arruntus
Premium Pilot
- Joined
- Aug 19, 2017
- Messages
- 1,851
- Reaction score
- 730
Arruntus these are all tests done by the software vendors.
I am a land surveyor with 20 years experience in mapping. Using GPS and Total Stations.
The amount of work required to get a survey to sub 10mm you would not believe!!!
I have carried out many tests myself and I did encounter a model which had 3m error in height on the top of some areas.
The ground had very significant level differences and only 6 GCP placed. The only way to ensure a good model is to place many more GCP.
I now place approximately 20 on this site. And they have to be placed in certain places to get an accurate model. On a flat smooth site you will get better results.
You will never get 10mm with photogrammetry or even Lidar.. GPS will only get this after Static OBS and post processing for at least 30minutes on a tripod..
When you have completed 25-30 surveys on the same site using GPS and Total Station data to compare with your photogrammetry then you will know.
I survey the same 3 sites every 30 days - and have been doing so for nearly 2 years. The data is never any closer than 50mm in accuracy on the areas which do not change - no matter what is done. Even using the same GCP points you will get a different result.
I don't mean to contradict you because the first thing I respect is experience. Accuracy of the 2.5cm XY range is being achieved with a drone and RTK. In Z, the rule of 1 to 3 is usually fulfilled. In addition, the use of GPC is largely eliminated, and it is advisable to use them only for control purposes.
It is when there is a marked slope that the problems appear. In fact, in another forum I was asking it to try to get a standardized answer. In that case the discussion was about landfill projects where there were a large number of stockpiles. In the end, in order to achieve the highest possible accuracy in Z, it seems that it was necessary to put a GPC at each top of the stockpile.
The RTK system is very much like the total station process when you have a good network connection. Depending on the equipment, the quality is fundamental, in principle then the correction in real time should be quite precise. If we add good GPC points to this, I believe, in my modest opinion, that good data can be stored around 3cm accuracy. This is considered valid in most civil works. Then this data as applied in reality, after the enormous work it takes to get good data, is often a laughing matter. What's the difference a foot over there? Until the surveyor comes along and starts cursing


Watch the first video because it compares total station, drone and GPS. It's a shame we don't know what equipment the drone had.