Friends who have produced LIDAR point cloud data must know that if we produce 1:500 high-precision data, only using lidar data can only meet the demand of accurate elevation data in many cases, and many ground objects can only be drawn with the help of Orthophoto images. For the survey area with housing area in the survey area, it is sometimes difficult to draw the housing structure and accessories if we want to meet the standard of 1:500 topographic map, Therefore, we recommend the use of tilt + laser for high-precision rendering. The laser solves the elevation in the forest and the model solves the rendering of ground objects.
We take a recent project as an example to introduce the method of linkage production. Upon receiving the demand of Party A, the 1:500 topographic map of the survey area shall be drawn. The elevation accuracy is required to be high, and the project is very urgent. According to the satellite map of the survey area, the survey area covers an area of about 1 square kilometer. The survey area belongs to suburban hilly terrain with dense vegetation and a large number of houses and features. If the UAV is fully used with lidar for data acquisition, it is difficult to draw buildings and other ground objects. It is decided to use the combination of tilt model and lidar to collect the topographic map, and carry out manual adjustment and drawing where necessary.
The project uses m300rtk to carry P1 for swing flight. After the flight, replace RIEGL 250 laser for laser scanning of simulated flight. There were 6 swing flights and 4 laser scanning flights, with 21 image control points and inspection points. More than 3000 photos of rocking data are modeled by CC software, and the osgb format 3D model is output. The lidar data is calculated by differential inertial navigation software, and the Las point cloud data is output by adjustment.
The following shows the three-dimensional model of the survey area and the original point cloud. We use terrasolid to classify the original point cloud. Use the classification function in terrasolid to adjust the functional parameters according to the actual situation of point cloud, and finally separate the ground points. Finally, the correct terrain point cloud is obtained through the inspection of DEM generation tool and cut plane tool in the software. For areas with large water areas and housing areas, large holes will be formed after the ground points are separated. We can fill holes and smooth point clouds in the dtmttoolkit tool in the INPHO main module.
I won’t focus on the methods of point cloud classification here. If you need to learn point cloud classification or encounter problems in point cloud classification, you can leave a message in the comment area or send a private letter to me, and I will help you at the first time.
Load the produced osgb model in EPS. Before formal production, we need to import the control point checkpoint into EPS to check the accuracy of the model, so as to avoid unnecessary rework. In EPS, surface features and some visible scarps, slopes and other landforms are drawn according to the national topographic map illustration standard of 1:500. Through the inspection of checkpoints, the horizontal accuracy of the model produced according to the resolution of 2cm fully meets the requirements of 1:500 national specifications.
The processing of landform needs to be combined with point cloud. There are two ways to generate contour lines:
One is to use the processed ground points to generate DEM and then generate contour data. Import contour lines into EPS and modify them according to 3D model and laser point cloud data.
The second is to import the ground points into EPS, select the point cloud color rendering model as user-defined display – display by elevation, select the starting point elevation as 0, and the grading height can be set as the contour distance of -0.5m or the contour distance of the calculation curve of -2.5m. Then draw contours of different elevations by hand. This method is applied to some scenes where the contour line representation is complex and the contour line cannot be well represented. Using hand drawn contour lines can better represent the terrain and landform. When drawing contours, we can lock the point cloud perspective in the vertical perspective, so that the drawn contours are not easy to intersect.
After contour processing, we can add elevation points in the point cloud, so that the elevation will be more accurate, and there will be accurate elevation points under the vegetation.
Here we will introduce a hidden function in EPS, which is the function of point cloud slice drawing and linkage drawing with three-dimensional model. This function is in EPS 6 0 has been updated and upgraded, which will be easier to use. EPS5. 0 also has this function. I also take eps5 here 0 to give you a demonstration, you can use it according to your own needs.
Open the point cloud data in the independent window of point cloud – point cloud, and you can carry out linkage drawing with the 3D model in the main window. We can set the work plane and slice the point cloud to better draw the wall of the house scanned by the laser point cloud, or draw some ground objects. While drawing, the three-dimensional model is also linked, which is convenient for us to understand the relationship between on-site features from multiple perspectives.
After the final contour lines and elevation points are completed, the original unclassified point cloud can be loaded in EPS to check whether there are missing topography; Whether the trimmed contour lines and elevation points fit together to further ensure the accuracy of topographic map accuracy.
After the work on EPS is completed, CASS format is exported, and the filling of ground objects and the modification of the whole map are carried out in CASS. After the modification, a topographic map meeting the 1:500 national standard will be deflected. In the later stage, the on-site mapping and the above drawing can be carried out according to the needs of the project.