I map and use a Geo 7X with a centimeter mapping package installed as well as AeroPoints for control. All of our contracts require a minimum of six surveyed benchmarks to be set in accordance with USGS specs (outsourced to a local surveyor). We are mainly involved in subsurface utility work but also do before and after as well as job progress (if we must).Those doing ‘mapping’ for clients, are you using gcp’s? If not, what type of deliverables are construction clients commonly asking for?
Your usage of GCP and reasoning is how I've understood it. That rational increases as size of the image increases. It also helps increase the alignment of the images when the GCPs are identified in a several images.GCPs are points (targets) on the ground that are surveyed and visible in the aerial photos. I use white 5-gal bucket lids as GCP targets. I‘ve drilled a hole in the center of the lids so I can pin them to the ground with a large nail and carry them in a stack on a “stringer“ I made. The heads of the nails or holes in the lids are often visible in the photos, which helps us enter coordinates of the GCPs in the photo processing software. We survey the coordinates of the GCPs using RTK GPS or other survey instruments (robotic total station, etc.). You can also use painted GCPs, prominent features that appear in the photos, etc., but you need to survey or know the location of all GCPs. There are also commercially made GCP targets that have RTK GPS receivers built into them but they are expensive and I wonder about their ability to “see” the sky/GPS satellites when sitting on the ground.
GCPs are necessary for best accuracy of an aerial survey because they allow the processing software to correct distortions that may be in the photos/photo mosaic from various sources. An RTK GPS receiver on the aircraft also improves accuracy of the survey by providing better locations of the photographs, but you need GCPs to correct for other errors such as distortions caused by the camera lens, and camera movement and tilt that are too small for the sensors on the aircraft to resolve and record. I use GCPs and no RTK on the aircraft all the time.
Hope all is good with company & families... noticed the passing of Chaz. He sounded like one heck of a guy!GCP's of some sort in every map. Yes, there are several methods and centimeter accuracy is not always required nor is GNSS equipment. No RTK as it is not acceptable for certified mapping without logging, but PPK on all phase grade verifications and asbuilts.