Mapping - elevation and dimension accuracy

Plingboot · Dec 19, 2016

I've been asked to do a mapping survey of a construction site for a friend - which makes it an ideal project to get into this kind of work.

To manage expectation, how accurate is the elevation and dimension data which can be taken from the finished maps? I'm considering DroneDeploy for this first job.

The object of the exercise from his point of view is to replace a traditional survey done by a man with a tape measure with something more detailed, accurate and useful.

G6 VisionHawk · Dec 19, 2016

I'm just getting ready to start flying doing ag work. I am also interested flying construction and will be using precisionhawks algorithm market place.

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southerndoug · Dec 19, 2016

Plingboot said:
I've been asked to do a mapping survey of a construction site for a friend - which makes it an ideal project to get into this kind of work.

To manage expectation, how accurate is the elevation and dimension data which can be taken from the finished maps? I'm considering DroneDeploy for this first job.

The object of the exercise from his point of view is to replace a traditional survey done by a man with a tape measure with something more detailed, accurate and useful.

There's some good starting info here for expectation management (if you haven't already seen it):

DroneDeploy

I've been using Map Pilot and Maps Made Easy, which is far cheaper than DD.

Plingboot · Dec 20, 2016

Thanks for the DD accuracy link, i'd not seen that.
Will also have a look at MME and MP.

Mgraywv · Dec 20, 2016

I use UGCS for mission planning and PIX4d to procees the imagery. We do a lot of what you are looking to do. We use survey mapping standards which says 90% of the data has to be at 1/2 contour interval. So, we do 2 foot contours so our data should be less than a foot. I set Ground control Points (targets) than I shoot random shots throughout the site for data validation.Usually my data is around a tenth of a foot.

Plingboot · Dec 21, 2016

Could you explain what half contour intervals means?

Mgraywv · Dec 21, 2016

yes. If you are flying to create a topographic map and you produce a map that shows contours on 2 ft intervals you need to validate that where the drone says the elevation (contour line) is correct. You can do this by comparing the UAV contours to some type of existing contours, surveyed topo or from actual surveyed or GPS shots. The accuracy of your contours need to be within 1/2 a contour interval. So if you were producing 2 ft contours the accuracy needs to be at least 1 foot on 90% of your data. I have attached an image of an example of the data validation that I use this may make more sense.

Plingboot · Dec 21, 2016

Thanks, very helpful indeed much appreciated.

I'm aware that there are many factors involved, but assuming a 'good' set of images and some accurate reference pints, In comparison to having a surveyor survey a site using whatever you'd class as standard ground based techniques, how well does an aerial survey compare in terms of accuracy, detail and usefulness to the client?

i.e. Is the aerial survey adding value?

Mgraywv · Dec 21, 2016

The sites I have flown have been very accurate. However, I use a good bit of ground control points. Most of my sites are around 30 acres and I usually put down around 10 -15 Ground Control Points (Targets)

The_Learning_Curve · Dec 21, 2016

I've been caught up on a lot of other applications and surveying is something I'd like to start tackling. After reading this, it seems there's much more to do than just flying the missions to get the accurate results. Are there pretty detailed instructions from the software developers that enables newbies to learn what they need to know or are we going to be relying on outside resources to learn the techniques to produce accurate results?

Has anyone used precision hawks apps? They're the first ones that comes to mind when I'm considering software for surveying.

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Plingboot · Dec 21, 2016

@Mgraywv, do you have any recommendations for gps devices for ground based reference points. Googling 'cm accurate gps' doesn't really yield much in the way of useful info..

Boycie702 · Dec 24, 2016

I understand that to be classed as "survey grade" you need to be able to achieve an accuracy of less than 3cm with your kit. That won't happen unless, as other have suggested, you are using ground control points (GCPs) and, in turn, surveying the location of those points with a "survey grade gps" (rather than a "cm accurate gps" Plingboot). A survey grade GPS will be able to triangulate down to about 2cm and the location of your GCPs will enable your software to twist your orthomosaic and achieve an accurate survey.

As far as I know, Dronedeploy doesn't have the ability to input GCPs but it no doubt will develop as more people use drones in survey. A survey grade GPS to generate your GCP will cost upwards of $10k. That's why survey costs a lot and we aren't all about to sweep up the world market in surveying with a $600 drone off Amazon.

If you aren't using a survey grade GPS and the survey grade software like PIX4Dbim then all you are producing is a nice picture of a build site with a particular (high/low) resolution. That may be useful to some developers...but it isn't a survey.

Eric Braun · Dec 24, 2016

Boycie702 said:
I understand that to be classed as "survey grade" you need to be able to achieve an accuracy of less than 3cm with your kit. That won't happen unless, as other have suggested, you are using ground control points (GCPs) and, in turn, surveying the location of those points with a "survey grade gps" (rather than a "cm accurate gps" Plingboot). A survey grade GPS will be able to triangulate down to about 2cm and the location of your GCPs will enable your software to twist your orthomosaic and achieve an accurate survey.

As far as I know, Dronedeploy doesn't have the ability to input GCPs but it no doubt will develop as more people use drones in survey. A survey grade GPS to generate your GCP will cost upwards of $10k. That's why survey costs a lot and we aren't all about to sweep up the world market in surveying with a $600 drone off Amazon.

If you aren't using a survey grade GPS and the survey grade software like PIX4Dbim then all you are producing is a nice picture of a build site with a particular (high/low) resolution. That may be useful to some developers...but it isn't a survey.

And if you're trying to sell your work product without a surveyor's license it's a moot point anyway. You've gotta team with a surveyor or be one yourself to have your accuracy really matter.

IrishSights · Dec 24, 2016

Eric Braun said:
And if you're trying to sell your work product without a surveyor's license it's a moot point anyway. You've gotta team with a surveyor or be one yourself to have your accuracy really matter.

In the US. Not true everywhere.

PfCO Holder
BNUC-S Qualified

airbud · Dec 27, 2016

Eric Braun said:
And if you're trying to sell your work product without a surveyor's license it's a moot point anyway. You've gotta team with a surveyor or be one yourself to have your accuracy really matter.

Curious if you know what the requirements are when teaming with a surveyor. Just he just need to sign off?

Eric Braun · Dec 27, 2016

airbud said:
Curious if you know what the requirements are when teaming with a surveyor. Just he just need to sign off?

I think so. So our job would be convincing the surveyor to put his license on the line and that there's a compelling reason to do so. Checkshots, ground truthing would probably be necessary.

airbud · Dec 27, 2016

Eric Braun said:
I think so. So our job would be convincing the surveyor to put his license on the line and that there's a compelling reason to do so. Checkshots, ground truthing would probably be necessary.

Copy, thanks.