Introduction
Pix4D is a suite of photogrammetry software designed specifically for UAS mapping. In this exercise I used it to make a "video animation trajectory creation" (aka: a fly through video) and generate GeoTIFF files which can be imported as layers in ArcGIS for further analysis. Made specifically for UAS applications, Pix4D is a great tool for processing and viewing UAS data and producing many of the deliverables clients are looking for.Methodology
This exercise is meant to serve as an introduction to processing UAS data in Pix4D. Sometimes this data may take a very long time to process which is why we only used a subset of the Wolfpaving UAS data from the previous post. As shown in Figure 4.1, when importing the data to Pix4D I make sure it displays the correct properties and is using the correct coordinate system as the metadata specifies. Usually this occurs automatically, but if for some reason it does not, the data set will be unable to be georeferenced.
Figure 4.2 illustrates the flight pattern the UAS flew for the mission. In order to see if enough valid data was collected to produce accurate maps, Pix4D allows initial processing of the data (figure 4.3) which will then spit out some quality reports to be analyzed. One major setting that needs to be changed in this wizard is the camera shutter type. Many cameras including the one used in this project have a rolling shutter which moves over time and can distort the image. Pix4D can get rid of a lot of this distortion, but it must be specified prior to initial processing. The default is global shutter/fast readout which would be better to fly but can often be more expensive. Figure 4.4 shows the summary of this initial processing. One thing to note is that the average ground sampling distance is 2.35 cm which indicates that this data set will be very precise. Figure 4.5 displays the overlap strength. From this map you can see what areas have high levels of overlap (center and along flight path) and which could use more data (edges). This tool may be able to help in situations where not enough data is collected and processing will take a long time. In that case, going out to get the data again may be more beneficial. The quality check verifies that that dataset will produce a good enough output to proceed. The result of this initial processing can be viewed in Figure 4.7.
If the quality report checks out, the next step is to process a point cloud and mesh along with a DSM orthomosaic and index analysis. The first iteration of this can be seen in figure 4.8. Looking around at figure 4.8, however, there are many gaps seen in the data. In order to get a much cleaner image for figure 4.10, the triangulation is calculated and added. This process interpolates what the missing space should be, but it is not always completely accurate and tends to underestimate the terrain.
Once the terrain looked smooth and good it was time to make a video for the theoretical client! Using the "video animation trajectory creation" tool that Pix4D provides (figure 4.11), I was able to make a fly through of the area. Such videos may be valuable in certain circumstances where the land needs to be shown off for planning, real estate, or development purpose. The final product is shown in the section below.
Figure 4.2 illustrates the flight pattern the UAS flew for the mission. In order to see if enough valid data was collected to produce accurate maps, Pix4D allows initial processing of the data (figure 4.3) which will then spit out some quality reports to be analyzed. One major setting that needs to be changed in this wizard is the camera shutter type. Many cameras including the one used in this project have a rolling shutter which moves over time and can distort the image. Pix4D can get rid of a lot of this distortion, but it must be specified prior to initial processing. The default is global shutter/fast readout which would be better to fly but can often be more expensive. Figure 4.4 shows the summary of this initial processing. One thing to note is that the average ground sampling distance is 2.35 cm which indicates that this data set will be very precise. Figure 4.5 displays the overlap strength. From this map you can see what areas have high levels of overlap (center and along flight path) and which could use more data (edges). This tool may be able to help in situations where not enough data is collected and processing will take a long time. In that case, going out to get the data again may be more beneficial. The quality check verifies that that dataset will produce a good enough output to proceed. The result of this initial processing can be viewed in Figure 4.7.
If the quality report checks out, the next step is to process a point cloud and mesh along with a DSM orthomosaic and index analysis. The first iteration of this can be seen in figure 4.8. Looking around at figure 4.8, however, there are many gaps seen in the data. In order to get a much cleaner image for figure 4.10, the triangulation is calculated and added. This process interpolates what the missing space should be, but it is not always completely accurate and tends to underestimate the terrain.
Once the terrain looked smooth and good it was time to make a video for the theoretical client! Using the "video animation trajectory creation" tool that Pix4D provides (figure 4.11), I was able to make a fly through of the area. Such videos may be valuable in certain circumstances where the land needs to be shown off for planning, real estate, or development purpose. The final product is shown in the section below.
Figure 4.1: Importing the data to Pix4D and
verifying it is correct.
Figure 4.2: Viewing the flight path of the mission.
Figure 4.3: Preparing for the initial processing.
Figure 4.4: Quality report - summary.
Figure 4.5: Quality report - overlap overview.
Figure 4.6: Quality report - quality check.
Figure 4.7: Initial processing with camera layer.
Figure 4.8: Point cloud, mesh, DSM orthomosaic,
and index processing.
Figure 4.9: Exploring the default DSM.
Figure 4.10: DSM after triangulation applied.
Figure 4.11: Setting up the video animation trajectory
creation (fly through).
creation (fly through).
Results
Taking a closer look at the terrain produced by Pix4D, especially during the fly through, the piles of raw materials looked very smooth and accurate shape-wise. In some locations it can look too smooth. Other than the piles though, smaller and skinnier objects did not fare well. There was a tractor originally pictured (lower right of figure 4.9), but in the final rendering you cannot even depict what was once there. This type of processing seems to be made more for constructing the landscape as a whole and less of individual, small objects. With the right, I think some of this could be improved.
One of the big differences between this data processing and the previous week's exercise in ArcGIS is that the ArcGIS data utilized ground control points. Therefore, when the DSM in ArcGIS is overlaid on the terrain it appears at the proper height. When this happens with the Pix4D DSM it floats a bit because the altitude is not georeferenced to the ground points.
The fly through that Pix4D offers is a unique and fun deliverable. I enjoyed getting to use it but it was quite difficult to get the hang of. Despite having the technical knowledge to use it, it still requires a fair bit of skill. As seen in figure 4.12, the final result it mainly smooth save for a few transitions.
One of the big differences between this data processing and the previous week's exercise in ArcGIS is that the ArcGIS data utilized ground control points. Therefore, when the DSM in ArcGIS is overlaid on the terrain it appears at the proper height. When this happens with the Pix4D DSM it floats a bit because the altitude is not georeferenced to the ground points.
The fly through that Pix4D offers is a unique and fun deliverable. I enjoyed getting to use it but it was quite difficult to get the hang of. Despite having the technical knowledge to use it, it still requires a fair bit of skill. As seen in figure 4.12, the final result it mainly smooth save for a few transitions.
Figure 4.12: Wolfpaving fly through.
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