Print 3D Images to Scale

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dan574
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Print 3D Images to Scale

Post by dan574 »

Hi All,

As they say long time listener first time caller. Ive been lurking for a while gathering lots of useful information from you guys.

Im a collision investigator with the Victoria Police in Australia and we have recently acquired 2 Riegl VZ400i's.

We are progressing slowly and at this stage we are using Risolve only.

Just wondering if anyone knows of any software that will accept the point clouds and allow us to print 3D views to scale?

Thanks in advance.
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Re: Print 3D Images to Scale

Post by 3DForensics »

Hi Dan,

Welcome to the forum. Riegl has been very well represented on this forum and you'll find David Foster, Domenic Raneri and a few others to be a valuable resource for you since they are also Riegl users.

To answer your question, it is easier to take a laser scan model and create an orthographic image from it. This is like a top down view that is scaled. I am not a Riegl user myself but I am almost certain that they have this ability in either RiScan or Risolve. Basically, you would end up with an image where each pixel represents a certain amount of distance like 5cm or 10cm...something like that.

Now, if you were talking about using a perspective view, that is much more complicated since you can't equally scale for the whole image but only a single plane in the image...this, I have never tried.

Cheers!

Eugene
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Re: Print 3D Images to Scale

Post by dan574 »

Hi Eugene,

Thanks for the reply. Ive had the pleasure of meeting Dave and Domenic and they provided some awesome information.

I'm no where near their level and am learning as I go.

Im able to a top down view to scale in Risolve.

I was thinking of a scaled perspective view.

Dave isn't aware of any program so I thought I would throw it out there.

Thanks again
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Re: Print 3D Images to Scale

Post by 3DForensics »

The problem with perspective view is that the scale changes according to the distance from the camera. So, it's not a "fixed" view.

You could potentially place a 3 dimensional scale in the image at a certain point to give you a sense of scale. This could show each of the axes directions and the length of each axis indicator could be a fixed distance (1m, 5m ....etc.).

Cheers,

Eugene
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Re: Print 3D Images to Scale

Post by d.raneri »

Hi Dan,

I think that Eugene's explanation is the only way to "scale" part of an image when viewed in perspective mode, though the scaled plane should be perpendicular to the camera view. It's not great practice, as not everybody fully grasps the difference between orthographic/perspective images and it could lead an investigator to make an erroneous measurement elsewhere in the scene.

Do you have an example of what you're trying to achieve in this particular case?

Dom.
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Re: Print 3D Images to Scale

Post by d.raneri »

Most software will have a feature to render high resolution perspective images. RiSolve can do this if you right click blank space in a view window and select Save Image. You can then set the image size, resolution, etc.
Image

The problem with measuring from perspective images is that the apparent size of an object changes based on distance from the camera, as Eugene mentioned.

Here's an orthographic image, which shows that the lengths do not change as they move away from the camera.
Image

This perspective image is quite difficult to measure from, as the grid blocks get smaller toward the back of the image.
Image

As Eugene suggested, you could introduce a scale into a perspective image, however this brings about its own challenges. This is quite easy to do in the Maptek software we use (though I'm definitely not recommending you run out and buy it haha). You could do this in RiSolve by modelling a scale using something like Blender (free software) and then importing it. You can see in this image that the included scale gets smaller as its length progresses toward the back of the image.
Image

If you were to "scale" or measure directly from a perspective image, you would need to have the camera face the plane of the scale at 90°. Again, this presents two problems. Firstly, the measurement couldn't be over a very large area, such as a roadway. There will be some perspective distortion introduced at distance from the focus point/image centre. Secondly, you run the risk of somebody applying the scale to the wrong plane. In this example, you could use the scale to measure along the front wall (green arrow), however you could not use it to measure from the back wall (red arrow) because in perspective mode, the size changes as you get further from the camera.
Image

In this orthographic image, however, we can measure both the back and front walls from the same scale because the size remains the same, regardless of distance to the camera.
Image

Effectively, I would stick to using orthographic renders for measurement. But again, if you have a specific example please do share and we'll see what everyone comes up with!

D.
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Re: Print 3D Images to Scale

Post by 3DForensics »

Excellent post and examples Dom!
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Re: Print 3D Images to Scale

Post by Dave Foster »

3DForensics wrote:Excellent post and examples Dom!
That saves me a whole load of time after Dan asked. This wasn't something I thought would be needed - I would record measurements in a view from either RiSolve/RiScan, or probably better on the eye in Veesus. The screen shot wouldn't be to "scale" as mentioned as that is affected by perspective already outlined. In ortho mode they would look bizarre. But I see how the scale could work. Cheers, Dom!

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Re: Print 3D Images to Scale

Post by 3DForensics »

Dom,

Are those images from a case you presented a while back at IAFSM?

Eugene
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Re: Print 3D Images to Scale

Post by d.raneri »

Eugene,

They're from our crime scene training facility. You would have seen them in something at FSM as they're pretty much the most family-friendly scans I have, so I tend to use them quite a bit for various things haha.

Dom.
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