Field Activity 13: Pix4D Demo

Introduction

The objective of this lab was to gain experience with the processing software known as Pix4DMapper and use some of the various tools it has. Pix4DMapper is a program that transforms aerial imagery taken by unmanned aerial vehicles (UAV) or an aircraft into one large mosaic that can be processed using 2D or 3D surface models. The use of this software along with the coupling tools (such as a UAV) has been proven to be a cost effective way for companies to analyze their land and produce high resolution imagery to back up their work. For example, sand mining companies can use the software to calculate the amount of sand extracted from the ground in a given day by using the volume tool within the program. The lab focused on a mining site located just southwest of the University of Wisconsin- Eau Claire (Figure 1). The aerial imagery was captured using a Phantom drone provided by the university.

Figure 1: The location of the mining site in Eau Claire

Background

Prior to beginning the lab, it is important to do some research on the software and understand its capabilities and data parameters. The following questions were answered using the online Pix4D Software Manual. 

• What is the overlap needed for Pix4D to process imagery?
• Overlap refers to the overlap of the various images that will be tied together into one image (termed mosaic). In most cases, the overlap needed is roughly 75% frontal overlap and 60% side overlap . 
• It is also recommended that the area of interest be captured in a grid patterned flight (Figure 2) in order to ensure proper overlap. 

  

  Figure 2: Recommended flight path to create the best overlap for mosaic
   (Pix4D Software Manual 2016)

• What if the user is flying over sand/snow, or uniform fields?
• 85% frontal overlap and at least 70% side overlap.
• Also recommended to fly higher for better results

• What is Rapid Check?
• Processing template that creates output imagery faster but with lower accuracy. 
• Reduces the resolution of the original images
• Fewer keypoints are used on each image 

• Can Pix4D process multiple flights? What does the pilot need to maintain if so?
• Pix4Dmapper can process images taken from multiple flights as long as....
• Adequate overlap is achieved
• Same conditions (sun direction, weather conditions, no new buildings, etc.) are present during data acquisition.

• Can Pix4D process oblique images? What type of data do you need if so?
• Pix4D can process oblique images if.....
• Enough overlap in each dataset and between datasets. 

• Are GCPs necessary for Pix4D? When are they highly recommended?
• No, they are not necessary but are useful to have. They are highly recommended during tunnel reconstruction

• What is the quality report?
• Processing report that identifies any errors with the data imagery.

Methods

To begin, the data was pasted into a personal folder. The image data was then uploaded into a new Pix4D project. From this point, the processing option had to be chosen. The one used was the 3D map. This allowed for a digital elevation model (DEM) and orthophotos to be created. After a mosaic was created, the area of interest had to be created. To save time, a small section of the mine was selected because the processing within the software takes a lot of time (Figure 3).  

Figure 3: the area of interest outlined in red was established to provide fast processing

The next step was to begin the processing of the AOI imagery. There are a total of 3 processing stages. Beginning with initial processing which allows user to change processing options and select the information to be put into the quality report. The quality report was looked at following this step (Figure 4). Based on this report, there was a 30% difference when it came to camera parameters and small issue between the ground control points. 

Figure 4: The quality report from the initial processing step. 

The next processing step was a point cloud mesh and DSM processing feature. This creates a 3D image of the data that can be seen in the results. the next steps were to use the various tools within the software. To begin, the volume tool allows one to calculate the volume of a material in a mound. In this case, the mound was made of frac sand. The volume was calculated by manually enclosing the pile of frac sand (Figure 5).The results are then calulated using the various pixel information within the specified area (Figure 6). Next, the DEM results were explored with different variations to show the data (Figure 7-8). The colored DEM was selected to how the differences in elevation more clearly.

Results

Volume:

                           

                       Figure 5: The study area with the pile of frac sand being calculated located in the lower right of the image.

 

Figure 6: The results from the 

DEM: 

Figure 7: The results from the study area DEM. The high points are shown in red and the low in blue. 

Figure 8: The total mosaic of the data prior to DEM compared to after DEM creation. 

Discussion/Conclusion:

The results from the Pix4D software shows the large amount of tools and capabilities that the software has to offer. though this lab was meant to just be a preview of its large amount of capabilities, it is clear that the software can be applied to many different fields such as business, environmental sustainability, and agriculture.