| In traditional GPS auxiliary aerial triangulation,the process of GPS data usually adopts differential positioning mode.Therefore,it is necessary to set up a ground reference station at an appropriate position in the survey area when the UAV is flying.When the aerial photography range is large,Setting up a reference station has become a time-consuming and labor-intensive task,because the base stations that need to be set up along with the increase of the survey area have to be increased,which greatly increases the difficulty of aerial survey operations.Although the GPS-supported bundle block adjustmen,to a certain extent,can solve the dependence problem of low altitude photogrammetry on ground control points,When the UAV is used for photogrammetry,the UAV cannot maintain a uniform flying state.Instantaneous speed and instantaneous direction of the UAV are different when the camera is exposed.That is,the impact of exposure delay error at each exposure point is inconsistent.It is obviously unreasonable to use traditional methods to compensate for the exposure delay error.Based on the above problems,this paper proposes a GPS Supported bundle adjustment that takes into account the exposure delay based on the precise single-point positioning technique combined with the latest airborne research results.This method is a further extension of the scope of application of traditional GPS Supported bundle adjustment.It is hoped that based on the traditional GPS Supported bundle adjustment,the accuracy of null three encryption will be further improved and the work flow of aerial photogrammetry can be simplified.In this thesis,the basic principles of precise single-point positioning and GPS-assisted aerial triangulation are introduced firstly,then the exposure delay mechanism is clarified,and then the theoretical basis and mathematical model of GPS assisted beam method regional network adjustment taking into account the exposure delay are introduced.The three-dimensional coordinate acquisition method and technical flow of the UAV camera site supported by the precise single-point positioning technology are described.Then,the flow of the UAV acquisition of ground image data is described.Finally,the experimental data obtained are used for comparative test analysis.The experimental scheme mainly includes: the comparative analysis of precise point positioning results and differential positioning results,a comparative experiment of the results of the GPS assisted beam method under the support of the regional network adjustment and differential positioning of the GPS assisted beam method with the exposure delay,the influence of control points without ground control on adjustment of GPS aided bundle adjustment with consideration of exposure delay.Finally,the feasibility of the precise point positioning technology in the adjustment of GPS aided beam area network taking into account the exposure delay is analyzed in detail.The experimental results show that the coordinates obtained by the precise point positioning technology and the coordinates obtained by differential positioning are completely different.However,for a single airline,its error appears to be systematic.When adopting the control scheme of four-corner arrangement of ground level ground control points,applying the positioning results obtained by differential and precise single-point positioning techniques respectively to GPS-assisted aerial triangulation can achieve basically the same adjustment results,thereby verifying the accuracy of single-point positioning techniques can be applied as effectively in GPS-assisted aerial triangulation as differential positioning techniques.The adjustment of GPS aided beam area network taking into account the exposure delay shows that after considering the exposure delay factor,the accuracy of GPS assisted aerial triangulation can be effectively improved.The result shows that the adjustment result without ground control can only meet the accuracy requirements of small and medium scale mapping. |
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