feature height and drift potential index(DIX) of the spray drift were calculated from the actual measurement results. The calculated result was fitting with the measured result. The fitting results showed that the maximum value and position of maximum in the x and y axis, the center of gravity coordinates, and the mean value were significantly correlated(Sig. F<0.05) with the drift rate, drift feature height, and DIX. The correlation coefficient was greater than 0.91, the maximum absolute value relative error was only 5.9%. The fitting results of vertical feature height and horizontal feature distance were the best, the average relative error was 0, the absolute relative error was 0.6% and 1.5%(vertical and horizontal direction), followed by DIX index(the absolute relative error of the vertical and horizontal direction were 4.8% and 3.2%) and drift rate(the absolute relative error of the vertical and horizontal direction were 5.9% and 5.3%). It showed that this method could be used to evaluate the drift of droplets accurately. The test speed was faster than the traditional measurement method, and one picture only cost less 1 s for calculation. The test repeatability was high, the DIX index had a comprehensive accuracy of 96%. The test was no needed consumables, which greatly reduced the costing of spray drift testing. The measurement of spray drift in wind tunnels based on laser imaging is an evaluation method that can give one more choice for spraying drift testing.
Spray drift, which may result in a waste of pesticides and environmental risks, has been viewed as a concern in the use of pesticides. The indoor test of spray drift is mainly measured by the wind tunnel which possess a more stable and controllable wind speed. Recently, the laser is widely used in a range of fields owing to its perfect light stability and the Tyndall phenomenon is remarkable in dispersed particles. Therefore, this paper develops a new method for measuring the drift of pesticide spray in wind tunnels. According to the international standard ISO22856, 11 kinds of additives such as silicone and vegetable oil were measured in the wind tunnel using LU120-01 nozzle from Lechler, Germany. Each additive adjuvant liquid was sprayed for 5 s, repeated 3 times. The collectors were Polytetrafluoroethylene(PTFE) lines and Polyvinyl Chloride(PVC) cards. The PTFE lines were placed at a distance of 2 m from the nozzle in the downwind direction and were 5-85 cm in height(interval 10 cm). The collected droplet particles were analyzed by LS-55 fluorescence analyzer. At the same time, laser imaging technology was used to continuously image during the spraying process. The exposure time is 1/8 s, the ISO is 100 and the aperture is f/1.8. The shutter was controlled by Bluetooth Controller. Combined with computer image rapid batch processing, RGB three-color layer was filtered by MATLAB 2017 a, and R-layer minus G-layer image was calculated. The maximum value of gray level and the image feature parameters such as position, barycentric coordinates, and the average value in the horizontal and vertical directions of the image were extracted. The drift rate, feature height and drift potential index(DIX) of the spray drift were calculated from the actual measurement results. The calculated result was fitting with the measured result. The fitting results showed that the maximum value and position of maximum in the x and y axis, the center of gravity coordinates, and the mean value were significantly correlated(Sig. F<0.05) with the drift rate, drift feature height, and DIX. The correlation coefficient was greater than 0.91, the maximum absolute value relative error was only 5.9%. The fitting results of vertical feature height and horizontal feature distance were the best, the average relative error was 0, the absolute relative error was 0.6% and 1.5%(vertical and horizontal direction), followed by DIX index(the absolute relative error of the vertical and horizontal direction were 4.8% and 3.2%) and drift rate(the absolute relative error of the vertical and horizontal direction were 5.9% and 5.3%). It showed that this method could be used to evaluate the drift of droplets accurately. The test speed was faster than the traditional measurement method, and one picture only cost less 1 s for calculation. The test repeatability was high, the DIX index had a comprehensive accuracy of 96%. The test was no needed consumables, which greatly reduced the costing of spray drift testing. The measurement of spray drift in wind tunnels based on laser imaging is an evaluation method that can give one more choice for spraying drift testing.
引文
[1]Gil E,Balsari P,Gallart M,et al.Determination of drift potential of different flat fan nozzles on a boom sprayer using a test bench[J].Crop Protection,2014,56(2):58-68.
