People in charge

..................70 targets?????

?ÿ

How monstrous is that site?! That seems extremely extremely excessive

The City can't convey property owned by others by Ordinance.

Posted by: Dave Karoly

The City can't convey property owned by others by Ordinance.

At least the city quit writing deeds for vacated property, now I think I have the county stopped. Who knows what will happen when the next batch gets elected.

Posted by: SuperiorRyan

..................70 targets?????

?ÿ

How monstrous is that site?! That seems extremely extremely excessive

He likes his control, the next area has about 100 that we will do for him. I don't do it, never had a good reason to buy one, but these people seem to get good answers and do a good job, I think the first site is about 60 acres.

Speaking pretty generally, thats way too many.?ÿ Granted I dont know how large the site is, or if its multiple sites etc, but I typically fly 150 acres with 6 GCP's and typically get a verified accuracy of 0.1' @ 400' (would be tighter if I flew lower).?ÿ Introducing a lot of extra GCP's has only brought the accuracy down in my experience.

?ÿ

(I've been using Pix4D and Sensefly drones for 6 years now)

Posted by: Dave Karoly

The City can't convey property owned by others by Ordinance.

How do you know the city doesn't own it? Who has the burden of proof?

I'm working on a survey, where the deed says, "except the south 20' for road", so does the neighbors; creating 110' of "road", 20' wide. This is access to a small parcel, that was never developed and the "road" never built. The survey is to consolidate 7 parcels and develop a commercial site (restaurant). the client wants to own the road, at least the part that adjoins his property.

Does the city own this "road"? If not, who does?

TIA

Dougie

Posted by: SuperiorRyan

Speaking pretty generally, thats way too many.?ÿ Granted I dont know how large the site is, or if its multiple sites etc, but I typically fly 150 acres with 6 GCP's and typically get a verified accuracy of 0.1' @ 400' (would be tighter if I flew lower).?ÿ Introducing a lot of extra GCP's has only brought the accuracy down in my experience.

?ÿ

(I've been using Pix4D and Sensefly drones for 6 years now)

I'm not an expert in these drone flights, I do know these guys set a lot of control, some of their clients want a lot of checks on the photo's, I think they have been burned by other flights.

We are?ÿthe grunts for these projects. And more than happy to do them, great guys to work with. ??ÿ

Posted by: RADAR

Posted by: Dave Karoly

The City can't convey property owned by others by Ordinance.

How do you know the city doesn't own it? Who has the burden of proof?

I'm working on a survey, where the deed says, "except the south 20' for road", so does the neighbors; creating 110' of "road", 20' wide. This is access to a small parcel, that was never developed and the "road" never built. The survey is to consolidate 7 parcels and develop a commercial site (restaurant). the client wants to own the road, at least the part that adjoins his property.

Does the city own this "road"? If not, who does?

TIA

Dougie

The city has a fee simple determinable ownership in a street created by statutory dedication. The abutters hold a possibility of reverter and the dedicator retains the minerals under the street.

If owned in fee the city can sell a street, but for statutory dedicated streets all they can do is vacate, the ownership of the street is already held by the?ÿlandowners with reversionary rights.

For your street it may be a private driveway with no public ownership, a different animal. If it is a dedicated street the state laws and court rulings would control.

"Introducing a lot of extra GCP's has only brought the accuracy down in my experience."

I'm sorry, but how can additional control possibly degrade the accuracy?

The City is purporting to convey a fee underlying an abandoned street to an abutter.

For example, if the Street was dedicated out of one owner (so-called marginal street) then it reverts back to whence it came, the City's ordinance is ineffective to convey half the street to the other abutter that never had any interest in that half of the street.

"Introducing a lot of extra GCP's has only brought the accuracy down in my experience"

?ÿ

Say what?

In my experience with air trig, more panels=better accuracy.?ÿ

As long as the panel coords and elev are accurate.?ÿ?ÿ

how many; is to many?

In my disscussiod with colleagues who specialize in aerial photogrammetry.?ÿ They say the more panels the better.?ÿ However one did mention the point of deminishing return.?ÿ When too many points and?ÿ

observations of more than 4 or 5 hours might result in less accurate results.

Introducing a lot of extra GCP's has only brought the accuracy down in my experience.

As others have implied, I think the phrase "brought the accuracy down" means "showed that the error estimates of a less well-controlled survey are unrealistic."

Posted by: Jim Frame

Introducing a lot of extra GCP's has only brought the accuracy down in my experience.

As others have implied, I think the phrase "brought the accuracy down" means "showed that the error estimates of a less well-controlled survey are unrealistic."

I've spent nearly 25 years rectifying imagery with GCPs.?ÿ Most of that has been for geologic exploration using satellite imagery.?ÿ There are instances where artifacts in the imagery will create problems with the rectification and having too many GCPs can create "tears" in the image.?ÿ More often than not this occurs with poor geometric distribution of the GCPs.

The other thing I'd like to mention is that the "extra" GCPs do not have to be used as control points to create the topographic model.?ÿ They can be reserved to evaluate the accuracy of the bare earth model created by the software.?ÿ Just like redundancy in least squares is a good thing, having a sufficient number of elevation residuals to evaluate the accuracy of the model is a good thing.

I could see more targets making for higher residuals, but not lower accuracy. Unless the targets themselves weren't accurate.

I know nothing about UAV topo mapping but have considerable experience in traditional (pre-GPS) photogrammetric mapping and would like to conjecture why UAV mapping requires so many GCPs.?ÿ

It's basically that UAVs fly low (400'+-) and airplanes fly high (2,500'+-) so a UAV job generates hundreds of "photos" compared with a few dozen photos using traditional photogrammetry for a site of size "X".?ÿ ?ÿThe required number of GCPs is basically a function of?ÿ the number of photos that have to be stitched together so to speak, so a UAV job would require an order of magnitude or more GCPs.?ÿ Also, a photogrammetric camera is an exquisite optical instrument, a UAV camera, not so much, so more GCPs would be required on a UAV job to better control camera distortion.?ÿ

I was puzzled by an above poster's statement that "I typically fly 150 acres with 6 GCP's and typically get a verified accuracy of 0.1' " but indeed, a quick surf revealed many UAV mapping firms quote those specifications.?ÿ Is the key that the UAV is using Airborne GPS/inertial to determine the location and platform orientation, etc., of the camera??ÿ Similarly, airborne GPS/inertial lowers the number of GCPs required in traditional photogrammetry, but the equipment involved is apples to oranges;?ÿ can a UAV carry a GPS that compares with the survey grade receiver(s) and ground base station(s) an airplane utilizes??ÿ Or is it simply that the UAV is low and slow compared to an airplane and doesn't need as accurate location/orientation data?

I'm really puzzled by the original poster's statement of 70 GCPs for 60 acres, and a replier's statement of 6 GCPs for 150 acres.?ÿ Somebody's going out of business if both are true.