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Drone Mapping with Leica RTK GPS Base Station + Rover | Help

leeguam

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I recently got into drone mapping and invested a great deal in all the equipment needed. The gear I'm using is the Phantom 4 Pro V2 with the Leica GS18T rover with a base station and have some landing pad GCPs.

In short, everything went smoothly until I imported the GPS points I captured with the Leica unit into Pix4D software and it was just miles off from the testing site.



This is the workflow I followed during my test:

1) Plan flight with DroneDeploy

2) Arrived to field. Turned on base station (Leica GS16) and rover (Leica GS18T). Made sure to get an accurate reading down to centimeter-accuracy. The base had a few options for the setup which is: set "over a known point," or "over any point." I chose over any point. Coordinate system was set to my local stateplane coordinate system NAD83 MA11. (I'm based in Guam)

3) I laid out 5 GCP pads evenly across the field and went to each one with my Leica rover to collect the center point.

4) After points were collected, GPS units were packed away and I proceeded to the drone flight plan via DroneDeploy.

5) Go back to office, start a new project in Pix4D, upload the photos, set the coordinate to the state plane, process step 1 and import the GCP coordinates via GCP/MTP manager.

6) This is where it goes all wrong. It immediately gives me a prompt saying one or more GCP points are far away from your site. When I click "okay" to just proceed anyways, the GCP points are miles away from the the testing site.



I'm pulling my hair not knowing what went wrong and been trying to figure this thing out for two weeks now. What I'm assuming I'm not doing correctly is the workflow with the GPS unit?

I've been reading a lot into this and I hear surveyors typically position their base station directly over a "known point" or a "survey monument" when they're capturing coordinates with their rover.



Some burning questions I'm itching to get answers for:

1) Am I supposed to place my base station directly over a "known point" or "survey monument" for every job if I want to get accurate measurements?

2) Or am I doing something else wrong like the coordinate system settings?

3) What is typically the workflow for drone mapping with an RTK GPS system? (RTK system meaning base + rover. Unfortunately accessing the NTRIP network is not available in Guam apparently)




I would really appreciate any insight as to what I can do to correct this issue.
 

R Martin

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2) Arrived to field. Turned on base station (Leica GS16) and rover (Leica GS18T). Made sure to get an accurate reading down to centimeter-accuracy. The base had a few options for the setup which is: set "over a known point," or "over any point." I chose over any point. Coordinate system was set to my local stateplane coordinate system NAD83 MA11. (I'm based in Guam)
My unit (not a Leica) requires that I enter the location it occupies. If you don't accurately locate the base station what is the point in using it? Just go with an RTK stream in the latter case.
 

chasco

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Make sure your columns for your GCP coordinate file are mapped correctly and Northing and Easting aren't reversed.

Make sure the EPSG zone is correct if you are close to a limit. We sometimes have trouble when we get to an area where Texas Central and South Central overlap.

Setting up on any point is averaging and will only be within 5-10 meters, but that wouldn't cause a separation like that. Do you have any CAD data or points to tie to? I would consider a localization.
 
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SWA Pilot

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Drone u has a good class on their web page (thedroneu.com) Comprehensive mapping...starts at video 5. Common problems...mixing Northern and Easting (x,y,z), check all images (look for sensor error image...overheated sensor), reoptomize, might need to remove altitude data for drone photos (z axis)...to name a few.
 
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chasco

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mixing Northern and Easting (x,y,z)
No dig, but it's funny you wrote it this way... NEH is YXZ. I see it all the time where it is easy to get mixed up because terminology always states XYZ when survey grid coordinates are almost always YXZ. Latitude, Longitude and Ellipsoid Height is LLh and XYZ. Like it wasn't already confusing enough. 🙂
 
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nikorasa

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Hi!

A lot of good hints there already. Make also sure you do not change the image coordinate system when uploading the photos from Phantom to Pix4D. You should change only the output coordinate system.

The (x, y) mixing is probably the most frequent problem as said earlier. The problem with z coordinate usually comes only after importing GPS-data and when trying to mark those GCP's in rayCloud editor. If photo's are not showing when clicking GCP in RayCloud you should use the old fashioned Basic GCP/MTP editor for first 3 points and then reoptimize. After that you can mark more GCP's with rayCloud.
 

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