[2]袁会珠,杨代斌,闫晓静,等.农药有效利用率与喷雾技术优化[J].植物保护,2011,37(5):14-20.Yuan Huizhu,Yang Daibin,Yan xiaojing,et al.Pesticideefficiency and the way to optimize the spray application[J].Plant Protection,2011,37(5):14-20.(in Chinese with English abstract)
[3]谢晨,宋坚利,何雄奎,等.两类扇形雾喷头雾化过程比较研究[J].农业工程学报,2013,29(5):25-30.Xie Chen,Song Jianli,He Xiongkui et al.Comparative research of atomization process for two kinds of flat fan nozzle[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(5):25-30.(in Chinese with English abstract)
[4]Otto S,Loddo D,Baldoin C,et al.Spray drift reduction techniques for vineyards in fragmented landscapes[J].Journal of Environmental Management,2015,162(2):290-298.
[5]王潇楠,何雄奎,Andreas.Herbst,等.喷杆式喷雾机雾滴飘移测试系统研制及性能试验[J].农业工程学报,2014,30(18):55-62.Wang Xiaonan,He Xiongkui,Andreas.Herbst,et al.Development and performance test of spray drift test system for sprayer with bar[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2014,30(18):55-62.(in Chinese with English abstract)
[6]Van Zyl S A,Brink J C,Calitz F J,et al.Effects of adjuvants on deposition efficiency of fenhexamid sprays applied to Chardonnay grapevine foliage[J].Crop Protection,2010,29(2):843-852.
[7]石伶俐,陈福良,郑斐能,等.喷雾助剂对三唑磷在水稻叶片上沉积量的影响[J].中国农业科学,2009,42(12):4228-4233.Shi Lingli,Chen Fuliang,Zheng Feineng,et al.The influence of triazophos deposition on rice leaves by adding spray adjuvants[J].Scientia Agricultural Sinica,2009,42(12):4228-4233.(in Chinese with English abstract)
[8]Nita M,Ellis M A,Wilson L L,et al.Evaluation of the curative and protectant activity of fungicides and fungicide adjuvant mixtures on Phomopsiscane and leaf spot of grape:A controlled environment study[J].Crop Protection,2007,26(9):1377-1384.
[9]郭善竹,张丽,张凯,等.Silwet系列农用有机硅在水稻害虫防治中的应用[J].中国农技推广,2008,24(4):41-42.Guo Shanzhu,Zhang Li,Zhang Kai,et al.Application of agricultural Silwet series silicone pest control for rice[J].China Agricultural Technology Extension,2008,24(4):41-42.(in Chinese with English abstract)
[10]朱金文,李洁,吴志毅,等.有机硅喷雾助剂对草甘膦在空心莲子草上的沉积和生物活性的影响[J].农药学学报,2011,13(2):192-196.Zhu Jinwen,Li Jie,Wu Zhiyi,et al.Influence of organosilicone adjuvant on deposition and phytotoxicity of glyphosate against Alternanthera philoxeroides[J].Chinese Journal of Pesticide Science,2011,13(2):192-196.(in Chinese with English abstract)
[11]Thomson S J,Smith L A,Hanks J E.Evaluation of application accuracy and performance of a hydraulically operated variable-rate aerial application system[J].Transactions of the Asabe,2009,52(3):715-722.
[12]Kirk I W,Hoffmann W C,FRITZ B K.Aerial application methods for increasing spray deposition on wheat heads[J]Applied Engineering in Agriculture,2007,23(6):357-364.
[13]Miller P C H,Ganzelmeier H,et al.The international(BCPC)spray classification system including a drift potential factor[C]//Proceedings of the Brighton Crop Protection Conference-Weeds,1997:371-380.
[14]Herbst A.A method to determine spray drift potential from nozzles and its link to buffer zone restrictions[C]//2001ASAE Annual Meeting.American Society of Agricultural and Biological Engineers,1998:1.
[15]傅泽田,祁力钧.风洞实验室喷雾飘移试验[J].农业工程学报,1999,15(1):109-112.Fu Zetian,Qi Lijun.Wind tunnel spraying drift measurements[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),1999,15(1):109-112.(in Chinese with English abstract)
[16]曾爱军,何雄奎,陈青云,等.典型液力喷头在风洞环境中的飘移特性试验与评价[J].农业工程学报,2005,21(10):78-81.Zeng Aijun,He Xiongkui,Chen Qingyun,et al.Spray drift potential evaluation of typical nozzles under wind tunnel conditions[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2005,21(10):78-81.(in Chinese with English abstract)
[17]王潇楠,何雄奎,宋坚利,等.助剂类型及浓度对不同喷头雾滴飘移的影响[J].农业工程学报,2015,31(22):49-55.Wang Xiaonan,He Xiongkui,Song Jianli,et al.Effect of adjuvant types and concentration on spray drift potential of different nozzles[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(22):49-55.(in Chinese with English abstract)
[18]Cooper J F,Smith D N,Dobson H M.An evaluation of two field samplers for monitoring spray drift[J].Crop Protection,1996,15(3):249-257.
