Processing DJI Phantom 4 RTK datasets with PIX4Dmapper

Hi Blaz

With Phantom 4 RTK, I did 3 sub flights to cover a huge area yesterday by swapping battery twice in the middle, and got 3 different folders of images in the end.

Is there any way to create one folder from these 3 folders of images?

Do you have any suggestions regarding the image processing?

BTW, I flied with 2D photogrammetry mode in order to measure volumes of stockpile.

In addition, when I loaded the images of 3 folders all together to a project in Pix4D Mapper, there is no satellite or google map background shown. Anything is wrong? if so, how to fix it?

Thank you in advance.

Cindy

Hi @cindy.wang,

  1. Basemaps not displaying

Pix4D software uses Mapbox as a basemap provider. Mapbox will shut down its Legacy Static tiles API 9 as of November 1st, 2020. Hence, the current and previous version, which uses the older API will have issues with the basemap. More in the Mapbox basemap issue with older versions of Pix4D’s software community post.

The best solution is to update the software to the latest version (4.6.3) here.

  1. Image folders

If the image names are unique, then you can simply copy them into one folder and process the project as per normal. Even if you keep images in separate folders and import them for processing it should work fine.

As a side note, we developed a new desktop application Pix4Dmatic that is optimized for large scale projects. It is designed to handle and process thousands of images with ease while maintaining survey-grade accuracy.

Feel free to download it and try it out.

Best,

I am confused by what should be used for Vertical System in Pix4D. We are using DJI Phantom 4 RTK that is getting NTRIP data from Trimble VRS Network. Our GCP are collected with Trimble R12 GPS and that can be configured to Geoid 12A or 12B or Geoid 18. It is our company policy to collect with the most current GEOID 18. Horizontal is NAD83(2011) / Illinois East (ftUs). The first project I processed was I used NAD83(2011) / Illinois East (ftUs) for Horizontal and did nothing for vertical and my Dense point cloud was 100ish feet off from my GPS(12A) RTK12 GCP. I reprocessed, selecting a vertical coordinate system - MSL - EGM 2008 Geoid. According to this thread that I was directed to by Pix4D support, I should be finding a shift difference to apply from Geoids -12A, 12B or 18. Is this correct? It looks like my only choice in Pi4Dis Geoid Height Above GRS 1980 Ellipsoid(ft.) then adding a shift factor. This doesn’t see consistent with the Pix4D thread, "Processing DJI Phantom 4RTK data sets with Pix4D. We are Surveyors and thus looking for the most accurate horizontal and vertical, please advise.

1 Like

Hi @flynow, the 100ft offset could indeed be related to wrongly selected vertical coordinate systems.

If I understand correctly you should use the following combination of vertical coordinate systems:

  • Images: In most cases, the RTK image geotags have the Z coordinate measured based on the ellipsoid. If this is also the case for you, then you should use the WGS84 ellipsoid. This means that you use Geoid Height Above ellipsoid WGS84 = 0 in Pix4Dmapper.
  • GCPs: Let’s say that your GCPs are measured in NAD83(2011) / Illinois East (ftUs) and Geoid12B. There is no direct way to select the Geoid12B in Pix4Dmapper, but you can define it by providing the offset between the ellipsoid of the selected horizontal coordinate system and the desired geoid. In your case, you should get the difference between GRS80 ellipsoid and Geoid12B for the location of the project. For example, if the difference between those two systems is 105.052 ftUS, then use this values for the Geoid Height Above ellipsoid GRS80 (ftUS) = 105.052 in Pix4Dmapper.

Another thing you can try is using Pix4Dmatic. It supports the import of DJI Phantom 4 RTK imagery as well as the GCPs in Geoid12A, Geoid12b and Geoid18. You can find more information and the full list of supported Geoid models in the How to use vertical coordinate systems and geoids in Pix4Dmatic article.

I hope this helps,

Dear Pix4D,
I have used this method (ellipsoid to Geoid +), to processes the images from Phantom 4 RTK, no GCP used, as a test flight, to test the RTK only method. The point cloud after running all steps, seams to be correct, or very close, but the ground control points, which I was going to use as check points, are displayed with incorrect elevations, and Pix4D does not let me do the QC. I typically process everything with GCP’s, but this is a test flight of my base+ phantom RTK setup, and I wanted to see what I can do with it. Can you think of a reason the GCP are displayed with the incorrect altitude? It is actually 2 times the difference of Geoid to ellipsoid.