The SpriteNode positions a Sprite in a 3D scene. Sprites are positioned in world space, but rendered in screen space. That means, the position of the scene node is projected into the current viewport and the 2D sprite is rendered at the resulting pixel position. The orientation of the scene node is irrelevant, it has no influence on how the sprite is rendered.

Hit Testing:
The properties LastBounds, LastDepth, and LastFrame can be used for simple hit testing, i.e. to check whether a pixel position hits the sprite. Hit testing against LastBounds and LastDepth has the following limitations:

• No occlusion: It is not possible to check whether the sprite was occluded by other objects. Hit testing against the LastBounds may return a hit even when the sprite is occluded by other geometry.
• No rotations: The property LastBounds stores the unrotated bounding box. I.e. hit testing against rotated sprites does not work.
• No transparency: Transparent parts of the sprite count as a hit.

The following method can be used to make a hit test against the sprite node:

// Test whether a mouse position hits the sprite.
public static bool HitTest(IGraphicsService graphicsService, SpriteNode node, Point p)
{
  // Disabled nodes can be ignored.
  if (!node.IsEnabled)
    return false;

  // node.LastBounds is only valid if the sprite node was rendered in the last frame.
  if (node.LastFrame != graphicsService.Frame)
    return false;

  return node.LastBounds.Contains(p);
}

If multiple sprite nodes are hit, the property LastDepth can be used to sort the resulting sprite nodes by distance to the viewer.

Reference