Any experience scanning footprints in sand?

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Simon.
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Any experience scanning footprints in sand?

Post by Simon. » Wed Aug 31, 2016 9:41 am

Hi all, new to the forum, but can't find any discussion regarding to scanning a footwear impression in quite sandy substrates. I'm a Forensic student from Perth in Western Australia, and our soils are super sandy, so when we get impressions, they can't be cast, or measured in any way other than photographs as a general rule.

I'm putting together a kinect-based scanner as a project, as well as using a Faro Freestyle to scan some impressions and see how they measure up, but don't particularly expect to get great ridge detail on the prints. Does anybody have any experience measuring impressions either in sandy soils, or with specific devices that could offer some advice on the best device or technique to use?

I'm aware better scanners exist for fine detail scanning (like the Artec Spider) but I have a pretty limited budget to go on unfortunately.

Thanks!

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Re: Any experience scanning footprints in sand?

Post by MStrahan » Wed Aug 31, 2016 9:50 am

Have you considered using photogrammetry? It's often the cheapest way to go for non-contact digitisation and can yield pretty good results if you take enough quality images for the software to work with.

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Re: Any experience scanning footprints in sand?

Post by Simon. » Wed Aug 31, 2016 10:16 am

Haven't considered it to be honest! I'm not actually just focusing on footprints with this project, it will just be one of the more important factors. I will be doing other evidence types, as well as just general scene capture. And also, I am limited in time and don't want to get too far into different methods. Do you know what kind of quality/accuracy in detail you could get from photogrammetry on a footprint?

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Re: Any experience scanning footprints in sand?

Post by MStrahan » Wed Aug 31, 2016 11:12 am

The results you get will vary from software to software. I've experience in using Agisoft Photoscan, which I've found to be pretty good. I understand Visual SFM can give good results as well. If I recall correctly, Autodesk's Recap can do photogrammetry as well as scanning, but it's more of a black box system that gives you less of the fine control you can get with Agisoft and VSFM. That said, I don't have too much experience with it so I can't say anything definitively.

One thing to remember with photogrammetry is that the results will not be accurately scaled unless you include an accurate scale bar/ruler in the capture on site. If you don't do this the scale of the resultant model will be entirely arbitrary which can lead to some confusion further down the line if you're not aware of it.

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Re: Any experience scanning footprints in sand?

Post by max72 » Wed Aug 31, 2016 1:16 pm

http://www.laserscanningforum.com/forum ... 06&t=10088

Snow, not sand.. but I guess they can be assimilated.

Consider Eugene is a guru, so what looks easy in his hand might be a challenge and for sure a top level benchmark..

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Re: Any experience scanning footprints in sand?

Post by 3DForensics » Wed Aug 31, 2016 1:46 pm

Hi Simon,

Welcome to the forum. I particularly like photogrammetry for footprints because it's just so practical. I also experiment with a lot of other methods. For example, this grave was created from a small iPhone video (120fps) walking around the grave. You don't get the same high resolution detail as a high res DSLR camera, but it's definitely good enough for grave documentation and evidence location.
Clipboard01.jpg
Clipboard02.jpg
As for footprints in sand, using a good lens on your DSLR is a key factor as is a steady tripod with a wireless shutter remote to minimise any possible movement. Also, you need to establish a very good scale by using a ruler that has very discrete points of reference like two checkered targets or something with a sharp corner.

Since you are likely going to be dealing with a lot of sun, you should also consider using a small canopy to shield the sunlight and create a strong diffuse environment which is the best for capturing photos and details.

Here are a couple of shots of students who captured their first footprint...there is room for improvement.
Clipboard03.jpg
Clipboard04.jpg
What are you going to to do with the footprints once you've captured them in 3D?

Cheers,

Eugene
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Re: Any experience scanning footprints in sand?

Post by Simon. » Wed Aug 31, 2016 3:24 pm

Thanks Eugene, those footprints look pretty good! I wish we had nice substrate like that here! Once you've captured your images, do you have any software/website that you recommend for the processing? Once we've got our footprints, the aim is to get the data easily working with WA Police systems (Mostly FARO Scene and AutoCAD), and to recreate them reliably with the 3D printer for courtroom comparison and presentation. The main point of the project was to show proof of concept with a low cost kinect SLAM device, but I'm working with the police to aim it towards their current needs (funding for new toys essentially).

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Re: Any experience scanning footprints in sand?

Post by 3DForensics » Wed Aug 31, 2016 3:40 pm

With all due respect, I think you shouldn't waste your time with Kinect or even a SLAM device. You won't get what you are looking for...I am speaking from experience :)

Photogrammetry is the way to go. You should be lookng at PhotoModeler, PhotoScan and similar programs.

They also will produce a mesh that is partially ready for you to print. You just need to close the volume in another program like Meshmixer or similar.

Cheers,

Eugene

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Re: Any experience scanning footprints in sand?

Post by 3DForensics » Thu Sep 01, 2016 2:18 am

And this is the mini 3D print.

Image


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Re: Any experience scanning footprints in sand?

Post by Simon. » Thu Sep 01, 2016 10:08 am

3DForensics wrote:With all due respect, I think you shouldn't waste your time with Kinect or even a SLAM device. You won't get what you are looking for
That's what I expected unfortunately, however the games design guy I'm working with wants one for his lectures so he's building one regardless! I have been saying from the start that it won't get anywhere near the detail needed for forensic evidence. But it might give us a good cheap alternative for 3D mapping small scenes in outback towns (in WA we have a lot of very remote towns), when the main surveying teams don't need to visit. I hadn't planned to add photogrammetry into the mix but may as well as I have everything necessary, bar the software, but that shouldn't be an issue.

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