Scanning for Topographical survey mapping of complex vacant land

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LPaulCook
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Scanning for Topographical survey mapping of complex vacant land

Post by LPaulCook »

As a licensed land surveyor I am often called on to do a boundary and topographical survey of vacant land. The map I produce will be the basis of the building and grading plans to follow. It must be very accurate and detailed. Oak trees are protected, Drip lines of the oak trees set building locations so they must be accurate as well. Rock and Boulders are important land features to be considered as well.

Having good control and targets in this type of situation is a must. Cloud to cloud registration will not work well, if at all and you can not georeference the scans to the boundary and official vertical datum of NAVD88 accurately without targets.

Here is an example of such a job we did yesterday in half a day round trip, plus processing the same afternoon. If the targets are set property and the setting are set correctly in SCENE the entire set of scans can be processed and registered correctly without intervention. Such was the case here. This was finished before dinner the same day!

We use 200mm spheres around the site and checkered targets taped over control points which are spikes and washers we set in the pavement. The CPs will be GPS surveyed at later time to georeference them and the scans to the boundary data and NAVD88 vertical datum.

Here's a 2 minute video I made this morning which shows the scan position and the registered (green colored) spheres as you view the property.
https://vimeo.com/389309506

Here is the overview map.
PAINTED CAVE SM LOTS CPs.png
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by gsisman »

LPaulCook wrote: Tue Feb 04, 2020 8:21 pm As a licensed land surveyor I am often called on to do a boundary and topographical survey of vacant land. The map I produce will be the basis of the building and grading plans to follow. It must be very accurate and detailed. Oak trees are protected, Drip lines of the oak trees set building locations so they must be accurate as well. Rock and Boulders are important land features to be considered as well.

Having good control and targets in this type of situation is a must. Cloud to cloud registration will not work well, if at all and you can not georeference the scans to the boundary and official vertical datum of NAVD88 accurately without targets.

Here is an example of such a job we did yesterday in half a day round trip, plus processing the same afternoon. If the targets are set property and the setting are set correctly in SCENE the entire set of scans can be processed and registered correctly without intervention. Such was the case here. This was finished before dinner the same day!

We use 200mm spheres around the site and checkered targets taped over control points which are spikes and washers we set in the pavement. The CPs will be GPS surveyed at later time to georeference them and the scans to the boundary data and NAVD88 vertical datum.

Here's a 2 minute video I made this morning which shows the scan position and the registered (green colored) spheres as you view the property.
https://vimeo.com/389309506

Here is the overview map.
PAINTED CAVE SM LOTS CPs.png

Nice Paul! Targets are the key. The question I have is about the control. Is you scanner a dual axis compensated? If not I feel you should have at least one more target in the rear to create a tilt check on the plain of the CP's, or maybe even a 4th to have a check on that plane
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by LPaulCook »

Steve,

Good point if one doesn't have dual axes compensators.

Fortunately the FARO S350 does. I've checked their accuracy many times.

Also, I close the loop back to spheres I leave from my first scans. In this case I started at the NW and worked my way around counter clockwise back to the POB.
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by stutosney »

Hi Paul,

Looks good and interesting you use scanning for topo. Do you not get issues with ground levels where the grass is a bit longer etc? I have just scanned a large topo site myself, all hard standing though. What software do you use to extract the features such as walls, buildings and ground features?

Thnaks,
Stu
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by scanster1 »

Hey Paul,

How are you extracting the data from the point cloud when needed? Or does the client drop utilize the point cloud? Scene needs an add-on to do this and I am not convinced it works that great, at least until I try it for myself.

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Re: Scanning for Topographical survey mapping of complex vacant land

Post by landmeterbeuckx »

stutosney wrote: Tue Feb 04, 2020 10:24 pm Hi Paul,

Looks good and interesting you use scanning for topo. Do you not get issues with ground levels where the grass is a bit longer etc? I have just scanned a large topo site myself, all hard standing though. What software do you use to extract the features such as walls, buildings and ground features?

Thnaks,
Stu
I always scan topos, hardly use a total station or gps for a complete site. Gutters, curbs and benchmarks are measured separately as they are difficult to extract sometimes out scandata.

I extract the ground level out of the scans and draw linework etc in either pointcab or riscan. Lines from pointcab are draped onto the surface if needed for 3d linework. Extraction like the use of topodot or Scc is on my wish list but it all comes down to money and investments.
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by smacl »

stutosney wrote: Tue Feb 04, 2020 10:24 pm Hi Paul,

Looks good and interesting you use scanning for topo. Do you not get issues with ground levels where the grass is a bit longer etc? I have just scanned a large topo site myself, all hard standing though. What software do you use to extract the features such as walls, buildings and ground features?

Thnaks,
Stu
It is a good point Stu, if you've got long grass or undergrowth, having a RTK GPS or total station makes a lot of sense. Same goes point clouds derived from drone based photogrammetry, even with decent classification tools for ground extraction in play having ground truthing using a second method of measurement can add a lot of value. Alternative is to mark the boundary of vegetation and exclude from your DTM and contours, but this may not work if the client is doing sections or volumes.

Just an idle thought, but could be interesting to have sphere on a fixed height rod and light tripod to pick up the depth of grass in these situations for some added QA.
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by Jamesrye »

smacl wrote: Wed Feb 05, 2020 8:43 am
stutosney wrote: Tue Feb 04, 2020 10:24 pm Just an idle thought, but could be interesting to have sphere on a fixed height rod and light tripod to pick up the depth of grass in these situations for some added QA.


I had to do this with a Leica scanner, the beauty being that you can fine scan the target and give it an ID. There were manholes in long grass that I knew the scanner wouldn't see.

I do find that deriving a topo from scan data takes a lot longer than using a traditional survey instrument though.
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Re: Scanning for Topographical survey mapping of complex vacant land

Post by steves01x »

We extract large amounts of topo data from scans as well as almost every topo is part of a measured building survey so the scanners on site.

90% of topos are on larger projects so the total station has been out and looped round the site with all the non scan friendly features picked up aka long grass and any holes/drains etc that may need some depth...preferably on non sewage related sites. :lol:

LPaulCook - when you say GPS, do you get away with only measuring the points on the ground with GNSS and no closed loop traverse that is then processed etc before applying to the targets? Our jobs are mixed, some local grid so just the scanner*, others to OS Datum or full survey control through out with 1 second instrument.

**P40 / RTC used correctly in Cyclone Core there are no issues or mistakes... we have done so many 200 to 2000 scan buildings, larger sites with 100+ buildings etc that have had targets everywhere, control inside n out etc... its amazing just how good Cyclone is with good approach on site and good QC as you go through the registration
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