Assignment 4: Introduction to Pix4D

Introduction
     The purpose of this assignment is introduce the Pix4D software. This software is used to process unmaned aerial systems data (UAS). This software allows for the processing of point clouds and allows for 3D volume analysis. In order to use  Pix4D, it is very important that the user has high quality data sets. This can incude the use of ground control points (GCPs), geolocation and quality imagery.
     When using using Pix4D it is very important that the UAS data has overlap. It is recommended that a there is a minimum of 75% percent of frontal and 65% of lateral overlap for most situations. If the UAS is flying over over surfaces such as snow and or sand, there needs to be increased overlap for the images. In these cases, it is recommended that the overlap should be increased to 85% frontal and 70% lateral. Pix4D is also capable of producing oblique images, if there is sufficient overlap between the images. Images that were taken over the course of multiple flights can also be processed. This is as long as the total images is below 2000 images. If using images taken from multiple flights, similar flight conditions are desired and overlap between images is very important.
     Rapid Check is also a very important function in Pix4D. This function is used to determine if there is sufficient coverage for the images in the data set. It performs this function quickly by reducing the size of the pixels in the images so that processing speed can increased.
     As mentioned above, Pix4D can use GCPs. While this is not required, it is recommended. Having accurate GCPs aids the quality and accuracy of the overlap between images. GCPs also helpful for other tasks such as processing images without geolocation as well as georeferencing.
     Once an image has been processed the software produces a quality report that contains information on the accuracy of the data collection.

Demostration 
Volume Calculations 
    Pix4D has the ability to calculate volumes of 3D surfaces. This can be done by using the volume tool found in the menu. Once the tool is selected, control points can be placed on the processed image. Once the desired control points have been placed on the image, by simply right-clicking the mouse, the volume can be calculated. This can be seen below, where the volume for 3 gravel pits were calculated using this tool (fig. 1).
    

Figure 1. Three volumes collected using the volume tool

Flyover
     Pix4D can also create animations for data sets. For this example a video was created that "flew" above the processed image. This was done by using the video tool where way points can be placed around the image. This effectively creates a flight path for the animation. Once the video's way-points are collected, the video can be rendered into video formats such mp4 for exportation.

ArcMap
    Data processed in Pix4D can also be brought into ArcMap. For this lab, two maps were created, a digital surface model (DSM) (fig.2 )and orthomosic image (fig, 3). The images for this lab were preprocessed by Dr. Hupy. The DSM and orthomosic images were brought into ArcMap as raster features. For the DSM, a hillshade was created to create better depth in the image using the hillshade tool. Once the hillshade layer was created the DSM was placed over the hillshade and was made 30% percent transparent. The DSM was also imported in ArcScene to create a 3D model. These can be seen in the upper right of two maps.

Figure 2. Displays the DSM brought into ArcMap

Figure 3. Displays the orthomosiac image

Conclusion
      Pix4D is a very effective software for processing UAS images and data sets. When processing UAS data it is important to follow the recommended overlap percentages so that the data can be processed accurately. The software provides many useful tools for calculating volumes, displaying animations, and creation of data that be used in mapping software such as ArcMap.