Aerial Targets

I just completed a similar project and we used "identifiable objects" when ever possible. You may note that some municipalities required a "Permit to Work in the Right-of-Way" if we wanted to paint a target in the street. Pain in the kiester plus they wanted a fee per each target painted as each was located in a different road right-of-way.

Probably both.
jud

We have done several photo projects using both painted on targets (usually on the road shoulders) and nail down targets. Generally you will need a mix if you have any rural areas in the flight line. And of course, it depends on the density required by the flight company and spacing.

The painted ones are zero maintainence but the nail down ones are a pain at times with the wind and other factors. The weather (clouds) dictate the flight schedule so often it requires several trips to check on the targets.

We have used 'some' photo identifiable points but these tend, at least to me, to be somewhat less reliable as a distinct X on the photo.

Very important is the sky view of each point so that you can occupy and get a solid position. For aerials then I've always done static sessions and a network adjustment. I know that many use RTK, but I think the extra time is well worth it for all the subsequent uses that the aerial will often provide. Planimetrics and more.

When ordering flights for a private contract or for flights as a city then I've always added in X amount of targets (usually 10%) that I did NOT supply to the flight company as my way of internal quality control checks on the final product.

I've seen some cities use fire hydrants or SSMH's lids that they painted white to use as photo targets. These projects have ALL been very problematic with the finished products. I'd stay away from these sorts of targets.

dp

The flight altitude can be a factor when deciding targets. For low (2500' agl +/-) altitudes we use to use old found car tires, painted white and staked down securely over control points. They show up great on the photo.

We also had some 2'x8' plywood targets for higher camera altitudes, they are a pain in the butt if you can't get the truck to the target site.

Existing photo points are always good as long as they are described eloquently and in short or no grass or shadows...

I have done 100% post ID, 100% targets and combinations. It depends a lot on what is "potentially" available for post ID, scheduling, etc. For the most part, it takes about as many hours to do the job either way (of course you can bump the flying schedule to immediately with post ID), probably less effort in some cases to just go ahead and set the targets, trying to find something suitable in very rural areas is sometimes a challenge. Quite often there may be stuff out there, poles, fence corners, etc., BUT those require more effort due to being some sort of offset situation. Somewhat driving the decision may also be the accuracy required, especially as it pertains to non ideal post ID points (especially for the vertical) if you go that route. Picking post ID points can sometimes be a real art to know what will work and what won't work. Another consideration is whether there will be AGPS/IMU on the photo platform, that adds more flexibility in moving targets around vs. a fully ground controlled project, especially as it relates to post ID targets. Sometimes there will be suitable post ID objects, BUT you can't obtain access, in those cases obviously setting your own nearby on ground that is public or for which you have permission to enter is a factor.

If the area were ALL urban with lots of pavement markings, curbs, sidewalks, etc., then I would probably go the post ID route, otherwise you are going to have to make some decisions on a case by case basis. In addition, post ID points that are NOT ideal, will degrade the final product accuracy somewhat. One final consideration is the safety factor, sometimes a CL road stripe would technically work just fine, BUT isn't as safe maybe as something 50 feet away out of the traffic so that might dictate a pre mark too.

My business is almost exclusively as a ground control surveyor for aerial projects both imagery and LiDAR, while this type of work sounds pretty straight forward, like anything else you become good at it with lots of experience in setting points and picking post ID points. I have had otherwise experienced surveyors mess this up bad when working for me and sometimes with production at about 1/4 of what I could do, just because they debated with themselves all day long if this or that would work. A key to this type of work is lots of two way communications with the mapping company!!!

SHG

When ordering flights for a private contract or for flights as a city then I've always added in X amount of targets (usually 10%) that I did NOT supply to the flight company as my way of internal quality control checks on the final product.
Derel,
we usually do this too - we call them "blind panels". usually a corner of a structure, sidewalk, even a cross walk stripe corner if clearly defined. whatever we can locate and have tight X,Y+Z as a check.
one more thing we usually supply to the aerial co if we're surveying a roadway, is our topo shots along the E/P - seems to really tighten up their DTM and helps with better contours for design.