nih

// In QuadTreeComponent.QuadTree:

    public float GetTerrainDisplacement(Vector3 position)
        {
            //Debug.WriteLine("GetTerrainDisplacement1");
            return m_root.GetTerrainDisplacement(position.X, position.Z);
        }


// In QuadTreeComponent.QuadTreeNode:

        public float GetTerrainDisplacement(float x, float y)
        {
            if (x < m_startX || x >= m_endX)
                return OutOfRange;
            if (y < m_startY || y >= m_endY)
                return OutOfRange;

            if (m_heightData == null)
            {
                for (int i = 0; i < 4; i++)
                {
                    float ret;
                    if (child[i] != null)
                    {
                        ret = child[i].GetTerrainDisplacement(x, y);
                        if (ret != OutOfRange)
                            return ret;
                    }
                }
                return OutOfRange;
            }

            float thisX = x - m_startX;
            float thisY = y - m_startY;
            int mapX = (int)Math.Floor(thisX / m_cellSize);
            int mapY = (int)Math.Floor(thisY / m_cellSize);

            if (mapX < 0 || mapX >= m_width)
                throw new Exception("QuadtreeNode:GetTerrainDisplacement(x,y) x out of range.");
            if (mapY < 0 || mapY >= m_height)
                throw new Exception("QuadtreeNode:GetTerrainDisplacement(x,y) y out of range.");

            // Create a vector for each corner of the cell we're in
            Vector3 v1 = new Vector3((mapX + 0) * m_cellSize, m_heightData[(mapY + 0), (mapX + 0)], (mapY + 0) * m_cellSize);
            Vector3 v2 = new Vector3((mapX + 1) * m_cellSize, m_heightData[(mapY + 0), (mapX + 1)], (mapY + 0) * m_cellSize);
            Vector3 v3 = new Vector3((mapX + 0) * m_cellSize, m_heightData[(mapY + 1), (mapX + 0)], (mapY + 1) * m_cellSize);
            Vector3 v4 = new Vector3((mapX + 1) * m_cellSize, m_heightData[(mapY + 1), (mapX + 1)], (mapY + 1) * m_cellSize);

            // Get the relative position of where we are in the cell
            Vector3 rel = new Vector3(thisX, 0f, thisY) - v1;
            rel /= m_cellSize;

            // Linear interpolation time!
            // First, do the top edge (X axis)
            Vector3 L1 = Vector3.Lerp(v1, v2, rel.X);
            // Then the parallel bottom edge (Also x axis)
            Vector3 L2 = Vector3.Lerp(v3, v4, rel.X);
            // Then the Z axis which joins the two
            Vector3 L3 = Vector3.Lerp(L1, L2, rel.Z);

            // We have our height!
            float height = L3.Y;
            return height;
        }