3D for Crazies

[10bulls]

When I first read this thread I thought senility had finally overtaken you greybeard. But who am I to judge! So in the spirit of experimentation...

Photo'd green man in a tray with blue food colouring (I think my hands may be stained for life!). I photochopped it a bit and made background blue.

OK, then I made a copy using only the RED channel. (If you've ever read 'The Deep', there's a good bit about the colour of blood at various ocean depths).

This last image was then stuffed into the CamBam heightmap plugin and hey presto.

Greybeard, you are quite possibly a genius!
Now all I have to do is persuade the kids to stay still under the bath water long enough while I go get the blue food colouring.

[epineh]

Looks like we need to go trade in all 3D modelling software for some trays, milk and assorted food colouring...

Hey John, are you the same Greybeard that has Blender tutorial videos on the Blender homepage? ... seems a strange coincidence.

Russell.

[greybeard]

Not me, unless there's something about me that even I don't know yet

I downloaded blender two years ago, but haven't unzipped it yet - perhaps it's time I did !

John

[epineh]

Ah well it was worth a try, and I was hoping to get some free lessons !!!

It is actually a fairly capable program (and free!!!), though I am not at all any kind of expert on 3D modelling, it seems reasonably useful to me, I'm sure I read somewhere it exports STL files if needed, I'm thinking of using it instead of AutoCad, since I have to learn from scratch anyway.

Currently downloading what tutorials I can find, I think it could be used to incorporate laser line profiles from a series of photo's / movie frames... I just have to figure out how to make SOMETHING first...

Russell.

[greybeard]

Hi Russell. I too have started on it. I've tried a few others before, but realise that some serious study is now necessary.

John

[greybeard]

I've had another idea quietly brewing in the background which may appeal to those to wish to avoid total immersion in asses milk, or whatever.
The set up is extremely simple (always a dangerous sign) and I make no attempt to offer the software, but I would be interested to hear of any views on its feasibility, details of constructional improvements, and any offers of programming if it does seem worth pursuing.

The device is a laser "probe" that would be attached to a cnc spindle, for example, as a way of providing the x and y data.
Its construction (see diagram) consists of a laser pointer which can be "rocked" back and forth some 1.5 degrees to produce a short line of light on the surface of the target, some 10" below.
Looking vertically down through a pair of aligned pinholes onto the target is a photo receptor of as yet undefined quality.

The method of rocking the laser pointer also outputs a signal which is proportional to the movement, such as a pulse train.

When the laser spot is visible to the receptor, a count of the pulses from the zero position of each "scan" gives a number proportional to how far across the spot moved from its starting position. But within the limits of this simple setup, with a very small angle of scan, this will be proportional to the increase/decrease in height of the target at that point, each new measurement relating to the previous one.

John

[10bulls]

I've had another idea quietly brewing in the background

I don't think this will work John. You are wobbling the laser in one plane and are assuming that light will reach the pinhole detector (located in the same plane) at some point during the lasers cycle.

Problem is, the scanning surface is just as likely to reflect light either side of that plane (i.e. infront of and behind the plane of your diagram).
You'd just get the odd pulse when the laser happens to be reflected in the same plane as the detector.

No, I'm afraid if you are going to be seduced by the sparkle of the laser, you must also accept that a camera of some sort will also be needed.

[greybeard]

Good point.
I had assumed that whatever the angle the surface was, the photodetector would "see" the spot made by the scanning beam when it was below the pinholes.
I'm leaving out any considerations of resolution at this stage.

I did leave out a detail in last night's posting that the beam's zero position for each scan is the base plane of the target, directly below the pinholes. The maximum scan position would be to a point that would represent a 2" height, hence the 1.5 degree limit of its travel.

Perhaps I'll try it, if I can find a detector, or perhaps soomeone else could, if they have the kit ?

EDIT
Having had my breakfast coffee, sense has prevailed. If the resolutioin was 1mm, and it stepped once per second, it would take about 3 hours to scan an area 4" x 4".
Back to the asses milk, and improve my depth of field setup.

[10bulls]

Good point.
I had assumed that whatever the angle the surface was, the photodetector would "see" the spot made by the scanning beam when it was below the pinholes.

Thinking about it again this morning, you may be right. I guess unless the surface is smooth/shiny you'll get some diffused light reaching the detector
(I've read coating objects with powder helps)
I wonder how laser ranger's work? (Don't make me google this early in the day!)

[10bulls]

Re: Asses milk:
I quite like this method, but there are a number of drawbacks.
. The object needs to be uniformly the same colour.
. The object needs to be uniformly lit (without getting specular reflections on the surface of the liquid).

I have a bottle of blue lamp oil. It's for lamps. And its blue. Oh yes, It's made of oil.

If I paint an object with water based paint, then put it in the lamp oil hopefully the paint won't dissolve in the oil. This may increase the difficulty of making 3D scans of the kids though...

Step 1 (paint kids with white poster paint)
Step 2 (into the bath of blue oil)
Step 3 (trying to avoid this...)

[greybeard]

Last thought before I go out to chop wood etc. - It seems like a compromise between the range finder and an ordinary scanner. Somehow get the scaner to use a laser line insteadof the light bulb, and change the scanning mirror to look down at an angle instead of straight down.
Ho hum, off to work.

[epineh]

It would be nice to "hack" an existing scanner to do this kind of work, but I can't imagine where to start. If you could seperate the data from each individual line as it scans, with the laser at an angle to create a profile. Looks like some serious googling is in order... and I was going to have an early night.

Maybe just make the scanner tray waterproof to hold milk lol

Russell.