UAS Data Processing with Pix4D

Introduction:

Pix4D is an incredible program that allows the user to to convert aerial images taken by unmanned aerial surveillance vehicles into georeferenced 2D, and 3D surface models, point clouds, DEM, orthomosaics, and many more options.  It has many uses which include being used in agriculture, the mining industry, construction, and almost any other place as well. This program can create amazing models if done with the correct accuracy.

Pix4D Questions:

• What is the overlap needed for Pix4D to process imagery?

The recommended overlap for the user is at least 75% front lap and 60% sidelap.

• What if the user is flying over sand/snow, or uniform fields?

In an area with sand/snow 85% frontlap and 70% sidelap is needed.

• What is Rapid Check?

It is a quick processing that creates a visual surface of the area, but it will have a low resolution.  

• Can Pix4D process multiple flights? What does the pilot need to maintain if so?

Pix4D can process multiple flights and the pilot only needs to maintain the same vertical and horizontal coordinate system throughout the multiple flights. 

• Can Pix4D process oblique images? What type of data do you need if so?

Pix4D can process oblique images, but it is recommend to take images every 5-10 degrees.  It is also recommend to capture two sets of data at different heights. 

• Are GCPs necessary for Pix4D? When are they highly recommended?

They are not necessary for Pix4D, but they are highly recommend when there is no geolocation.  

• What is the quality report?

The Quality report produces a description with information informing the user how the initial processing looks. It gives a summary of all the checks of the data during the initial report and a low quality picture of the area.

Methods

To start creating surface models in Pix4D start with a new project named something that follows a naming scheme and save it in the correct folder.  Next, the select images screen will open which allows the images taken with the drone to be selected.  Find the correct folder containing the images and select them all to be processed.  Click next and and review the image properties.  With the drone used for our images the shutter mode needs to be changed to linear rolling.  Click next, to review the output coordinate system, click next to select the processing type.  For this case it will be "AG RGB."  To make the processing faster it may be useful to create an area of interest.  This is done by selecting map view and then selecting processing area.  Now click and draw a figure around the area intended and finish with a left click. Now to run only use the initial processing first to make sure the data is all good to go.  Finally, run the next two processes next to the initial processing to create the 3D surface model.

Calculate Surface Area

• Select View
• Select Ray Cloud
• Select New Surface
• Left click to make area and Right click to finish. 

Figure 1: Surface area. 

Measure the Length of a linear feature

• Select View
• Select Ray Cloud
• Select new PolyLine
• Click to select distance to be measure

Figure 2: Linear Distance

Calculate the Volume of a 3D object

• Select View
• Select Volume
• Click New Volume
• Draw out the points around the part of the image and right click to finish the shape. 

Figure 3: Volumetric calculation.

Create an Animation that 'flys' through the project

• Select View
• Select Ray Cloud
• click on the camera icon from the create box
• Choose generated waypoints or computer generated waypoints
• choose the duration and speed of the flight
• save the file

Results

Figure 1: DSM of the area of interest of the mine in Litchfield. 

Review

Pix4D seems to be a relatively easy program to use with everything layed out well on the main screen.  Even a beginner could pick up this program and upload the images and start making material with the help of other internet sources.  Its great that this program creates high quality data without having to have relatively high quality data to start with.  Although, this can be dangerous to some this is a wonderful program to work with.  It may not be as accurate and speedy as LiDAR, moreover it is still a wonderful tool if only aerial photo are available.  This program has many uses, it can be used in consulting for environmental firms, real estate, or even just taking aerial photographs as a hobby. overall this is a great program to use.