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Posted: Sun Jun 15, 2008 10:08 pm Post subject: Questions about 3D laserscanning
Hey,
I have some questions about 3D laser scanning. I've searched on the internet, but is defficult to find information about it:
question 1) What's the difference in accuracy and range of laser scanning devices: time-of-flight and phase-based
2) Can i scan snow, water using a laser scanning? how does this type of surface affect the laser scanner?
3) are there any problems using the scanner when scanning in the dark or scanning in light invernoments?
Posted: Mon Jul 07, 2008 11:26 pm Post subject: Scanners
I have been scanning for an engineering firm for 3 years. Time of flight scanners give you longer range with longer scanning times. We have a Leica and it is around 4000 pts per second. Manufacturers all have different specs but for the most part around 300m, but I will never do that. Takes too long and there is too much noise involved with the data. The phase based scanners are around 5000,000 per second but only have a range of around 30m. I was stuck in a snow squall and the scanner will scan snow. It wound up looking like a firework. We have scanned water just b/c it fell within our scan, and it wont pick it up. We work in a lot of train and subway tunnels and it will scan in the dark. The problem you encounter is making sure you and your crew can see the targets in the dark and you frame out what you actually want to scan. Some things to think about, dark surface, black, dark red, dont scan real well, and neither does some type of flashing or trim. Most salesman will give you a demo. I dont know what part of the country you are in, but we did a real world demo in NYC. We own 2 a Leica and a Trimble. Since we took delivery of our Leica ScanStation, our Trimble has sat in the case in our equipment room. Hope some of this helped.
Posted: Tue Aug 19, 2008 7:17 am Post subject: 3D Scanning
I'll add some feedback too:
yes the scanner will scan snow and water. I've picked up snow, blowing and falling and rain in scans. As for ground cover we pick up really good returns from snow! Water yep we can get water too, as mentioned earlier water can be tricky. The higher the angle of incidence the better return you get from water. A low angle of incedence can actually produce a reflection below the surface. One time I was scanning an area that had an asphalt parking lot and got reflections below the parking lot, it was kind of cool once we figured out what it was.
Scanning in the dark works really well, the only problem is finding the targets in a dark photo, but that has a work around too.
1) Depens on the sensors of your scanner, you can look it up in the manual. In theory it sould be easyier to get an accurate measurement of the phase than on the time of flight.
2) Scanning water is not easy as the laserbeam must be reflected back to your scanner to get a measurement. Snow reflects the laser in a diffuse way so it sould be possible to 'see' it with the scanner, but the scans wont be accurate since the light is not reflected on the surface but goes under it and is reflected there. So if you want to get measurements on water be shure its not cristal clear or you will not get a reflection back to your scanner.
3) The darker, the better. Ambient light can disturb scanning results.
Continuing the topic - I'm struggling to find information or experiences with the overlaid digital photo function for scanning in general. I do not use the equipment myself, but am rather an end user. I've seen a 3D model animation, but it was an animation of the point cloud file converted to ACAD - it did not have any digital photo information and thus, was impressive in it's detail, but not realistic looking.
My end goal is to provide a finished animation of my design - using the design CAD files themselves and not just some type of 3DS Max creation or Viz creation. I realize I'll convert my Civil 3D 2010 design into 3dS Max or some other software, but I'd like for the proposed renderings to include existing condition renderings that look accurate. If the 3D scanning equipment can overlay a digital photo, can that ability be applied to a rendering? It sounds like this is possible based upon the advertisements of the manufacturers, but I have yet to come across any examples or individuals who have accomplished this. My thought is that you have people who focus on the surveys, and people who focus on the designs and they use different software and different approaches. Combining the two for one solution seems feasible, I just haven't seen it yet.
Posted: Wed Jul 08, 2009 3:39 am Post subject: Photos on Laser Scans
mockymock- The scanner than I use has the capability to capture photo textures when it scans however it isn't industrial strength. If you take a look at the image below you can see the photo texture applied to the model of a skull.
The scanner takes a photo of the object from the same angle as the lasers and applies it to that specific pass of the scan. When several passes of the scanner/camera have completed the textures are blended together and wrapped around the object.
The entire scan can then be exported as a file type which supports textures such as OBJ or 3DS. I'm not sure if your CAD software will accept these formats.
Posted: Wed Jul 15, 2009 6:31 am Post subject: Re: Photos on Laser Scans
[quote="Pangea3D"]mockymock- The scanner than I use has the capability to capture photo textures when it scans however it isn't industrial strength. If you take a look at the image below you can see the photo texture applied to the model of a skull.
The scanner takes a photo of the object from the same angle as the lasers and applies it to that specific pass of the scan. When several passes of the scanner/camera have completed the textures are blended together and wrapped around the object.
The entire scan can then be exported as a file type which supports textures such as OBJ or 3DS. I'm not sure if your CAD software will accept these formats.
Thanks Pangea3D - Was doing this particularly difficult and or time consuming above and beyond the normal scanning time requirements? Of course I'm trying to get it done for the exterior of a building but I don't need microscopic detail, I simply don't want a bunch of gaps in my 3D model of my site. Most of what I've seen is applying a proposed 3D site design to a Google Earth photo or aerial photo - which looks nice but has some limitations. I was hoping these 3D laser surveying equipment could record a site and map the digital photo's in a fairly painless effort. 3DS format is fine - it's what I expect to export my ACAD model into.
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