Basic question on how mapping works

[arruntus]

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.

 

[Fin]

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.

Arruntus the Gps will be 15-30mm accuracy/ in a quarry the horizon is reduced so the pdop can be poor. Then the accuracy of the picked gcp and then the GSD all combine. The tolerance is tighter by the GCP but beyond gets worse.

This video is done in one scenario with ideal conditions.. in a quarry flight is 80m AGL minimum... Ground is not consistent..

 

[Panomapic]

I feel like this all is not to say that drone mapping and photogrammetry using those products are not useful. There is just a need to know your accuracy and to be truthful about it.

 

[arruntus]

I agree with everyone, I have put myself in the case with more difficulty to try to justify the use of ground tracking and where it may be most useful.

In the case of the quarry, the base can be set to "level 0" and in direct view with the Rober. It will eliminate the vision problems of the GPS of the Rober. The correction is done in real time and therefore not only the georeferencing will be done correctly, but also the flight itself.

This video is done in one scenario with ideal conditions.. in a quarry flight is 80m AGL minimum... Ground is not consistent..

I totally agree, and he already comments on it in the video, it's a planimetric example. As soon as different elevations of the field come into play, the matter changes. It helps us to see how far we can go with this system. I believe that in these cases, even if you use a RTK system, it is necessary to use a lot of GPC's measured with a total station.

Combining the best of both systems I think you can get very good results. Theoretically, I have to rely more on the opinions of those of you who have done that kind of testing. I have been studying the subject for a long time because I will probably have to do it in several quarries and I want to be prepared by working with a surveyor who will confirm the data obtained.

If he finally get the contract, and we do the inspections I'll tell you how it goes.