GPS for Ground Control Points

[nwairphotos]

Can anyone recommend a basic GPS instrument that would be good for making ground control points to be used with mapping software?

 

[doktorinjh]

That's all going to depend on your budget and how accurate you need to be for your final products. There are some affordable solutions for under $1000 right now, which is much cheaper than a $20k Trimble R10, so it would be helpful to have a budget target.

 

[Blakedownunder]

Could setup something like Swiftnavs Piksi or any of these small L1/L2 band GNSS recievers.... Pretty sure they do an L1 only receiver too. Really.... you need access to an RTK system to make it super easy. I have a JAVAD system, but I'm also a surveyor..

 

[SHROP]

Basic equipment will yield basic results. GNSS is the way to go. Contact your local Trimble (or equivalent) dealer and rent the equipment or subcontract the gcp's out. Handheld GPS units will either be not accurate or not precise, almost never will they be both let alone one or the other. Equally as important as the tool gathering the data is the person interpreting it so allowing a professional familiar with gathering high precision location data to add their 0.02 cents to the collection is never a bad thing. I see contractors who use GPS machine controls think they are gathering good data when in reality they are not, then they call asking why things are off.
Best of luck!

 

[Kristina Fowler]

Just entering the world of 3D. I fly a P4P. Please tell me the primary differences between these GCP devices like those mentioned above vs. "X marks the spot", or physically placing visual marks on the ground in the images and calibrated in post production (AutoDesk applications). Thanks in advance....

 

[doktorinjh]

Please tell me the primary differences

There's a lot more to UAV mapping then just taking pictures, so I'll try to give you a brief overview. If you want to get an accurate and precise topographic map, 3D point cloud, or orthophoto, you're going to need to know where exactly in the world your model is being established. You can do that by knowing exactly where your ground control points (GCPs) are, or exactly where your UAV is when it took the picture (along with the pitch, roll, and yaw of the craft). GCPs are aerial targets that are then referenced in the software to nail down where things are in the real world. The precise UAV location data is processed and can be reasonably good, but is always improved with GCPs, although not nearly as many are needed. Once you've built your 3D model from the photos, the other products can be generated. Without precise data from GCPs or a highly accurate location for the UAV, you're just generating pretty pictures to look at. Does that answer your question?

 

[Kristina Fowler]

Yes - that does make sense. I was referring to actual spots on the ground (example: a 12-inch white disc). Generally, I understand the process of letting the camera know precisely where it is in addition to referencing GCPs placed in various overlapping images to let the processing app have proper reference points.

 

[doktorinjh]

I was referring to actual spots on the ground

I guess I'm lost as to what you're asking. We are currently using painted 5-gallon bucket lids and they work well, or at least up until about 300' AGL (with the P4P). For elevation check shots we may spray paint an X on the ground, since we're primarily interested in checking the vertical data. You can use anything that you can easily find in the air photos, though, including cracks in the pavement, parking stripes, a tree stump (probably not the best, though), etc.