PRINCIPLE,SOFTWARE AND EXPERIMENT OF GPS-SUPPORTED AEROTRIANGULATION

In conventional aerial photogrammetry, the high accurate photogrammetric point determination is always carried out by aerotriangulation using a great deal of ground control points around the perimeter and in the center of block area because the exterior orien- tation parameters of aerial photographs are unknown. A technological revolution in pho- togrammetry has taken place since Navstar global positioning system (GPS) was applied to determine the 3D coordinates of exposure station positions during the photo flight missions. GPS-supported aerotriangulation is conducted by a combined bundle adjustment for pho- togrammetric observations and the camera orientation data. In this case, the essential ground control points are replaced by GPS-determined camera positions. Recent investigations show this method is coming to the practice. We have been engaged in the theoretical studies, soft- ware development, and related experiments and production in the field since 1990. So far the abundant research achievements are obtained in terms of the theory and application. In this paper,we first derives the mathematical model of GPS-supported aerotriangulation from the geometry between camera and airborne GPS antenna, then describes briefly a software pack- age WuCAPS (Wuhan combined adjustment program system) developed newly by the au- thor,which serves the purpose of the combined bundle adjustment for photogrammetric and non-photogrammetric observations. At the end of the present work, a set of actual aerial pho- tographs,at the image scale of 1: 34 000, with airborne GPS data taken from Tianjing site, China were processed by WuCAPS. The empirical results have verified that the accuracy of the combined bundle adjustment with 4 XYZ ground control points around the corners of block area is very close to that of the conventional bundle adjustment with 3 additional pa- rameters, that leads to reduce 88% field survey and 75% production cost, and can meet the specification of topographic mapping at small or medium scale by GPS-supported aerotriangu- lation without ground control. This shows the ample applicability and the economic benefit of kinematic GPS relative positioning in high accurate photogrammetric point determination.

Cascaded navigation control for agricultural vehicles tracking straight paths

In precision agriculture(PA),an agricultural vehicle navigation system is essential and the navigation control accuracy is important in this system.As straight path tracking is the major operating mode of agricultural vehicles on large fields,a cascaded navigation control method for straight path tracking is proposed in this study.Firstly,a cascaded navigation control structure for the agricultural vehicle was discussed.Based on this structure,the navigation control task was decomposed into two cascaded control tasks,namely,the path tracking control task and the steering control task.Secondly,a relative kinematics model of agricultural vehicles was deduced,and an optimal Proportional-Derivative(PD)method based on the deduced model was developed in the path tracking control task.Then,an improved PD method based on a transition process was proposed in the steering control task to enhance the performance of the steering control subsystem.Finally,the effectiveness and the superiority of the proposed method were verified by a series of experiments.Results of the experimental data analysis show that mean value of the lateral position deviation is 0.02 m and standard deviation of the lateral position deviation is 0.04 m,which proves that the proposed method has achieved satisfactory effects on the straight path tracking of agricultural vehicles.