Pix4D is a useful software that can be utilized to process many images taken by UAS platforms. With this program it can put together images at a relatively quick pace (depending on size of files), and create professional looking images. With the ability to process this data it can then be brought into Esri's ArcMap or Arcmap pro to create maps that can be displayed with the relative information. The program is relatively easy to understand as well as having everything needed placed out well. Also, many questions can be answered through the help directory on the program as well as other forums found on the internet.
Some questions that should be known before using the program to generate good results:
o Look at Step 1 (before starting a project). What is the overlap needed for Pix4D to process imagery?
75% frontal overlap with 60% side overlap
o What if the user is flying over sand/snow, or uniform fields?'
85% frontal and 70% side overlap is needed for these areas.
o What is Rapid Check?
Rapid check is more used in the field to make sure everything is going correct for the map/coverage.
o Can Pix4D process multiple flights? What does the pilot need to maintain if so?
Yes, it can process multiple flights, and the pilot needs to maintain altitude.
o Can Pix4D process oblique images? What type of data do you need if so?
It can process oblique images it just needs the angle it was taken at.
o Are GCPs necessary for Pix4D? When are they highly recommended?
They are not necessary for Pix4D, but they are highly recommended when trying to reduce the noise and make the image more accurate.
o What is the quality report?
The quality report is what is created after any of the processing steps to give feed back of how each processes went. It alters to any fixes that may need to be done, and it gives the user a quick check on how the data is starting to look. It gives statistics and anything that may be needed for how good the data set is.
Methods:
There were two flight logs given (unprocessed) to be used with Pix4D to create an orthomosaic of all of the images given. The first step is to create a file/place to save all of the data sets to. For this, the best way was to create a folder names 2017monthday with a flight 1 and flight 2 folder inside that. This will help to keep the data separate and easily accessed. The next was to run a summary report on the data before doing the full data to make sure all of the data is correct and there are no errors. This can catch thing before having to wait long periods of time just to start over again. Also, when inputting the data for the DJI Phantom 3 advance the camera needed to be changed to rolling shutter.
The next step was to run the initial processed data which gives a quality report (figure 1 & 2).
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Figure 1: Summary of the first flight. |
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| Flight 2: summary of the second flight initial processing. |
Also with the report summary a coverage map is created. The areas with the most coverage will be near the middle because there will be more pictures to overlap with compared to the outside where it is on the edge with less photos to be matched up with (Figure 3&4).
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| Figure 3: Coverage map showing the most coverage being in the middle. |
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| Figure 4: Coverage is highest in the middle and lowest on the outside. |
This is import to view because it will show if there is any missing data within the area of interest along with how accurate the data will be. The more coverage the higher the amount of accuracy there will be.
Now, the next step is going be to actually run the full process. This may take some time depending on the data size. This will then generate an otheromosaic for each set of data. These can then be added into Arcmap to generate a map of the region. Figure 5 and 6 show the data that was processed in Pix4D and brought into Arcmap to be made into elevation maps.
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Figure 5: Flight 1 data after being processed in Pix4D
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This is a flyby created in Pix4D.
Results
The Flight 1 data in Figure 5 (above) has a few different patterns where there are almost roads that go between the piles of sand along with there being some type of distortion in the southern part that was mostly caused from not having enough overlap in that region or some other problem that may have occurred during the actual flight. In the second flight image (Figure 6) There is a lot of distortion on the south eastern side of the image. This is also mostly caused by not having enough images on the edge, but that is not the area that is going to be looked at for trying to solve for volumetrics, length or other processes. With both images there seems to be more detail in the center areas of the image compared to the outside.
Conclusion
Pix4D is a powerful tool for anyone looking to process aerial photographs, but if you use really bad data with not enough coverage the program will still be able to create an image, but it will not be up to standards for accuracy. It also is also a great program for figuring out the any type of 3D processes within the program. This program can be used as a great tool, but the user needs to understand the what the process is doing, and how the program calculates it to get the highest amount of accuracy.
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