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 from about 1.13 onwards Zachary Seldess is using plane culling to cut out a specific area of the kinect view. I am trying to achieve the very same thing using the depthmap of jit.freenect.grab. Any ideas how I might go about achieving this? what objects might I have to employ? Many thanks :)

In this video from about 1.13 onwards Zachary Seldess is using plane culling to cut out a specific area of the kinect view. I am trying to achieve the very same thing using the depthmap of jit.freenect.grab. Any ideas how I might go about achieving this? what objects might I have to employ? Many thanks :)


plane-culling-with-the-kinect

First, perhaps consider more modern externals for connecting to the Kinect. For example, jit.openni or dp.kinect. Even synapse.

With either jit.openni or dp.kinect, you can use the body detection -and- the logic it uses to ignore non-bodies (chairs, floors, walls, etc.). You can find "players" with the same code and use it as a filter to only show parts of the depthmap that have an identified player. Lots of rich things.

If you don't want to use the human body detection, then the depthmap you get from jit.openni and dp.kinect is already in true world depth. So the 1-plane matrix you get therefore has 3 pieces of data (x-coord, y-coord, true world z depth). And, there is no undistorting to do with dp.kinect or jit.openni. Z is true Z unlike other technologies out there.

Given that there is a true Z, you can use math objects like (jit.op) to filter out any Z values that you don't want. Leaving only the interesting ones. If you want to filter by X or Y, use objects like (jit.expr) to black out (set values to 0) the rows (y) and columns (X) that you don't want.

Hi Dale, thanks very much for the reply. I don't want to use the human body detection as my system needs to be able to detect anything waved in front of it. I am effectively trying to build a distance sensor, you move something closer towards the kinect, the notes triggered get higher in pitch. I had been using `[jit.op @op ]` to extract a "slice" and then look for movement within that slice. I can't seem to get this process working with jit.openni. Here's an example patch:

I'm also wondering if this is the best way to do this. I have set up a system that extracts 8 slices and then triggers a MIDI note when movement is detected within them. Is this the best way to do it? I just can't help thinking that there is a super elegant way of achieving this! Here is the patch I had built with jit.freenect:

A few things come to mind as I look at the first patch with jit.openni.

You had jit.openni outputting longs (the matrix type was long for the first outlet) and the distmeter was set to 0. Therefore, the depthmap was reporting mm. On the right side of your patch, you then used two jit.ops with 0.8 and 0.795 are comparison values. Meaning comparing 0.0008 and 0.000795 meters. You will have no reliable success with trying to slice only 3/4 of a mm. I doubt that's what you wanted. ;-)

While the Kinect does measure in mm, its stability in readings won't be that precise and consistent. They also become less precise as you get further from the Kinect. Perhaps look at slices in the 1-2cm range near the Kinect and larger slices further away.

Unless you just love mm and working in integer math, I recommend you switch your patch and thinking to meters and floats. Personally, I do that in all my work now. The patch I've attached below does that. (Also, the patch below uses dp.kinect. That object is outlet compatible with jit.openni. However, some of the attribute names are different. You will find equivalents. I think in this case, you will only need to remove @depthmap since that config is done via the XML file on jit.openni).

I didn't fully understand the intention in your smoothing subpatch.  I leave that to you.

Your a star Dale, thanks very much for helping me with this! :)

Plane culling with the kinect