Pix4DMapper: Processing UAS Data

Introduction:

For this weeks lab our task is to create a orthomosaic image using Pix4Dmapper, this is a program used by geographers to create accurate 3D imaged maps. This makes the data very easy to read and very easy to analyze. The task at hand is to use this program and the UAS data provided to create a map of the study area and calculate different aspects of that study area.

Using Pix4D:

The most important thing to do when using Pix4D is to make sure the images are overlapping, when I say overlapping I don't mean a small amount of overlap, rather the higher the overlap the more accurate of a 3D model may be created. The reason why overlaps are so important when using this specific program is because it makes the 3D image more accurate and sharper than normal 3D images through the use of aerial triangulation(AT). The main goal of aerial triangulation is to determine the position and orientation of the images collected using UAS, this allows the AT to pierce through multiple images that are overlapping and create a legible map of the study area. In some cases aerial photographs may not capture as much information as needed, this is when the terrain is covered with either snow or sand. With these terrain types the overlap rates are much higher, with both snow and sand, this is because of how reflective these substances are and show minimal visual content, this is why there needs to be a certain amount of frontal and side overlap. The minimum levels of overlap for sand and snow are 85% frontal and 70% side overlap, these are minimal requirements meaning that these are the lowest values they can achieve for the images to be captured correctly. There is also another feature in which the data can be verified by the program, this is called rapid check. Rapid check is where all of the data is processes very quickly, the disadvantage to this method is that the results have low accuracy since all of the data was processes at a quick rate rather than being thorough. There are also a few more positives to using this program, for one Pix4D can process multiple flights at once, but only if certain requirements are met, the main one is that the coordinate system for all the images are the same. Another positive is that Oblique images may be processes through the use of this program, but only if the overlaps are of good quality and GCPs are present. GCPs are important but will not be used during this project, but they are a good option because when used they provide the results with more accurate findings. All of the results are presented in the quality report, this report is where all of the data is analyzed and all the figures are created.

Results:

The data that the class was provided with was UAS imagery data collected by Professor Josheph Hupy, the study area is a sand mine that is located in the south region of Eau Claire. To start off the  project all of the images were imported to Pix4DMapper, this is where the area of interest was chosen. The AOI was selected directly over the sand mine, the next step is to process the images and wait for the quality report to be generated. The creation of the quality report took about 15 minutes and the results were quite interesting. Below are figures 1 - 3from the quality report representing the information put into the report as well as maps showing the study area in different ways.

Figure 1: The quality report from the overlapping images being processed and analyzed

Figure 2: Represents both the Orthomosaic and DSM processed from the overlapping images

Figure 3: Represents the where in the study area there were strong overlapping between the images and weak overlapping

The areas in green represent the areas where there were multiple overlaps between the images making the results for that area very accurate and easy to read. While the yellow and red areas represent areas that contain poor overlap between images. Most of the areas that contain poor overlap are on the edges of the map, but the main point taken from the figure 3 is that as long the study area is showing strong overlap between the images than there will be positive results.

Conclusion:

Overall this was a very enjoyable and informative lab, learning and using a new program to create and analyze 3D images is expanding my knowledge on how to create legible and accurate maps. Pix4D is overall is a very user friendly program, making is easy to use for first timers. As well as one of the higher forms of technology for creating high quality results. This course has taught me a lot throughout the semester and I feel that ending on learning how to use a new program such as this is the perfect way to complete the course.