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### Topics - Shizzn

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##### Support / Vuforia - Position and Rotate Objects with Model-View Matrix
« on: December 21, 2015, 08:37:04 pm »
Hi guys,

I want to share my solution to the problem of positioning and rotating 3D-objects from jPCT-AE with OpenGLs Model-View Matrix (e.g. Vuforia tracking data) because I was asked to give help concerning this topic.
A picture of the Model-View Matrix and its components is attached. I created this picture as a part of my bachelor thesis.

A little warning:
I haven't used jPCT-AE with Vuforia for more than 2 years
Furthermore, the code snippets are simpified.

You can get the Model-View Matrix by tracking markers with the Vuforia SDK. The tracking data will be used to show 3D-objects on the marker:

In the onDrawFrame-Method I apply the origin (position) of the Object3D-object via a SimpleVector by using the Translation-Vector of the Model-View Matrix
Code: [Select]
`mSimpleVector.set(modelViewMat[12], modelViewMat[13], modelViewMat[14]);myObject.setOrigin(mSimpleVector);`
After that I apply the rotation by converting the Model-View-Matrix float-array to a RotationMatrix:
Code: [Select]
`myObject.setRotationMatrix(ArrayToMatrix(modelViewMat));`

Code: [Select]
`protected Matrix ArrayToMatrix(float array[]) { // Declare variables float[] insertDump = new float[16]; // The array holding the values in // the new Matrix int targetElement = 0; // Points to the next location in the insertDump // to add data // Loop through the rows of the Matrix3f for (int sourceRow = 0; sourceRow < 3; sourceRow++) { // Insert the 3 elements from the Matrix3f into the Matrix. The // fourth element has been initialized to 0.0f. insertDump[targetElement] = array[targetElement]; insertDump[targetElement + 1] = array[targetElement + 1]; insertDump[targetElement + 2] = array[targetElement + 2]; // Move the target ahead by four spaces targetElement += 4; } // The final row consists of { 0.0f, 0.0f, 0.0f, 1.0f }, since this is a // rotation matrix insertDump[15] = 1.0f; // Create the new Matrix and load in the values Matrix output = new Matrix(); output.setDump(insertDump); // Return return output; }`

In my finished project I have a two-dimensional array of 16 Model-View Matrices, so I can place 3DObjects on up to 16 Vuforia Markers. That's why my original code would be too complicated.
My project, which I developed as a part of my bachelor thesis, shows 3D-Letters on the markers, so that the user can put them together to an existing word. (see the following YouTube-Link)

If you have more questions concerning that topic, you can ask me. But I have to repeat my warning: I haven't used jPCT-AE with Vuforia for more than 2 years
If any important information is missing, please tell me.

Happy coding
Shizzn

2
##### Bugs / 3ds-File Import - Pivot-Point not working
« on: September 01, 2013, 04:56:46 pm »
Hi Egon,

in my jPCT-AE-Project, I try to import an 3ds-object (created with Blender), but the pivot-point of the 3ds-file is not imported/converted. As you might remember, I use Vuforia for the tracking of a marker and need jPCT-AE to set the Rotation and Translation of 3D-objects. The objects are displayed correctly, but some of them (in my case the objects are 3D-Letters) aren't in the center of the marker because the Pivot-Point in jPCT-AE is not in the center of the object. So, here's my Bug-Report:

Bug: The Pivot-Point of an imported 3ds-object is not converted to the Object3D-object.

What did I try to solve the problem?
• change Config.useRotationPivotFrom3DS
• scale the object with Blender (instead of jPCT)
• check the Pivot-Point of the 3ds-object with 3dsMax

What's the effect?
jPCT-AE doesn't take the Pivot-Point of the object, but the center of the bounding box of the object, even if Config.useRotationPivotFrom3DS is true. The difference is shown on pivot_bug_1.png in the attachments: The Pivot-Point is marked with big arrows. The center of the bounding box is marked with the coordinate axes.

What's my workaround?
I load the objects via Loader.load3DS (doesn't matter, whether Config.useRotationPivotFrom3DS is activated or not) and set their RotationPivot-Point (setRotationPivot) to (0, 0, 0). Then, jPCT-AE does not take the center of the bounding box, but Blender's world center. This can be seen on pivot_bug_2.png: The Pivot-Point is little 'yellow' dot with the arrows. The world's center is in the middle of the crosshair.

As you see, I checked many cases and tried several scenarios. One of my biggest concerns was, that Blender does not export the Pivot-Point. But as mentioned earlier, I imported the 3ds-object with 3dsMax, checked the Pivot-Point and realized that it was at the right position. That's why I think, that jPCT-AE does not import the Pivot-point of the object correctly.

Greetings
Shizzn

3
##### Support / Vuforia Rotation Matrix to jPCT Rotation Matrix
« on: August 27, 2013, 12:10:21 pm »
Hallo and howdy,

I successfully integrated Vuforia into my jPCT-AE project and instead of changing the camera Position I change the position of the 3D-Objects in relation to the camera.
Therefore I use the pose matrix of the Vuforia SDK which is a 3x4 matrix:
poseMatrix = [R|t]
R is the 3x3 rotation matrix
t is the 1x3 translation matrix

I track several markers and put one 3D-Object on each of them. To set the position of the marker I use the translation matrix. This works like a charm.

But I have problems setting the rotation of the objects. I use the setRotationMatrix method of the Object3D class.
Therefore I first hardcode my Vuforia 3x3 rotation matrix in a 4x4 jPCT rotation matrix like described in this jPCT-Thread.
This works. But the coordinate system of jPCT is rotated 180 degrees around the x axis with respect to Vuforia's coordinate system.
That's why the 3D-Objects just rotate in the wrong direction. With transposing Vuforia's 3x3 rotation matrix I get the right rotation but the objects seem to be behind the marker. This is pretty ugly.
I could just move the objects in front of the marker but this is not the way I want to solve this problem, because I have several (probably) different sized objects.

My Question: Can Vuforia's rotation matrix be changed (rotated) to a jPCT's rotation matrix with respect to their different coordination systems?

Greetings
Shizzn

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