Research On Airborne LiDAR Simultaneous Image For Direct Geo-referencing

Airborne LiDAR is a relatively new type of remote sensing data acquisition system.A commercial airborne LiDAR system is generally integrated by a number of hardware components,mainly including:A Global Positioning System,a laser scanner and an inertial measurement unit(IMU).If you are equipped with a measuring digital camera(and the camera's internal azimuth elements and distortion is known),LiDAR system can not only quickly get high precision point cloud data in the survey area,but also can get synchronous optical image.Point cloud data and optical image fusion processing is of great significance to the application of related fields.Since the LiDAR system equipped with GPS and IMU,you can get a digital camera exterior orientation value at the moment of photography,which can be directly georeferencing.An important prerequisite for direct georeferencing is that the IMU coordinate system remains strictly parallel to the camera body coordinate system.However,due to the installation process reasons,there is a spin angle between the IMU coordinate system and the camera body coordinate system,this is the camera placement angle error.If you do not eliminate this angle error will affect the accuracy of direct direct georeferencing.In this paper,we mainly study the method of eliminating the error of camera placement in the direct georeferencing process,which can improve the accuracy of the exterior orientation elements,so it has important theoretical and practical value.The main contents are divided into the following aspects:(1)The introduction about airborne LiDAR system and analyze the error of the image direct georeferencing caused by the placement angle error.This paper introduces the composition and development status of the airborne LiDAR system,compares the similarities and differences between the point cloud data and the optical image;this paper introduces the common methods of direct georeferencing of images at present,and quantitatively analyzes the direct georeferencing accuracy caused by the camera placement angle error.(2)The efficiency of automatically extracting image connection points by matching algorithm is analyzed.The overall technical scheme adopted in this paper is divided into the steps of automatic selection of image connection points,forward intersection with elevation constraints,and checking the placement angle error.Among them,image connection point extraction has always been a time-consuming task.Using the method of point cloud data as an assistant,by means of experimental to analysis the efficiency of automatic connection of image connection points,and the most suitable algorithm to solve the problem is selected to improve the efficiency of the whole algorithm.(3)This paper introduces the calculation method of placement angle error in airborne LiDAR system.After the image connection point is extracted,then use the forward intersection method with elevation constraints to get the geographical coordinates of the image point,and interpolate the point cloud data to get the elevation correction value,then back to the image space,get the original point of the inverse coordinates.The distance between the algorithm coordinates and the coordinates of the original point is the minimum condition,and the error of the placement angle is solved iteratively to realize the correction of the external azimuth element,so that the image can be directly georeferencing.Finally,the accuracy evaluation.