[19]Fritz B K.Meteorological effects on deposition and drift of aerially applied sprays[J].Transactions of the Asabe,2006,49(5):1295-1301.
[20]吕晓兰,傅锡敏,宋坚利,等.喷雾技术参数对雾滴飘移特性的影响[J].农业机械学报,2011,42(1):59-63.LüXiaolan,Fu Ximin,Song Jianli,et al.Influence of spray operating parameters on spray drift[J].Transactions of the Chinese Society for Agricultural Machinery,2011,42(1):59-63.(in Chinese with English abstract)
[21]张慧春,郑加强,周宏平,等.农药喷施过程中雾滴沉积分布与脱靶飘移研究[J].农业机械学报,2017,48(8):114-122.Zhang Huichun,Zheng Jiaqiang,Zhou Hongping,et al.Droplet deposition distribution and off-target drift during pesticide spraying operation[J].Transactions of the Chinese Society for Agricultural Machinery,2017,48(8):114-122.
[22]Vol N.Pesticide tracers for measuring orchard spray drift[J].Applied Engineering in Agriculture,1993,9(9):501-505.
[23]Richardson B,Thistle H W.Measured and predicted aerial spray interception by a young Pinus radiata canopy[J].Transactions of the ASABE,2006,49(1):15-23.
[24]Bonds J A S,Greer M J,Fritz B K,et al.Aerosol sampling:Comparison of two rotating impactors for field droplet sizing and volumetric measurements[J].Journal of the American Mosquito Control Association,2009,25(4):474-480.
[25]张慧春,Gary Dorr,郑加强,等.喷雾飘移的风洞试验和回归模型[J].农业工程学报,2015,31(3):94-100.Zhang Huichun,Gary Dorr,Zheng Jiaqiang,et al.Wind tunnel experiment and regression model for spray drift[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(3):94-100.(in Chinese with English abstract)
[26]Ould-Dada Z,Baghini N M.Resuspension of small particles from tree surfaces[J].Atmospheric Environment,2001,35(22):3799-3809.
[27]Gil E,Llorens J,Llop J,et al.Use of a terrestrial LIDARsensor for drift detection in vineyard spraying[J].Sensors,2013,13(1):516-534.
[28]Gregorio E,Rosell-Polo J R,Sanz R,et al.LIDAR as an alternative to passive collectors to measure pesticide spray drift[J].Atmospheric Environment,2014,82:83-93.
[29]王潇楠,何雄奎,王昌陵,等.油动单旋翼植保无人机雾滴飘移分布特性[J].农业工程学报,2017,33(1):117-123.Wang Xiaonan,He Xiongkui,Wang Changling,et al.Spray drift characteristics of fuel powered single-rotor UAV for plant protection[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2017,33(1):117-123.(in Chinese with English abstract)
[30]曾爱军.减少农药雾滴飘移的技术研究[D].北京:中国农业大学,2005.Zeng Aijun.Research on Technique to Reduce Spray Droplets Drift[D].Beijing:China Agricultural University,2005.(in Chinese with English abstract)
[31]谭峰,高艳萍.基于图像的植物叶面积无损测量方法研究[J].农业工程学报,2008,24(5):170-173.Tan Feng,Gao Yanping.Investigation of the method for non-destructive measurement of leaf area based on image[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2008,24(5):170-173.(in Chinese with English abstract)
[32]廖士中,高培焕,苏艺,等.一种光学镜头摄像机图像几何畸变的修正方法[J].中国图像图形学报,2000,5(7):593.Liao Shizhong,Gao Peihuan,Su Yi,et al.A geometric rectification method for lens camera[J].Journal of Image and Graphics,2000,5(7):593.(in Chinese with English abstract)
[2]袁会珠,杨代斌,闫晓静,等.农药有效利用率与喷雾技术优化[J].植物保护,2011,37(5):14-20.Yuan Huizhu,Yang Daibin,Yan xiaojing,et al.Pesticideefficiency and the way to optimize the spray application[J].Plant Protection,2011,37(5):14-20.(in Chinese with English abstract)
[3]谢晨,宋坚利,何雄奎,等.两类扇形雾喷头雾化过程比较研究[J].农业工程学报,2013,29(5):25-30.Xie Chen,Song Jianli,He Xiongkui et al.Comparative research of atomization process for two kinds of flat fan nozzle[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2013,29(5):25-30.(in Chinese with English abstract)
[4]Otto S,Loddo D,Baldoin C,et al.Spray drift reduction techniques for vineyards in fragmented landscapes[J].Journal of Environmental Management,2015,162(2):290-298.
