How to do earthwork calculations by ppk drone photography?

   How to do earthwork calculations by ppk drone photography?

Ground excavation projects are almost involved in earthwork calculations. The amount of earth stone is determined by the quality of terrain expression.Through drone with load GOLD F2 GPS PPK Kit, It generated topographic expression, small workload, high software automation, reliable calculation accuracy, and calculation results are subject to survey methods and calculation methods. Its results are used in the calculation of equivalents in two flops, and the results are reliable and have visual effects.

1.Earthwork calculation method with high accuracy PPK Drone photography survey

1. 1 PPK Drone photography survey technology

The photographic survey can obtain a high-degree and high resolution digital surface model DSM, which fully expresses the ponor of the terrain, simultaneously output positive photographic image data with spatial position information. It can be measured in image data. The drone is equipped with the PPK kit,  will have featuress like accurate actions, flexible, fast, economy, etc.,  UAV PPK can quickly& efficiently obtain high-precision high quality, high resolution images.

Photography survey techniques typically include key content such as image pretreatment, regional network combination, multi-view matching, DSM generation, real incident correction, three-dimensional modeling.

Multi-view combination. Multi-view images not only contain vertical photographic data, but also inclined photographic data,combined with the multi-view external position elements provided by the GOLD PPK cm POS system, the same name automatic matching and free web beam method is performed on the image.Better matching result is obtained.

Multi-view image intensive matching. Image match is one of the basic problems of photographic survey. Therefore, how to fully consider redundant information during the matching process, quickly and accurately obtain the same name coordinates on the multi-view image, and then obtain the three-dimensional information of the ground object, which is the key to multi-channel image matching.

Digital surface model generation and true misconduct image correction.Multi-view intensive matching can obtain high-accuracy high resolution digital surface model (DSM), which fully express the ponor of terrain substrates. But there are large scale difference in the multi-angle tilt images and serious occlusion and shadows,  the new difficulty is automatic getting DSM if based on inclined images

1.2 Workflow for PPK Drone photography survey

1.2. 1 Data acquisition

Synchronous collection surface image and high accuracy POS by using DJI phantom 4 pro with GOLD F2 PPK Kit.

1.2.2 Data processing

Match the geometric image to get sparse point cloud.Through the corresponding algorithm, the sparse point cloud is encrypted to obtain a dense point cloud, and the dense point cloud is grown and textured to obtain a 3D model.

1.2.3 Output

3D Model to 4D product

Photoscan can fully automated processing data,making 3D model equipped with detailed coordinate by awarded real control point. And based on the high accuracy real 3D model, it can generate the survey results  such as DSM, DOM, DLG, etc. See as following operation steps in Figure 1.

1.3  Earthwork calculation by DEM

The key to earthwork calculation is to accurately express the original terrain landform and post-excavation.Through function spatial analysis and superposition analysis which  based on DEM,ARCGIS can analyze topographic model before and after excavation, ARCGIS can give final filling earthwork quantity by calculateing the volume of the pad through its statistical analysis module.

The ArcGIS software calculates earthwork equivalent by using raster data. The raster data structure is simple, very beneficial to computer operation and processing, is a space base data format which GIS commonly used. Spatial analysis based on raster data is the basis for GIS spatial analysis. The ArcGIS Grid Data Space (Analysis Module) provides a valid toolset that is convenient for performing the calculation of the floor equity. By tilting photographic survey, the pre-surface data and later surface data gridization data are obtained, and the two grid data is calculated, and the difference is the filling (excavation) height of the grid point.

1. 3.1 Data preparation

Prepare excavation DEM and post-excavation DEM by tilt photography survey, or DEM generated by design data

1. 3. 2 Data processing

Check the consistency of  data coordinate system to ensure that two data has the same coordinate system and elevation system,  coordinate system should be a Gaussian projection plane coordinate system

1. 3. 3 Earthwork calculation

Calculate the floor with 3D Analyst Tools → Raster Surface → Filler Tools. Figure 2 is selected in the dialog window to enter the two DEM data, and the output grid is the DEM data storage location within the final extracted excavation or backfilling range.

Figure 2  Dialog about ArcGIS Filling Tool

1.3. 4 Earthwork statistics

According to the final DEM data from extracted excavation or backfilling range,  ArcGIS can be statistical quantity of filler square by its statistics function.

Earthwork calculation case about Drone PPK in tilt photography survey

Taking a open-air mine as an example, it is required to calculate the amount of mining period. Using DJI drones equipped with PPK as a data acquisition platform to obtain two DEM data, ArcGIS software calculates its earthwork, and results are compared with the actual survey data.

2.1 Data preparation

Aerial photo data is obtained by route planning,ground control point

survey, aerial photography, etc. By align photos, establish a dense point, generating a grid and other processes to export DEM data by using Photoscan software.

2.2 Earthwork calculation and data statistics

Calculate earthwork with 3D Analyst Tools → Raster Surface → Filler Tools. The output grid is the DEM within the final extracted excavation or backfilling range. Fill in the excavation area with different color tags.

2.3 Earthwork calculation for 3D visualization

With DEM data, 3D display is performed in ArcScene, which is directly reflected in the position of the plunger, and provides an intuitive change effect. As shown in Figure 6. The three-dimensional surface model (DSM) can be obtained in ArcScene by superimposed orthophoto quadrangle data and DEM data.which in the model, can query any point of coordinates, elevation, slope angle, slope direction, and other related terrain information. As shown in Figure 7.

Figure 7 3D display and any point query display

3.4 Comparison of survey results

Comparison by RTK survey data calculation and tilt survey data,difference ratio about excavation is 0. 04,which is basically consistent with RTK survey. Difference ratio for fill square is large, and its mainly reason is caused by survey errors. The theory of open-air mine mining should be excavated, and the filling should be zero.The resulting filling data obtained by the calculation results should be caused by the measurement error. Due to the presence of measurement errors, two measurement data is different from the results of the same topography. Therefore, the difference between the fill square in this example has no reference significance. The calculation method of the difference ratio is as follows:

Ending

The solution about GOLD PPK drone combined with ArcGIS software to calculate earthwork, accuracy is reliable,external workload is small, the degree of internal automation is high.  it can not only offer 3D display but also can do implementation, query and other functions