GPS coordinates to pixel in image

[John_W]

Hello, I am looking for confirmation of some information. To which pixel does the GPS data in the image metadata refer to? Centre of image, corner of image?

The reply to the same question I posted on the DJI forum is that the coordinates refer to the centre of the camera.,
"It is necessary to combine position of the center of the camera + camera Heading (true North) + camera pitch. This is the reason why it is recommended to always make a dataset with images taken at nadir, then to complete if necessary with images that have an angle." I need some documentation I can give to the client to back this up.

We are using a Mavic 2 Enterprise Advanced to collect images of a solar PV installation for a company building a new software system for PV panel inspections. WE will be running the RTK unit, with an Emlid broadcasting a local/custom NTRIP stream. The Emlid will be situated on a known point at the solar installation.

 

[Meta4]

To which pixel does the GPS data in the image metadata refer to? Centre of image, corner of image?

It doesn't relate to any pixel in an image that you might take.
It comes from the drone's GPS and gives the location of the drone when the image was captured.

 

[jaja6009]

Hello, I am looking for confirmation of some information. To which pixel does the GPS data in the image metadata refer to? Centre of image, corner of image?

The reply to the same question I posted on the DJI forum is that the coordinates refer to the centre of the camera.,
"It is necessary to combine position of the center of the camera + camera Heading (true North) + camera pitch. This is the reason why it is recommended to always make a dataset with images taken at nadir, then to complete if necessary with images that have an angle." I need some documentation I can give to the client to back this up.

We are using a Mavic 2 Enterprise Advanced to collect images of a solar PV installation for a company building a new software system for PV panel inspections. WE will be running the RTK unit, with an Emlid broadcasting a local/custom NTRIP stream. The Emlid will be situated on a known point at the solar installation.

Remember one thing with the Mavic 2 EA. When using the RTK module this is for cm precision in positioning the drone only. There is NO Time Sync such as found on the Phantom 4 RTK and Mavic 3 Enterprise and you will NOT have the same accuracy in your images metadata. The coordinates and elevation in your image metadata is the same inaccurate data found in all DJI non-Enterprise/non Time Sync RTK drones.

Mavic 2 Enterprise Advanced | Drone Data Processing

Is the Mavic 2 Enterprise Advanced a good drone for Land Surveying?

www.aerotas.com

I only bring this up since it seems like you are talking about low cm precision in your needs. With the M2EA the RTK module is used to keep the drone hovering more precisely, navigating to precise coordinates for a precise inspection that is repeatable and other navigating tasks.

 

[John_W]

Remember one thing with the Mavic 2 EA. When using the RTK module this is for cm precision in positioning the drone only. There is NO Time Sync such as found on the Phantom 4 RTK and Mavic 3 Enterprise and you will NOT have the same accuracy in your images metadata. The coordinates and elevation in your image metadata is the same inaccurate data found in all DJI non-Enterprise/non Time Sync RTK drones.

Mavic 2 Enterprise Advanced | Drone Data Processing

Is the Mavic 2 Enterprise Advanced a good drone for Land Surveying?

www.aerotas.com

I only bring this up since it seems like you are talking about low cm precision in your needs. With the M2EA the RTK module is used to keep the drone hovering more precisely, navigating to precise coordinates for a precise inspection that is repeatable and other navigating tasks.

Thanks @jaja6009

 

[Mountainman75]

Remember one thing with the Mavic 2 EA. When using the RTK module this is for cm precision in positioning the drone only. There is NO Time Sync such as found on the Phantom 4 RTK and Mavic 3 Enterprise and you will NOT have the same accuracy in your images metadata. The coordinates and elevation in your image metadata is the same inaccurate data found in all DJI non-Enterprise/non Time Sync RTK drones.

Mavic 2 Enterprise Advanced | Drone Data Processing

Is the Mavic 2 Enterprise Advanced a good drone for Land Surveying?

www.aerotas.com

I only bring this up since it seems like you are talking about low cm precision in your needs. With the M2EA the RTK module is used to keep the drone hovering more precisely, navigating to precise coordinates for a precise inspection that is repeatable and other navigating tasks.

So here is a scenario: I use the M3E at 400 ft, nadir, and put a traffic cone in the centre of the image. When I look at the properties of the photo it shows the GPS location. Is that location the centre pixel in the photo or the exact location of the centre of the camera on the drone at the time the photo is taken?

Long winded explanation for the question, apologies in advance:

I conducted a test with forestry where personnel laid out several propane heat signatures located around a grid in the forest, some hidden under logs and some in the open, and recorded their exact GPS locations. We used the M300 RTK and H20T to locate the thermal signatures from 1000' (yes we had an SFOC for 1000'). I was hired as they required a certified thermal operator, I was not the drone operator or map guy. We did not use the laser locater for some reason. They compared the results of the GPS extracted from the photos to the GPS locations of the devices, and our map guy mapped them out and presented it to the coordinator. The comparisons were scored and the DSP with the highest score, or most accurate data, gets the contract. I was not part of the mapping and I really want to learn the workflow. I have an M30T now and plan to conduct the test myself. I know it's not time sync, and I could probably get very accurate data with the laser range finder. However, let's pretend I don't have the range finder and I am just using exif information or the drones location.

 

[jaja6009]

Wow, that sounds like a cool test!

For your question, this is better asked to tech support at Pix4D or Agisoft. (Agisost's Alexy comes to mind as being a very good person to ask).

I could assume an answer, but could be wrong.
There are formulas to obtain the principal point and I think Pix4D lists it for their camera models.
Older photographs with fiducial marks supposedly made finding the principal point easier in predigital days.

Sorry I cannot be much help here, but do not want to steer you off course for your work with guesses and internet research. I would find the information from a photogrammetrist or photogrammetry software expert.


Also IMO I do not think the M30T is up for this task. But let us know how it makes out.