No ground control needed?

two things:

1.been looking at buying a drone and find this line of marketing kind of quaint myself. and it may well be the case, but you best believe i'm setting GC points and referencing against them if i fly something. why wouldn't you? you're cutting the "ground" time of any given job down by AT LEAST half, not sure why you wouldn't spend a small fraction of total work time doing basic- even if theoretically superfluous- redundancy checks.

2. almost forgot i start pilot's license classes on monday. thanks for the reminder!

[USER=640]@John Hamilton[/USER] I suppose I will believe it when they can derive 3D on a bunch of hard objects with enough accuracy to meet the desired spec of the final mapping. I have never seen that for better than say 1" = 500' scale mapping.

Until that technology arrives (and is proven) we need to stay with known methods.

stereo controlled boundary anyone?

Off topic a bit, but perhaps interesting...
Back in the early 70s I was a grunt on a crew staking a bunch of 20 or 30 acre lots on the Northern Ca. Coast. Heavily wooded, but with scattered clearings. Somehow there was control, and it was mapped with conventional (at the time) stereo imaging. Contours and tree lines and roads... but the added twist of uncontrolled photo panels, set in pairs in the clearings. The stereo plotter operator (a mentor of mine) created coordinates on them...
Our task, as field grunts, was to set on one, back-site another, then set new interior boundary points (tagged iron pipes). It went well, most back-site distances fit to within just a few tenths.
For the time and the place, that was just fine.
I don't remember any complaints in the office of budget problems, nor did I hear any talk of huge savings.

I do know it was cold, wet, and windy. traversing thru that subdivision to create conventional control would have taken months.

flyin solo, post: 391136, member: 8089 wrote: almost forgot i start pilot's license classes on monday

Have fun.

I may be taking the post off on a tangent, but here goes.

Twenty years ago I had one of our photogrammetrist call my field office because she couldn't get one BM (control point) to focus. After much inspection I found I had transposed a hand entered elevation and the difference was 0.18'. Quite remarkable I thought. The industry has only advanced since then.

But for a rhetorical discussion about "No ground control needed", I cringe at the thought even though high levels of confidence can be had. Color me "old school".

They did say a few times that of course the professional mapping companies always set some control. I have processed a lot of airborne GPS (none recently), and it sometimes has serious problems. At the least I would think a client would want plenty of check points.

I fly a Trimble UX5-HP and you absolutely need ground control unless you don't care if you're coordinates are real-world accurate. To their credit, in all the training and seminars I've had on it Trimble has never claimed otherwise. In fact, in the UX5-HP webinar the first thing they said was you still need ground control.

I don't know how much having the inertial onboard improves the accuracy, but my experience is that the PPK trajectories are typically +/- 1 - 3 decimeters.

Lee D, post: 391180, member: 7971 wrote: I fly a Trimble UX5-HP and you absolutely need ground control unless you don't care if you're coordinates are real-world accurate. To their credit, in all the training and seminars I've had on it Trimble has never claimed otherwise. In fact, in the UX5-HP webinar the first thing they said was you still need ground control.

I don't know how much having the inertial onboard improves the accuracy, but my experience is that the PPK trajectories are typically +/- 1 - 3 decimeters.

When a drone is purchased and it's going to do regular photogrammetry, is there a big advantage if the drone has RTK in it instead of autonomous GPS?

paden cash, post: 391172, member: 20 wrote: I may be taking the post off on a tangent, but here goes.

Twenty years ago I had one of our photogrammetrist call my field office because she couldn't get one BM (control point) to focus. After much inspection I found I had transposed a hand entered elevation and the difference was 0.18'. Quite remarkable I thought. The industry has only advanced since then.

But for a rhetorical discussion about "No ground control needed", I cringe at the thought even though high levels of confidence can be had. Color me "old school".

Everyone probably already knows this, but if you accidentally flip the last two digits of a number, the difference is always a multiple of 9. 64 vs 46, 64-46=18
52-25=27 18 or 27 is a multiple of 9

MightyMoe, post: 391183, member: 700 wrote: When a drone is purchased and it's going to do regular photogrammetry, is there a big advantage if the drone has RTK in it instead of autonomous GPS?

I've seen one or two other posts on here about drones with RTK onboard but I haven't researched them. The GNSS receiver on the UX5-HP is totally passive; it's not used for navigation and is not connected to the autopilot, which has its own meter level GPS. It collects static data at 20Hz so that you can post process your flight lines, and receives event markers whenever the camera is triggered. I would say, based on my relatively limited knowledge and experience, that it reduces the need for ground control because the camera positions are pretty accurate after the flight has been processed. I've done some limited testing - limited because anything involving UAS data processing is time consuming - and the positions obtained without using GCP are surprisingly accurate. But you still need at least a few GCPs to tie you in to accurate coordinates and to ground truth the data.

