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Since I haven’t seen this on Stackoverflow, the following is a method to transform a vector (GLKVector3) based on an attitude quaternion (GLKQuaternion).

First, assume that you have a GLKVector3 as input, call it inputVector3. inputVector3 could be yaw, pitch, and roll influences from an aircraft’s control surfaces or thruster output on a spacecraft. You know your vehicle’s attitude and have calculated that attitude into a quaternion. So, the goal is to have the inputVector3 transformed into an ivar, say GLKVector3 deltaV, that is in terms of the vehicle’s attitude.

– (GLKVector3)transformVector3:(GLKVector3)inputVector3 withAttitudeQuaternion:(GLKQuaternion)attitudeQuaternion
{
GLKVector3 deltaV = inputVector3;

//Always ensure that your attitude quaternion has been normalized
attitudeQuaternion = GLKQuaternionNormalize(attitudeQuaternion);

//Convert the normalized attitude quaternion into a GLKMatrix3.
GLKMatrix3 tempQMatrix3 = GLKMatrix3MakeWithQuaternion(attitudeQuaternion);

//Since v’ = v T, where T is a transform matrix, multiply
//the attitudeQuaternion GLKMatrix3 with the necessary GLKVector3.
deltaV = GLKMatrix3MultiplyVector3(tempQM3, deltaV);

return deltaV;
}

When: February 28, 7:00 PM

Where: TechShop
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What:
From 7:00 – 7:30, it’s Show-&-Tell. So bring your code and your apps and show them off.

Carl Brown will give us a tour of an example open-source (MIT license) app he wrote to illustrate using a REST (web) API with JSON and Core Data. The source code is at http://github.com/car… if you want to follow along.

When: February 21, 7:00 PM

Where: TechShop
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What:
From 7:00 – 7:30, it’s Show-&-Tell. So bring your code and your apps and show them off.

This will be GLKit Night. GLKit is Apple’s way of making OpenGL ES more approachable and easier to use for developers. And what’s not to like about GLKit or -snapshot?

Rajat will talk about GLKit and shaders. While GLKit tries to shade one from having to write Shaders, sometimes you just have to shade. For example, let’s say you want shadows? After Rajat finishes, you’ll be have a better understanding of both GLKit, shaders, and how they can work together.

Jim will talk about his experience with GLKit in building his ISS Space Station app. There isn’t a lot of sample code on how to use GLKBaseEffect, GLKMatrixStack, and even how to build a nice spotlight, so his presentation will hopefully help those wondering how to shove your GLKBaseEffect instance into GLKMatrixStack.