How to correctly accelerate a rotated 3d model in XNA? - xna-4.0

Question

How do I manipulate the matricies to keep my ship's velocity in the direction that the acceleration applies?
The current code doesn't work in that when I apply acceleration and then apply rotation, the acceleration changed with it.
I'm looking for the effect of a space ship as opposed to an airplane here.
Any help is appreciated - I know this is elementary stuff for you game programmers!
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using System;
namespace AsteroidsWindowsGAme
{
public class ShipModel
{
Model model;
Matrix[] boneTransforms;
ModelBone shipModelBone;
Matrix shipTransform;
TimeSpan lastTime;
public void Load(ContentManager content)
{
model = content.Load<Model>("Ship");
shipModelBone = model.Bones["Ship"];
shipTransform = shipModelBone.Transform;
boneTransforms = new Matrix[model.Bones.Count];
}
public void UpdateVelocity(GameTime gameTime)
{
if (AccelerationX != 0 || AccelerationY != 0 || AccelerationZ != 0)
{
if (lastTime == null)
{
lastTime = gameTime.TotalGameTime;
}
else
{
TimeSpan elapsedTime = gameTime.TotalGameTime - lastTime;
float elapsedSeconds = (float)elapsedTime.TotalSeconds;
VelocityX += AccelerationX * elapsedSeconds;
VelocityY += AccelerationY * elapsedSeconds;
VelocityZ += AccelerationZ * elapsedSeconds;
}
}
}
public void UpdatePosition(GameTime gameTime)
{
if(VelocityX != 0 || VelocityY != 0 || VelocityZ != 0)
{
if (lastTime == null)
{
lastTime = gameTime.TotalGameTime;
}
else
{
TimeSpan elapsedTime = gameTime.TotalGameTime - lastTime;
float elapsedSeconds = (float)elapsedTime.TotalSeconds;
PositionX += VelocityX * elapsedSeconds;
PositionY += VelocityY * elapsedSeconds;
PositionZ += VelocityZ * elapsedSeconds;
}
}
}
public void Draw(Matrix world, Matrix view, Matrix projection)
{
model.Root.Transform = world;
Matrix shipRotationMatrix =
Matrix.CreateTranslation(PositionX, PositionY, PositionZ) *
Matrix.CreateRotationX(RotationX) *
Matrix.CreateRotationY(RotationY) *
Matrix.CreateRotationZ(RotationZ);
shipModelBone.Transform = shipTransform * shipRotationMatrix;
model.CopyAbsoluteBoneTransformsTo(boneTransforms);
foreach (ModelMesh mesh in model.Meshes)
{
foreach (BasicEffect effect in mesh.Effects)
{
effect.World = boneTransforms[mesh.ParentBone.Index];
effect.View = view;
effect.Projection = projection;
effect.EnableDefaultLighting();
}
mesh.Draw();
}
}
public float RotationX { get; set; }
public float RotationY { get; set; }
public float RotationZ { get; set; }
public float PositionX { get; set; }
public float PositionY { get; set; }
public float PositionZ { get; set; }
public float VelocityX { get; set; }
public float VelocityY { get; set; }
public float VelocityZ { get; set; }
public float AccelerationX { get; set; }
public float AccelerationY { get; set; }
public float AccelerationZ { get; set; }
}
}

Answer 1

I figured this out: the solution is to multiply the translation matrix by the view matrix like this:
public void Draw(Matrix world, Matrix view, Matrix projection)
{
model.Root.Transform = world;
Matrix shipRotationMatrix =
Matrix.CreateRotationX(RotationX) *
Matrix.CreateRotationY(RotationY) *
Matrix.CreateRotationZ(RotationZ);
shipModelBone.Transform = shipTransform * shipRotationMatrix;
model.CopyAbsoluteBoneTransformsTo(boneTransforms);
foreach (ModelMesh mesh in model.Meshes)
{
foreach (BasicEffect effect in mesh.Effects)
{
effect.World = boneTransforms[mesh.ParentBone.Index];
effect.View = view * Matrix.CreateTranslation(PositionX, PositionY, PositionZ);
effect.Projection = projection;
effect.EnableDefaultLighting();
}
mesh.Draw();
}
}