Outdoor Scanning Advice

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Felix_the_Cat
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Re: Outdoor Scanning Advice

Post by Felix_the_Cat » Sat Oct 05, 2019 1:59 am

topogeo wrote:
Fri Oct 04, 2019 9:38 pm
I use a Leica RTC360 on a 2.76 m high SECO tripod
I make pairs of scans 20 meters apart. To the right and left of each I put two targets on a tripod that I detect with GPS. The scans are recorded through the 4 goals that I also use to georeference the group. I put the next couple at 50-70 mt. Each pair covers an area of ​​around 75 x 50 mt .. or even 100 x 70. So to cover 100,000 square meters you should do about 20 -30 pairs. The project will consist of 20-30 separate but georeferenced groups (Leica Register 360 allows it).
The precision is about 2-5 cm but it is a little significant value because the blades of grass distort the DTM ... It is more reasonable to think of a 5-10 cm precsione (..but it depends on the height of the grass ..)
With GPS you are more precise (the pole always rests on the ground) and you put the same time and you have much much lighter data.
In my opinion ..in open land .. it makes sense to use the laser scanner only if the area is a part of a larger project where the scans are really useful ..
100,000m^2

with 40 scans from a low end scanner 10' off the ground

nope
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Re: Outdoor Scanning Advice

Post by steves01x » Sat Oct 05, 2019 11:37 am

It may not be an ideal solution if the job is not local....

If you have a total station... ideally from a closed traverse you could then shoot your targets per each area of scanning. Targets will be referenced as per the processed co-ordinates. Register the scans and shift accordingly then you can view it all together to check coverage, if it needs more go back.


Or a P50 with 1km range from up high on some scaffolding in the middle! :lol:

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Re: Outdoor Scanning Advice

Post by WWilford » Sat Oct 05, 2019 11:40 am

I would second the advice to use a UAV. Set up ground control points if you have any structures that you want to capture in detail with the laser scanner so that you can tie the two together. It will be money well spent.

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Re: Outdoor Scanning Advice

Post by smacl » Sat Oct 05, 2019 1:20 pm

Felix_the_Cat wrote:
Fri Oct 04, 2019 8:50 pm
Hire a drone

Use photogrammetry
Second this, alternatively hire a Pegasus backpack or other SLAM unit that incorporates GPS correction. I've seen a few uncorrected outdoor SLAM jobs that have had substantial errors so would be wary of this in open terrain.

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Re: Outdoor Scanning Advice

Post by matu78 » Sat Oct 05, 2019 1:33 pm

Definitely second the UAV derived point cloud then infills with terrestrial scans and Topo from a total station (long vegetation etc.) It all of course depends on your clients aims and what the conditions are like on the ground. If a terrestrial scanner is essential to use ( if you can’t fly UAVs because of air restrictions etc.) maybe consider renting a scanner in that has a traverse function such as a P40 or MS50, SX10.

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Re: Outdoor Scanning Advice

Post by smacl » Sat Oct 05, 2019 6:20 pm

matu78 wrote:
Sat Oct 05, 2019 1:33 pm
maybe consider renting a scanner in that has a traverse function such as a P40 or MS50, SX10.
P40 would be great, MS50 definitely too slow for scanning large areas and SX10 probably too slow. I get a reasonable number of P40 topographic scans landing on my desk, mostly road and rail, and find the data excellent. If you've got any amount of vegetation, you'll probably also want some check levels with an RTK GPS or total station.

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Re: Outdoor Scanning Advice

Post by LPaulCook » Sat Oct 05, 2019 8:02 pm

I do lots of outdoor scanning of large areas.

I use FARO S350 and X330 scanners, sometimes both at the same time to save time.

First I run control thru the site with my total station survey instrument and set a few, maybe 3 to 10 checkered targets around the site depending on the size of the site and shoot reflectorless control points on each such target. They will be used in my registration as georeferenced points. Depending on the job these points are also tied into NAVD88 elevation datum and tied into the legal boundary monuments to tie the survey into the boundary lines of the site.

Then I start using the scanner(s) and 200mm spheres. I set 4 of them in my direction of my scanning travel and using 1/4 density and Quality 2x. I can set them out 100' or so which gives me 200' distance in my scanning stations. I use a very tall tripod to get a good downward laser shots into the ground. This is very important as if the angle the laser beam hits the ground is too flat no measurement will be recorded.

This setting scans 360° in 2' 40" in gray scale.

