Using a tracker with a scanner

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Felix_the_Cat
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Using a tracker with a scanner

Post by Felix_the_Cat »

So here is what i am trying to do.

I have an upcoming project where I need to do an interior scan and exterior scan, of what amounts to, well, lets say a fairly large building.

There are three exterior benchmarks and three interior ones that need to be tied into the scans and to each other in as accurately a way as possible.

I will have at my disposal two scanners; a Faro focus 130 and a newer model S. I will also have with me a rather nice Leica tracker.

I have unlimited spheres, and a boatload of SMRs. I have a machine shop at my disposal to make up hardware that I might need.

I have developed a fixture that would hold 4 SMRs magnetically in place as a reference object that may be placed in a doorway, to tie the external and internal measurements together, and hopefully the scans too.

I am looking for the best way to combine the scanner and tracker data.

I am pretty sure my methodology is sound, but I feel like I can't be the first guy to ever want to do this and would like to hear from anyone who might have some suggestions as to where I might look to find a previously developed workflow for something like this.

If you feel the need to post and suggest training, find someone else who has done it and hire them, call me i can do it for you, please; don't bother. And for goodness sakes don't go all Dick Tracy and and hunt me down via social media. I am sick to death of questionable people doing questionable sh!t to contact me directly off this board. But I digress.

So if you have something that might be constructive or collaborative, I would appreciate the insight.

Thanks in advance

Peace
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Re: Using a tracker with a scanner

Post by TommyMaddox »

I've used a system that would work for what you're trying to do and can get you going on a workflow.

Please pm me if you're interested.
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Re: Using a tracker with a scanner

Post by TMillington »

Hi Felix

We use a AT401 Tracker and FX Scanner combination extensively.

We establish sufficient control points using standard 1.5" SMR nests and fix them as a network with the tracker. We then use these - http://hubbsmachine.com/laser-tracker-1 ... 4-pss.html - on the nests to control the scan data.
Often we'll also use larger scanning spheres and/or checkerboards as additional control to tie multiple scans together.

The scans can then be registered together (we use RealWorks and occasionally Spatial Analyzer, but the principles are the same for most registration software) and finally 'georeferenced' to the tracker points.


Cheers

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Re: Using a tracker with a scanner

Post by PHughes »

Hi Felix

I have quite a bit of experience using a Laser Tracker to control the layout of your scans. Although I am not using the Leica kit but the API Laser Trackers the workflows you can use are all the same and really comes down to setting up the control network right.

I have used several methods to result to the same control point including measuring the spheres and targets just using the SMR and additional tools. You can get some nice conversion tools that result to the same centre point as the spheres which makes it nice and simple. If you have a machine shop at your disposal you could make a load of pucks that you can fix to the building that will house the sphere magnets, then make yourself a offset nest that holds the SMR at the same height as the spheres and also centres in the same pucks. With that setup you can quickly replace spheres with the SMR and link all the measurements together.

Measure you target locations into SA/Verisurf/Metrolog and export that as a control file (CSV), this can then be imported into Faro Scene and used to place each scan.

Alternatively we use Geomagic Design X and import and align the scan data there to allow a quicker workflow to start creating CAD models.

As long as you have a solid network setup throughout the building you should be good, thinking about the shooting the laser tracker through doorways might limit the angles you can produce but that's the only way. Also if there is a big contrast in temperature or airflow between the outside and inside when you are shooting the targets that might have a small effect but I think based upon the scanners accuracy that wont be an issue.

Sounds like an interesting project, hope it all goes well.

Good Luck :)

Patrick
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Re: Using a tracker with a scanner

Post by Felix_the_Cat »

Thank you kindly for the replies. This place is awesome when it works right.

I need to ruminate a bit on the information provided, so I can spare you from stupid questions.

As added information, I have scene, SA, and too many CAD packages to list. Cyclone is coming, but it is currently languishing in the corporate procurement process and may or may not show up in time. I'm off to SA training in sunny SoCal next week (Yeah sun! Yeah warm!) Hopefully those folks will have some helpful hints too.

Thanks again for your help.
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Re: Using a tracker with a scanner

Post by NOVAMECH »

My Question is - Why do you need to use a TRACKER - when scanning a building? You are talking sub millimeter accuracy here. Where as you scanner will at very best provide 2mm to 4mm accuracy.