[5]王潇楠,何雄奎,Andreas.Herbst,等.喷杆式喷雾机雾滴飘移测试系统研制及性能试验[J].农业工程学报,2014,30(18):55-62.Wang Xiaonan,He Xiongkui,Andreas.Herbst,et al.Development and performance test of spray drift test system for sprayer with bar[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2014,30(18):55-62.(in Chinese with English abstract)
[6]Van Zyl S A,Brink J C,Calitz F J,et al.Effects of adjuvants on deposition efficiency of fenhexamid sprays applied to Chardonnay grapevine foliage[J].Crop Protection,2010,29(2):843-852.
[7]石伶俐,陈福良,郑斐能,等.喷雾助剂对三唑磷在水稻叶片上沉积量的影响[J].中国农业科学,2009,42(12):4228-4233.Shi Lingli,Chen Fuliang,Zheng Feineng,et al.The influence of triazophos deposition on rice leaves by adding spray adjuvants[J].Scientia Agricultural Sinica,2009,42(12):4228-4233.(in Chinese with English abstract)
[8]Nita M,Ellis M A,Wilson L L,et al.Evaluation of the curative and protectant activity of fungicides and fungicide adjuvant mixtures on Phomopsiscane and leaf spot of grape:A controlled environment study[J].Crop Protection,2007,26(9):1377-1384.
[9]郭善竹,张丽,张凯,等.Silwet系列农用有机硅在水稻害虫防治中的应用[J].中国农技推广,2008,24(4):41-42.Guo Shanzhu,Zhang Li,Zhang Kai,et al.Application of agricultural Silwet series silicone pest control for rice[J].China Agricultural Technology Extension,2008,24(4):41-42.(in Chinese with English abstract)
[10]朱金文,李洁,吴志毅,等.有机硅喷雾助剂对草甘膦在空心莲子草上的沉积和生物活性的影响[J].农药学学报,2011,13(2):192-196.Zhu Jinwen,Li Jie,Wu Zhiyi,et al.Influence of organosilicone adjuvant on deposition and phytotoxicity of glyphosate against Alternanthera philoxeroides[J].Chinese Journal of Pesticide Science,2011,13(2):192-196.(in Chinese with English abstract)
[11]Thomson S J,Smith L A,Hanks J E.Evaluation of application accuracy and performance of a hydraulically operated variable-rate aerial application system[J].Transactions of the Asabe,2009,52(3):715-722.
[12]Kirk I W,Hoffmann W C,FRITZ B K.Aerial application methods for increasing spray deposition on wheat heads[J]Applied Engineering in Agriculture,2007,23(6):357-364.
[13]Miller P C H,Ganzelmeier H,et al.The international(BCPC)spray classification system including a drift potential factor[C]//Proceedings of the Brighton Crop Protection Conference-Weeds,1997:371-380.
[14]Herbst A.A method to determine spray drift potential from nozzles and its link to buffer zone restrictions[C]//2001ASAE Annual Meeting.American Society of Agricultural and Biological Engineers,1998:1.