I have 12 200mm spheres and different sized checkered targets. I even have some checkered targets I made at 2'x3' and had them printed by FEDEX on PVC boards. I can hit them at well over 500' which is a good anchor for making sure there is no drift in my data.

I added a roof top carrier to carry all these spheres which I keep in padded envelopes and in large padded travel bags with handles for caring them around the site. I use short camera type tripods with flexible legs so they can be attached to fences, tree limbs or magnetically stuck on steel items such as fence or sign posts or on top of parked cars too.

I use 4 spheres in the direction(s) I want to travel in case one does not read well as I have a backup sphere to use for registration. Sometimes a car will pass between my scanner and a sphere at just the wrong time....

I use pretty much the same pattern for laying out my spheres which has not been a problem for me. They should be varied in height and distance and form good strong triangles from the scanner and never be in a straight line.

Your next effort after scanning and registration will be to find the bare earth surface. This is where LiDAR is so much better than drone photographic methods as laser beams can get in between the vegetation down to the earth surface where photographic pixels need much more space to see the dirt. You can either pick hundreds of points where you can see the dirt of get a good program like 3DReshaper that can do that automatically and very accurately. Then 3D contour that surface.

Here's a couple of short videos of large outdoor sites I have scanned and made accurate surface models, topographical survey grade maps.

Watch 9 Hole Golf course fly by, thru and under on Vimeo: https://vimeo.com/337333317

Watch Creek area along the path on Vimeo: https://vimeo.com/271755744

Just so you know: If you are scanning and mapping (3D model) any land, road or any public improvement in California you must be a licensed land surveyor to do so.

There is an exemption for a landscape architect to make a contour map for landscaping purposes only. I'm not sure which state you are in but you may want to check the laws there regarding what is land surveying and what a non land surveyor may do legally.

Civil Engineers can also make topo maps too but they may not establish where lot lines are as lot line establishing (showing on a map relative to any improvements or contours) may only be done by a licensed land surveyor in CA.

This is true for Accident Reconstruction Experts as well. Since scanner came affordable some people are scanning things illegally in California. They may find this out the hard way when there data is not admissible in court, having collected the data illegally.

I hope this was helpful.
L. Paul Cook, PLS
www.LPC3D.com

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Re: Outdoor Scanning Advice

Post by ScottErnst » Wed Oct 09, 2019 2:37 am

Aerial photogrammetry would make this an easy project. With ground control you can expect accuracy in the range of a couple of centimeters which may or may not be good enough. Depending on the ground sampling distance you want it could be flown in an hour or two. There are some caveats. There might be issues with some 107 rules (flying over people, being in controlled airspace, traffic, etc), lots of vegetation will give you a bad model and a featureless surface won't stitch together very well. If photogrammetry will work for you though, it would save a lot of time and hard drive space.

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Re: Outdoor Scanning Advice

Post by stutosney » Wed Oct 09, 2019 4:47 am

If it is open field, you won't still won't get accurate levels using a tripod mounted scanner purely because you won't penetrate through grass etc, especially if it is tall grass. I would definitely go with the drone and if you have solid features such as buildings etc that need to be picked up, use the Faro with targets and just combine the data sets. With open fields, I'm guessing the client isn't massively fussed with accuracy and is more interested in the general layout of the land and a grid of levels, so plus or minus 20-30mm would be sufficient? Have you thought about attaching GPS to a quad bike or something similar and set it to take measurements at intervals? Or set up with a theodolite and get your walking boots on! :lol:

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Re: Outdoor Scanning Advice

Post by Mokeefe » Wed Oct 09, 2019 1:27 pm

Felix_the_Cat wrote:
Fri Oct 04, 2019 8:50 pm
You need to go find a field and do some test scans.

If it is bare ground you have a better shot.

You will be dismayed at how small the return circle is. Vegetation moves. Grass moves. With that scanner on the standard tripod you will likely get 20’ diameter circles of usable scan MAX. Think about how many scans it will take using this process.

An open field is second only to a featureless elevator shaft for registration nightmares.

You will lose your shirt scanning that unless you have unlimited resources

Hundreds and hundreds of scans

Terabytes of data

Weeks of processing time

Hire a drone

Use photogrammetry

Keep your shirt


Sent from my iPhone using Tapatalk
If its just a topography map and you don't need the detail of terrestrial scanner, go for a drone or backpack scanner. It will save you TIME.

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