Vertical shift between flight blocks /EXIF file. I'm lost!!

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

hi,

i use drone P4P for 1km2 mapping

i have 30 mission(flight)

i use 5 GCP’s.

I use the same GSPs coordinate system (WGS84).

i make good over lapping between flights.

i fly 40m altitude 1GSD.

i follow the right workflow as per your instruction of website which:

1- run initial step for each mission separably. (here i check quantity report, i have 1 block created for each mission).

2-marge the sub project in one project. (here i check quantity report, i have 8  block created for each mission and virtual shifting around 50m).

3- Mark GCPs.

4-Re-optimize (here i check quantity report, Its same i have 8 block created for the project).

This is the first result !

 

i try something different as following:

 

1- run initial step for each mission separably. (here i check quantity report, i have 1 block created for each mission).

2- add MTPs for sub project and reoptimize 

3-marge the sub project number 1 to sub project number 2 in one project . (here i check quantity report, i have 1 block created )

4- add MTPs for merged project 1+2 & reoptmize.

5-then i marge sub project number 1+2 to sub project number 3 , and 1+2+3 to 4 all by using MTPs…So that for 30 mission 

6- I Mark the GCPs.(here i check quantity report, i have 1 block created )

7-Re-optimize (here i check quantity report, Its same i have 1 block for the project).

This is the second result ! but it take long long time !! (Where I tried to put MTPs on each optimized sub project and marge them one time but still i have multi blocks.  

 

after asking some Pix4d users they said

" if you using GCPs remove the geolocation from the photo because the initial geolocation on the photos is highly inaccurate in comparison to the GCPs, the mismatch in between the blocks should be corrected once your remove  the EXIF file data from image, So the correct workflow will be as follows :" 

1.do your initial processing with the geolocation on.
2. Mark gcps
3. Remove exif data
4. Reoptimize
5. Check for accuracy
6. Continue to process next steps

The quote ended.

Now i do not understand that and i don’t know how to do that and i don’t if that is the right workflow. what you say about that.

and kindly inform me if there and setting i should do on my drone P4P before starting the mission, because i do nothing only run pix4d mapper and change the mapper software setting it self.

 

Thanks

2

Hi Raed,

I’m sorry to hear that you’ve run into a hurdle merging your projects.  The geotag location from DJI drones should have good values for the X & Y coordinates, however the Z value isn’t based on GPS reading, but height above take off (perhaps from Barometric reading) and this can lead to different Z values over multiple projects.  Review of your workflow sounds pretty good, however I do have a few questions.

Are you using consistent/Unique names for all the GCP & MTP points you are creating?  By default Pix4D will name them GCP1 or MTP2 etc, however If you don’t create the points in the same order in different proejcts, they can have “different/non consistent” names across subprojects.  I like making unique names for each GCP/MTP so I know they are consistent across all subprojects.  You should be able to merge multiple projects together simultaneously (i.e. run all 30 projects through step 1, then create a 31st project that is made up of the 30 projects done through Step 1 that can be run through steps 2 & 3 as 1 BIG project.

Once Step 1 is done, I would suggest using the GCP/MTP Basic editor to mark atleast 3 GCP in each sub project (if possible) along with any other MTP, then reoptimize prior to Merging the various subprojects. If you attempt to merge projects prior to them being Reoptimized, they will invariably merge together as seperate blocks.  Mark GCP/MTP then Reoptimize prior to merging.  

Please let submit a support ticket to Pix4D if you continue to experience issues merging.

1 Like
3

The easiest fix is to overlap the missions by one or two passes of the drone.  I took 12 flight missions and combined them into one project without a single GCP or MTP simply because I overlapped my mission plan independent of my side overlap %.  The world of photogrammetry is all about the overlap to make processing easier with less human labor hours thus less cost.

My project was with a DJI M600 and DSLR camera with geotagging post-flight so the coords were not perfect by any means.

Fixing something like this after it is flown is very difficult and we all here have had mixed results trying to use MTPs to merge multiple projects…if the overlap is low then no number of MTPs will merge it, from my experience.

2 Likes
4

So true Adam!

More art than science.

5

Dear Mr Aaron,

with regard your question :

“Are you using consistent/Unique names for all the GCP & MTP points you are creating?” yes I use same MTPs name for the same point in both of overlapped projects.

“however the Z value isn’t based on GPS reading, but height above take off (perhaps from Barometric reading) and this can lead to different Z values over multiple projects”

is that happened in all project has multiple flight for big area? even the over lapping applied at site between missions??

 

Now this project merged success by second option as what I descript in my question above where take long time, I am not planning to re-work on this project again by testing what you explain form me.

All my concerned now is how can I avoid the vertical shifting and got 1 block for my merged projects incoming huge projects, what I want is finishing the initial processing without using MTPs, I don’t want to waste time by stitching the shifted block by MTPs.

So if there is conventional workflow or settings or means ensures that please tell me starting from the site (by using P4P) to finish the initial processing on the PC at office.

Kind regards, 

 

 

 

 

6

Dear Adam Jordan, 

But I do apply overlapping between missions by 1 and some mission with 2 passes of the drone! what is the right overlap percentage for a project with 30 missions and its area 1 km2 and 40m fly altitude (1GSD)?

Do you suggest increase the overlapping due to the low drone mapping altitude?

 

Kind Regards,

7

Well each project is different but all I can say is that with enough overlap then you don’t need MTPs to bring the separate missions into 1 block. As I said before, I moved my mission plan to overlap 1-2 passes of the drone for each battery change. I mainly did this because at the time there was no change battery resume feature like there is now. The side benefit of those 12 flights was not needing any MTPs to process as 1 project resulting in 1 block…of course not every computer can handle the gigapixels, which was over 210 in this project.

As Gary said, this is an art more than simple button pushing and using default setups. Simple trial and error is how I figured most of this out. Best help I can give is to max out the overlap and picture count for your hardware and see if it meets the customer requirements for deliverables.

1 Like
8

Adam Jordan 

Thank you , Actually what is confuse me when some one said to me  :

" if you using GCPs remove the geolocation from the photo because the initial geolocation on the photos is highly inaccurate in comparison to the GCPs, the mismatch in between the blocks should be corrected once your remove  the EXIF file data from image,

make me think I should do that every project as conventional workflow!

9

I have never heard that and I would never remove EXIF data. I have seen Pix4D fix wrong GPS coords by 1000 feet so I don’t believe that statement your heard.