Overview:
Lab 10 was the introduction to the Pix4d software and some of the features it has to offer. Pix4D is an image processing software that is based on finding thousands of common points between images. Pix4D uses key points to create a 3D image. Key points are points on two images that overlap and align. With a high overlap in pictures, the more key points Pix4D will find, which leads to a more accurate 3D image. The recommended overlap for quality 3D images is at least 75% frontal and 60% side overlap. Now this overlap is recommended for most cases, however small changes should be made when looking at other types of terrain. For instance when taking images of an agriculture field it would be smart to have a higher overlap due to the fact that much of the field is generally similar which makes it harder for Pix4D to find key points. When processing images of large uniform areas (water, sand, snow, fields) it is important to always use a high overlap and have the exposure settings set properly to gain as much contrast as possible. By following these quick tips it will allow for a better 3D image.
Pix4D can also process images from multiple flights. When designing your flight plans however, you need to make sure that the plan captures the images with enough overlap, along with enough overlap between the two flight plans. Also, it is smart to try to take the images from the two different flight plans under the same conditions. This will lead to better quality images. You don't want to take images one day one a clear sunny day, then the next flight you gather your images from is cold, cloudy, and raining. This wouldn't lead to good contrast between your images and you would see the difference.
One topic that always comes up with when dealing with mapping is GCP's (ground control points). Pix4D does not require GCP's for processing, but they do significantly increase the absolute accuracy of the project. In projects with geolocated images, GCP's do increase the accuracy along with placing the model at the exact position on the earth. Basically it would be smart to use GCP's whenever possible especially for projects that need high quality reports.
The final product I want to talk about when using Pix4D is your quality report. The quality report tells you about all the information that was put into the processing information of Pix4D. The report will tell the GCP's, how many images were taken and used, the coordinate system, and adding check points, along with many other features. A quality report will allow you to break down the information that was put into Pix4D to see if you can gain better optimization for your images.
Methods:
Since this was our first time using Pix4D, the process of computing the information to create our orthomosaics at first seemed to be out of this world. I was very confused but as the process went on I gained a grasp on how Pix4D worked and the ways to use it.
To begin we needed to create a new project in Pix4D. This was very simple and created it just like any other project. We went to project in the upper tab and went to create new project. This would allow us to save our projects into our lab folder for the class. Now we were ready to add our images. One thing to note however that all our images added just fine when we used the Sony SX260 camera. They were all geolocated already with orientation, meaning that all the images had the tie points already.
Figure 1
We were asked to create two different mosaics however, one with the Sony SX260 images and another with the Gems images. The Gems images however were more difficult to work with as they weren't geolocated. We had to go in and geolocate them with the export file-RGB from the Gems imagery folder.
Figure 2
After geolocating,219 out of the 220 images were properly geolocated. Although one was not located, it is still alright since there is so many images that we are dealing with. Now if we were just using say 15 images and one or two were missing, we would then have a problem.
We then went through a few pop-up screens talking about what projection we wanted and if we wanted it in meters or feet, we left these all at the default and proceed to the map. Our next screen would look like this:
Figure 3
Before continuing, under the layers box on the right hand side of the screen we turned on the GCP's and both of the processing areas. We can now click on the start box on the lower portion of the screen. Depending on how fast your computer is, how many images your processing, and the image quality, it could take from a couple minutes to compute all the data or several hours. It is all contingent. Upon the slow and painful process of waiting for the Pix4D to compute your images, you will eventually end up with an image.
Figure 4
Now the image above looks scrambled and not very pleasing to the eye. All the big green dots are were the images were taken throughout the flight plan, while the blue dots are the geolocated points since this was taken with the SX260 camera. To be able to make this image make sense you need to locate the 'Triangle Meshes' box on the left side display. Once you click on this it will compute for a few minutes and a magical image will appear that will make sense for you.
Figure 5
Now you can see an orthomosaic image that makes sense. I turned off the cameras box on the left hand side so the green and blue dots disappeared. Upon creating this image we were asked to do four more things for this lab. We needed to find the surface area of an object, volume of an object, measure the length or width of some object, and make a video animation of our image. Three of these functions are located under the measure tab on the upper portion of Pix4D, while the video animation is located right next to the measure icon. Upon creating the measurements we needed I could then export them individually and save them as a shapefile to allow me to bring them into ArcMap to create maps. Video animation was a little tricky at first, but the dialogue box that pops up when you click on the video animation button allows you to follow step by step instructions to create a video of your choosing.
Video 1
With the video being the last step that we had to complete in Pix4D, we have now completed what we wanted to accomplish in it. Our next step would to be creating maps in ArcMap showing our shapefiles that we created from the measurements and the differences between the SX260 camera and the position compared to the Gems imagery.
I created four maps in Arcmap allowing me to show the difference between the two cameras that we used. When taking the images with the SX260 camera, the camera had to be have been slightly tilted giving us an image at an angle. This didn't show up on our maps we created but I noticed it in Pix4D. The first two maps I created were from the Gems images. I created just a mosaic of the soccer fields then created another one with my measurements on the mosaic. In both my Gems maps and the SX260 maps my measurements were of the same structures. This allowed me to compare the two measurements. Although the angle was slightly different with the SX260, the measurements would remain the same.
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One difference you can see between the Gems images and the SX260 images is of the soccer field area that is pictured. The reason why there is a difference is because we used two different flight paths for either camera. We could have uploaded and used the same flight path if we so choose, but decided to create a new flight path for each camera. Roughly the same area is pictured so it's not a big deal, but if this was to compare images for a multi-million dollar project I would have used the same flight path for both of the cameras giving the exact same area pictured.
In the end this software can open the doors to much more than what was performed in this lab. Only a small section was covered on how to make orthomosaic maps and use the measuring and video animation tools. These are just the basics of the computing skills that can be done with the software. With these tools in hand now however and reading through the software manual, the possibilities are endless. From mapping tunnels, to using GCP's, and mapping standing buildings, structures, and interior, all these functions lead to endless possibilities with improving map making and reports for business while opening a vast array of new jobs.
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