[15]傅泽田,祁力钧.风洞实验室喷雾飘移试验[J].农业工程学报,1999,15(1):109-112.Fu Zetian,Qi Lijun.Wind tunnel spraying drift measurements[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),1999,15(1):109-112.(in Chinese with English abstract)
[16]曾爱军,何雄奎,陈青云,等.典型液力喷头在风洞环境中的飘移特性试验与评价[J].农业工程学报,2005,21(10):78-81.Zeng Aijun,He Xiongkui,Chen Qingyun,et al.Spray drift potential evaluation of typical nozzles under wind tunnel conditions[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2005,21(10):78-81.(in Chinese with English abstract)
[17]王潇楠,何雄奎,宋坚利,等.助剂类型及浓度对不同喷头雾滴飘移的影响[J].农业工程学报,2015,31(22):49-55.Wang Xiaonan,He Xiongkui,Song Jianli,et al.Effect of adjuvant types and concentration on spray drift potential of different nozzles[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(22):49-55.(in Chinese with English abstract)
[18]Cooper J F,Smith D N,Dobson H M.An evaluation of two field samplers for monitoring spray drift[J].Crop Protection,1996,15(3):249-257.
[19]Fritz B K.Meteorological effects on deposition and drift of aerially applied sprays[J].Transactions of the Asabe,2006,49(5):1295-1301.
[20]吕晓兰,傅锡敏,宋坚利,等.喷雾技术参数对雾滴飘移特性的影响[J].农业机械学报,2011,42(1):59-63.LüXiaolan,Fu Ximin,Song Jianli,et al.Influence of spray operating parameters on spray drift[J].Transactions of the Chinese Society for Agricultural Machinery,2011,42(1):59-63.(in Chinese with English abstract)
[21]张慧春,郑加强,周宏平,等.农药喷施过程中雾滴沉积分布与脱靶飘移研究[J].农业机械学报,2017,48(8):114-122.Zhang Huichun,Zheng Jiaqiang,Zhou Hongping,et al.Droplet deposition distribution and off-target drift during pesticide spraying operation[J].Transactions of the Chinese Society for Agricultural Machinery,2017,48(8):114-122.
[22]Vol N.Pesticide tracers for measuring orchard spray drift[J].Applied Engineering in Agriculture,1993,9(9):501-505.
[23]Richardson B,Thistle H W.Measured and predicted aerial spray interception by a young Pinus radiata canopy[J].Transactions of the ASABE,2006,49(1):15-23.
[24]Bonds J A S,Greer M J,Fritz B K,et al.Aerosol sampling:Comparison of two rotating impactors for field droplet sizing and volumetric measurements[J].Journal of the American Mosquito Control Association,2009,25(4):474-480.
[25]张慧春,Gary Dorr,郑加强,等.喷雾飘移的风洞试验和回归模型[J].农业工程学报,2015,31(3):94-100.Zhang Huichun,Gary Dorr,Zheng Jiaqiang,et al.Wind tunnel experiment and regression model for spray drift[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(3):94-100.(in Chinese with English abstract)
[26]Ould-Dada Z,Baghini N M.Resuspension of small particles from tree surfaces[J].Atmospheric Environment,2001,35(22):3799-3809.
[27]Gil E,Llorens J,Llop J,et al.Use of a terrestrial LIDARsensor for drift detection in vineyard spraying[J].Sensors,2013,13(1):516-534.
[28]Gregorio E,Rosell-Polo J R,Sanz R,et al.LIDAR as an alternative to passive collectors to measure pesticide spray drift[J].Atmospheric Environment,2014,82:83-93.
[29]王潇楠,何雄奎,王昌陵,等.油动单旋翼植保无人机雾滴飘移分布特性[J].农业工程学报,2017,33(1):117-123.Wang Xiaonan,He Xiongkui,Wang Changling,et al.Spray drift characteristics of fuel powered single-rotor UAV for plant protection[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2017,33(1):117-123.(in Chinese with English abstract)
[30]曾爱军.减少农药雾滴飘移的技术研究[D].北京:中国农业大学,2005.Zeng Aijun.Research on Technique to Reduce Spray Droplets Drift[D].Beijing:China Agricultural University,2005.(in Chinese with English abstract)
[31]谭峰,高艳萍.基于图像的植物叶面积无损测量方法研究[J].农业工程学报,2008,24(5):170-173.Tan Feng,Gao Yanping.Investigation of the method for non-destructive measurement of leaf area based on image[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2008,24(5):170-173.(in Chinese with English abstract)
[32]廖士中,高培焕,苏艺,等.一种光学镜头摄像机图像几何畸变的修正方法[J].中国图像图形学报,2000,5(7):593.Liao Shizhong,Gao Peihuan,Su Yi,et al.A geometric rectification method for lens camera[J].Journal of Image and Graphics,2000,5(7):593.(in Chinese with English abstract)