ARKit: Plot a Node at a specific pixel at a specific Z distance from Camera

问题

Referring to the image above. I have a Red Node at the center of the screen with a distance of 1.0 unit (1 meter away) [See iPhone Portrait Top View]

What I do is I capture a screenshot of the iPhone screen and the resulting image is 750 x 1334 pixels [See iPhone Portrait Front View]

sceneView.snapshot()

What I want to do is put 4 Red Square Nodes located on the four sides of the iPhone screen relative to the Red Circle (at the dead center of the screen). I am making this to mark where I did a snapshot. What I want to know is how can I plot a box node precisely at a certain x,y point given z distance. (The value of Z is not fixed, I just used 1.0 as a sample scenario).. I want to plot (0,0), (750,0), (0, 1334) and (750, 1334) at a given z of 1.0 and assuming I am on a tripod, the plotted nodes would appear on the four sides of my iPhone screen.

I am very terrible at math and this problem is so complicated for me to solve alone with my current math skills. Can anyone help? Please?

回答1:

Since you need ARnchor nodes (to mark where a snapshot was done) using the real time information from the camera instead of a snapshot would be probably easier. In special due to pixels in a 2D image are referenced from left to right and from top to bottom (with "0,0" coords located in the top left side) ... and we know the AR nodes are referenced in 3D coordinates with the center of the local node as the 0,0,0 coords.

I haven't yet code to test but I think the following properties should help:

    let pPoint  = sceneView.projectPoint(self.centerBall.position)
    let fieldW  = sceneView.session.currentFrame?.camera.imageResolution.width
    let fieldH  = sceneView.session.currentFrame?.camera.imageResolution.height

The "pPoint" should return the 2D coords corresponding to the (0,0,0) 3D coords of "centerBall" from there it should be just add or subtract calculations to obtain all 4 corners in 2D

Finally passing the 2D coords of every corner to the "unprojectPoint(:)" method should provide the 3D "world" coords and that can be converted to "centerBall" coordinates with the "convertPosition( position: SCNVector3, from node: SCNNode?)" method

It seems interesting so will try to code this before weekend

At the end I suspect ARanchor nodes may not be 100% stables

来源：https://stackoverflow.com/questions/51015711/arkit-plot-a-node-at-a-specific-pixel-at-a-specific-z-distance-from-camera

标签

swift

nodes

arkit

pixels