NOVAMECH has an Leica AT402 plus a Leica 1205 reflectorless Total Station. 2 Terrestrial Scanners.A Romer Absolute Arm

Unless I was Scanning a Large AirCraft - combining Romer Arm Scan and Probe data of detailed areas with - say, terrestrial data on the outer skin.

I can't really see the need for a TRACKER to control a Building scan - Sounds like you are spoilt Rotten at Lockheed Martin. Ha-Ha.
Maybe you have to many tools and cad packages - each one of these requires extensive maintenance and training to use effectively.

Please, do tell WHY you require sub millimeter accuracy on building? - Recently, NOVAMECH scanned a large Turbine Power Station, for GE - Our closed control - was 1mm,1mm and 6mm on the vertical - which was because a mistake was made. Or that was what we deduced, and was totally fit for purpose

We used minimal targets and used Cloud to Cloud. ZF Laser Control.

Upon Check - our cloud to cloud was better then our closed loop survey - go figure??
I was telling the German Surveyor, that we did not have enough targets and this is not the way I would do it. I thought we were going to have major problems on Registration
However, He was a registered surveyor in Germany. So I did not push my luck.

I was amassed that our C to C - turned out better then his Control Survey with the Leica 1205.

My Tilt and Turn Targets are gathering dust as I write this.
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Re: Using a tracker with a scanner

Post by Felix_the_Cat »

Hi Nick,

Thank you for the reply.

The idea here is twofold. The benchmark measurements plus a few other key elements measured will be exclusively tracker, and require tracker accuracy. They are for seriously tight alignment duties.

The scan is a general survey of a large space, and the equipment therein. The goal is to provide a baseline for future equipment installs, to negate the need for multiple people to travel to ugly places every time a new flavor of the month pops up. So I get to travel to ugly places instead, because I am, um, more able to roll with it, shall we say. Most of the new stuff just needs scanner accuracy for placement. A few things will require tracker accuracy, and because they don't exist yet a general idea of their requirements is all that is known. so i need to be as close to real as I can in those areas, for future use.

My scans typically are close quarters, through what amounts to long 3' wide hallways that chicane in crazy ways; hundreds of linear feet with double reverse hairpins in multiple spots.

Despite my best efforts, and an insane amounts of spheres, the close quarters and switchback nature of the topology leave me open to error. I have not been able to nail down if it is hinging or lateral error. But I have been experiencing as much as 1" of error per hundred feet of scanning, This is no good. Sorry Faro, I'm looking at a surphaser now.

So what I am after is a more accurate way of registering the scans, or at least of tying the scanner data and tracker data together more reliably in those areas where I need the higher accuracy, and being able to back measure to the benchmarks. All for future use.

Yeah, I'm spoiled with the CAD and equipment. But I also have to produce, or somebody else will be posting here.

I'm sure you know the feeling.

Thanks again for the insight

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Re: Using a tracker with a scanner

Post by mls »

Surphaser route sound like the right one if you are working in the metrology and inspection types of project . A little more effort, but far superior data. We have evolved a similar workflow to the one you describe , and based on using tracker, CMM / line probe, and Surphaser. Its large scale metrology.
Software including Scene, Geomagic(s) rhino, pointools (old edit), Arena 4d, cloud compare, polyworks, and Inventor.
My experience gathering data sounds similar also and has got me into some very interesting places.
I'm not sure public forums are always the right place to discuss specifics, and some of our clients might not be too pleased if we did, so if you want to swap experiences please PM me.
Cheers
Paul
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Re: Using a tracker with a scanner

Post by NOVAMECH »

WOW - Sounds like a surveyors Nightmare - And I'm not one. However, Sounds to me you need more
References within your environment to be able to use a C2C Reg. I have come to use a combination of C2C and control on all my projects - after some 8 years of experimentation.

Have you ever tried - stick on CONES? or stick on rods? Some software allows you to create geometric surfaces - Therefore you will be able to create a control point at the cones tip. Or at just at the tip of a control Rod.

I sometimes create control points - Vistula within the scan data - Like the tip of a rod. If the diameter is say 6mm and you have some common scan point along the rod to the tip - just create a control vertex a the tip and you with 6mm or better.

A combination of control point and C2C works very well.

Using a TRACKER to control would add - days to a scan project. And I might even make a mistake during the process over this time frame.

You do not have to rely on Software to create Control Vertex point - if you have say a common Rivet - This can work - or a crack or dimple on a wall. Change in intensity - like a White Dot on a gray or darker wall. Black dot on a white wall not so much.

Cheers Nick
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