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What do you all use for "Checkpoints" during mapping missions?

jonscardenas

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Hello, I work in Forensics for law enforcement and I am currently establishing policies for our drone missions. Predominantly, we will be using our drones for mapping of large scenes to supplement our laser scan data. With our laser scans, we validate them with an object of fixed and known length; its essentially a pole sitting on a tripod with a target on each end. The known distance between the two targets is about 3.28 ft and we can verify on scene that our laser scanner is working and properly calibrated if the distance measured between the two targets is within our margin of error. Unfortunately, our current equipment is too small for our EVO II to pick up from 100+ feet, so we are looking for something larger.

What are you all using for validation for mapping use? Obviously, we could just measure the distance (by hand) between fixed objects within our scene (paint markings and other physical objects in our scene) but for our purposes, we would like something that would be used in all case work. Not to mention it would be easier and more likely to be measured the same, every time, regardless of the pilot.

We are looking for something portable, as small as possible but still useable at 200 or so feet. Is there anything on the market? I honestly, might just build one, using some threaded pipe and some 1/4" steel with high-vis paint for make shift targets but I would like to see if theres anything out there at a reasonable price before diving in. Thanks
 

jaja6009

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Hello,

I fly drones for Public Safety/Fire Side. What you are describing is what Pix4D (Photogrammetry/Mapping Software) calls a scale constraint. I use a 12' 2x4" with the ends painted blue. The space between the blue is 10'. Not the most portable item, but it does fit in my Durango.

Per Pix4D when using scale constraints longer is better and do not be afraid to also go vertical with them too.

Are you also going to be using GCP (Ground Control Points) to better your absolute (placement in the real world) accuracy? If so you may not need scale constraints.

Some Pix4D info on the subject:
 
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jonscardenas

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Greetings! We will be using GCP's which will be measured independently with our Total Station surveyor and then input into Pix4d. As far as I know, we will not be using scale constraints within pix4d but I will have to clear that up. The "check points" as far as I know, will strictly be used to validate our drones accuracy. Not sure if these will have to be manually entered into the Pix4D as well, or if they can be measured out separately (if need be) within the orthomosaic or point cloud.
 

jaja6009

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Pix4D Workflow

Arrive on scene plan area to be mapped.
Lay out ground targets in appropriate manner depending on size and shape of AOI. Use enough so you have both GCPs and Check Points. Check Points are entered when you do GCPs, but they are not used by the software during processing, they are used afterwards to see how well your map is in terms of absolute accuracy (its placement in the real world).
Use Total Station to get GCPs and Check Points location.
Run Pix4D Step 1
Add GCPs and Check Points
Reoptimize and then run Steps 2 and 3

You can use scale constraints also that can be processed or you can have the scale constraint item to check relative accuracy on the completed project. You can measure in the Point Cloud to see how close it is to its real dimensions.

In my opinion, since you are using GCPs you do not need to add the scale constraints, and this will help take a step out of your workflow.

Also make sure you know how to place GCPs based on the shape and size of the AOI.

Hopefully some experts will chime in. I have made maps using GCPs but there are others out there that do this on a daily basis and do achieve centimeter level absolute accuracy and their experience is often priceless.
 

jonscardenas

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Gotcha. As far as I know, our Pix4D instructor is against using scale constraints after running into a lot of issues with it so we are solely relying on GCP's at this point.
 

jonscardenas

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Perhaps, might be a little small to be picked up at altitude. At least the ones that I am seeing on google seem small.
 

Antoine.scuba

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Hello, I work in Forensics for law enforcement and I am currently establishing policies for our drone missions. Predominantly, we will be using our drones for mapping of large scenes to supplement our laser scan data. With our laser scans, we validate them with an object of fixed and known length; its essentially a pole sitting on a tripod with a target on each end. The known distance between the two targets is about 3.28 ft and we can verify on scene that our laser scanner is working and properly calibrated if the distance measured between the two targets is within our margin of error. Unfortunately, our current equipment is too small for our EVO II to pick up from 100+ feet, so we are looking for something larger.

What are you all using for validation for mapping use? Obviously, we could just measure the distance (by hand) between fixed objects within our scene (paint markings and other physical objects in our scene) but for our purposes, we would like something that would be used in all case work. Not to mention it would be easier and more likely to be measured the same, every time, regardless of the pilot.

We are looking for something portable, as small as possible but still useable at 200 or so feet. Is there anything on the market? I honestly, might just build one, using some threaded pipe and some 1/4" steel with high-vis paint for make shift targets but I would like to see if theres anything out there at a reasonable price before diving in. Thanks
I have flown lots of missions for mapping.
What we use for GCP's are homemade white Styrofoam targets, 2'x2' with high visibility paint(Orange) painted so as to highlight the center. those are easily visible up to 100m(400') and space them at 100m apart, quite often closer to 200m and with px4D it will get you 2cm accuracy. Run the GPS at the same time so you use the same gps information, better results.

If you have an RTK drone (Evo II is coming up with one), all you need is setting up the gps that comes with the kit and only need to create one GCP .Good luck
 

jonscardenas

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So it's my understanding, from our Pix4D instructional class, is that GCP's and check points are independent of one another. For GCP's we are using 2x2 circular targets (more or less look similar to a landing pad). I don't quite see what the point of using both is honestly since our GCP's are measured with a total station and the distances basically can be verified/validated as well.
 

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