Using Phanton 4 data then processing with Pix4D

[sashabodie]

Hey anyone having issues with using their Phantom 4 then processing the data with Pix4D and getting a vertical bust of 1m or more? Thinking of buying a more expensive UAV (eg. eBee)

 

[Javier Ruiz O]

Hi. During a couple if days inspecting with drones (Inspire, M-600) a power plant very large industrial structure, we were asked to also produce a 3D model of the site. We used a Phantom 4 to make a couple of hundred zenithal photos (setting the shooter to one image every three second) plus another 200 photos orbiting around the structure.
Pix 4D had no issues accepting the JPG photos first, and processing them later. There were some problems process time, and in some occassions we had to delete some photos to diminish the amount of data and avoid crashing.
Prior experience with P4 photos and Pix4 were well, but using less than 50 or 70 photos. We have been told that a portable PC has not enough graphic power to do these type of jobs. Ours has 16 Gb memory and a NVidia 920.

After several intents (process time of 5 to 9 hours... for each intent), we were able to create point-clouds from projects up to 490 photographs of the site, but these large projects crashed later when trying to calculate the 3D mesh. Useful finding: splitting the photos by half (selecting them down to 250 photos fron the total 500), the project worked flawlessly, and outputs were almost as good as with the totality of images.
The final results and video outputs of the mesh are astonishly superb! Two weeks ago I would not had believed it! Now the client is happy, and so us.

P.s.:
1.- We found that after the point-cloud calculation (step 2 in Pix4), there is a need to drastically reduce the terrain around the object of interest, using the editing tool and deleting surrounding areas. That fixes the computer crashes normally. And that does not delete these deleted areas frim the final processed model.

2.- After processing more than 15 project iterations we never got satisfactory results of the 3d-mesh: when it was created, the model seemed good looking but with far too many 'crazy floating points' around the structure. By chance, we found that once the mesh is created, it is compulsory to click over the mini boxes of the point-cloud and ray-cloud (left column if programme) in order to avoid seeing those points. Miraculously, all crazy points dissapear, and results appear really professional.

 

[sashabodie]

what's your vertical accuracy? I am running projects upwards of 1300 photos or more. My computer is 32 GB ram with i7 processor.

 

[Javier Ruiz O]

The accuracy of the position of each point of the model is given by the accuracy of the georeference. In the case of Phantom 4 or any other device using a standard GPS can be as bad as 10 meters. When you input georeferenced photos inthe program, the accuracy in Pix4 is shiwn as 5 meters horizontally and 10 meters (33 feet) vertically, and this is what appears in Pix4 quality reports after the calculations. But in all projects you can ammeliorate the by including some (5 to 10) better accurate points, called Control Points. If those points (fixed, showing good and small details for identification) appear in the photos, you can find their "exact" position even later than your flights, by using a field RTK GPS. In Spain, we rent it for a day or two ( cost here is about 100$ per day). The best thing is to incorporate those points in the photos taken during the flight, placing several targets (we use white crosses over black backgroung panels which are placed and fixed in several scattered places) over the terrain or buildings. Those crosses are measured with a Field, accurate GPS device, and results are annotated. After the photos are incoporated to Pix 4, and the ray cloud has been obtained, you have to give the programme the annotated good positions of this crosses, identifying them in the photos and typing the numbers. These new points, will give the whole model an accuracy of around one centimeter. There are drones with RTK GPS onboard, but the price of the sensor is higher than the Phantom4 itself!

 

[Javier Ruiz O]

Regarding the "accuracy" of the details shown in the model (called resolution) this depends of the camera lens and platform stability. These is the accuracy of the measures that can be done between pixels in the model, or the ability to identify small items in the images. In the case of Phantom 4 camera, you can expect a GSD (ground sampling distance) of 2 centimeters in features at ground level if the flights are done 50 to 60 meters AGL, and up to 10 centimeters if you fly at 120 meters.

 

[sashabodie]

Regarding the "accuracy" of the details shown in the model (called resolution) this depends of the camera lens and platform stability. These is the accuracy of the measures that can be done between pixels in the model, or the ability to identify small items in the images. In the case of Phantom 4 camera, you can expect a GSD (ground sampling distance) of 2 centimeters in features at ground level if the flights are done 50 to 60 meters AGL, and up to 10 centimeters if you fly at 120 meters.

I have GCP's in my project and I flew at 300 feet with 85% overlap. When I load into Pix4D I get a GSD of 2.7 cm but my Check Points are averaging out at 17.4 cm vertically. I have selected the target in every photo. I am just wondering if a phantom 4 is worth using for huge projects (upwards of 100 acres) or I should upgrade to a eBee? I don't know if the camera can handle that many photos (1400 photos) then when I go to process I am getting a big error. I am thinking the Phantom 4 is only good for projects under 10 acres.

 

[Ciccio]

Hi everybody can you confirm that Pix4D Capture can work with a P4A? I gave up after trying many times as it does not connect to the drone and could not even see the camera....I've finally opted for the Precision flight but I'm not very satisfied with the result..Can you advise?

 

[Javier Ruiz O]

Never used Pix4D Capture. I have made several projects flying the P4 with DJI Ground Station Pro. Programming the App is amazingly simple. I use a fixed photo interval of one every 2 seconds, both in 3D Map Area (to create orthophotos and terrain georreferenced maps) and in 3D Map POI ( to create 3D models).
The photos taken were accepted by Pix4D without any problem.