The added bonus of having the onboard GNSS is that after you process the trajectory you can look at a 3D view and get a very good visualization of the flight path. This comes in handy, especially when, like me, you're trying to learn all that you can about how the aircraft behaves.

"Drone" is a very generic term... I could see how RTK might be beneficial on a rotary craft because you could accurately track its position in real time. On a fixed wing aircraft like the UX5, the flight plan is pre-programmed and there is little to no interaction with the plane after it's launched unless something goes wrong.

Tom Adams, post: 391189, member: 7285 wrote: Everyone probably already knows this, but if you accidentally flip the last two digits of a number, the difference is always a multiple of 9. 64 vs 46, 64-46=18
52-25=27 18 or 27 is a multiple of 9

Didn't know that!! That is cool!

John Hamilton, post: 391132, member: 640 wrote: I went to an interesting conference this week in Toronto. It was the Applanix Airborne User Group meeting and conference. A lot of the talk was about "you don't need ground control anymore", aka "direct georeferencing". The combination of on-board IMU and GNSS means surveyed ground control is now superfluous (according to them). Of course I don't agree. I have definitely seen a large reduction in the amount of ground control for photogrammetry and Lidar, but fortunately my clients still want at least some in order to be able to say they met xxx accuracy and to make sure they are accurately tied in to the datums. And specs often require a certain amount.

I would have to add my vote in for wanting to see actual data and studies t prove this before blanket agreement. In California, mapping by photogrammetric methods is defined within the practice of land surveying and in some cases is allowed under the civil engineer license. I've always looked at the choice of using this method over traditional field topography methods in terms of cost, time, and client needs. But either way, the photogrammetrist is really just another form of "field crew" and "drafter" for me in lieu of the traditional staff. And I, as the licensee who is required to put my seal and signature on the final topographic map, am still the authorized individual who can provide mapping to the public. Photogrammetric firms that would promote this methodology would need to abide by the California licensing laws by having an appropriately licensed individual in responsible charge of that work, ground control or otherwise.

flyin solo, post: 391136, member: 8089 wrote: two things:

1.been looking at buying a drone and find this line of marketing kind of quaint myself. and it may well be the case, but you best believe i'm setting GC points and referencing against them if i fly something. why wouldn't you? you're cutting the "ground" time of any given job down by AT LEAST half, not sure why you wouldn't spend a small fraction of total work time doing basic- even if theoretically superfluous- redundancy checks.

2. almost forgot i start pilot's license classes on monday. thanks for the reminder!

I recommend Wolfgang Langewiesche's classic book, Stick and Rudder.

Also new students should do a lot of slow flight, the effect of control movements are more obvious.

Dave Karoly, post: 391246, member: 94 wrote: I recommend Wolfgang Langewiesche's classic book, Stick and Rudder.

Also new students should do a lot of slow flight, the effect of control movements are more obvious.

thanks! signed up for this on a lark, not sure where it'll go. honestly don't know when i'll have time to do the flying, but the class is cheap and being offered as an extension class at THE university of texas (their emphasis, not mine), which is just a leisurely walk from the house. Mainly a built-in excuse to get away from the estrogen factory for a couple hours a week for the next little while.

I enjoy just going out and flying around for an hour or so on weekends, it is my way to get away from everything. I do also fly some for business on short trips. For example the trip to Toronto was about 1h45m flying, 6 hours driving, plus however long it would have taken at the bridge, which does get backed up. So I save a total of at least 8h30m (assuming no delay crossing). I wish I would have taken flying lessons in college (at Purdue, they offered it cheap at that time in the mid 80's), but instead I waited until I was in my early 40's to start.

Ric Moore, post: 391209, member: 731 wrote:

I see this as being a big issue in the future, the question of whether the mapping is being done under supervision of a qualified person, however that might be defined.

john, that's where i am on the timeline. it's been in the back of my head since i was a kid, but like most things this came down to an impulsive decision: signed up within hours of getting back from yet another united airlines gauntlet.

flyin solo, post: 391320, member: 8089 wrote: john, that's where i am on the timeline. it's been in the back of my head since i was a kid, but like most things this came down to an impulsive decision: signed up within hours of getting back from yet another united airlines gauntlet.

I currently have a share in a flying club, 29 members, 3 planes. Sounds like a lot of members for a few planes, but in reality about half or less fly regularly. We have very reasonable rates, much cheaper than renting from a third party like a flying school. Also cheaper than owning a plane under almost any circumstance. the only benefit to owning a plane myself would be that it would always be available on demand. But, having three planes in the club means at least one is almost always available. We have a Skylane (C182), a Cardinal (C177), and a Tiger (Grumman), I only fly the cessnas typically.