====== envelop point Y coordinate trees ======
These trees are built as [[canonical huffman trees]]. Remember that negative values are 2's complement encoded and thus appear after the positive values in the trees.

===== delta x for decreasing y tree ======
  * 0: not possible
  * 1: 2 bits
  * 2, 3: 3 bits
  * 4..7: 4 bits
  * 8..11: 5 bits
  * 12..15: 6 bits
  * 16..31: 8 bits

===== delta x for increasing y tree ======
  * 0: not possible
  * 1: 4 bits
  * 2..6: 3 bits
  * 7, 8: 4 bits
  * 9, 10: 5 bits
  * 11..13: 6 bits
  * 14, 15: 7 bits
  * 16..31: 8 bits

===== delta x to master tree =====
  * -16..-4: 7 bits
  * -3, -2: 6 bits
  * -1: 4 bits
  * 0: 1 bit
  * 1, 2: 4 bits
  * 3, 4: 5 bits
  * 5..8: 6 bits
  * 9..15: 7 bits

===== delta x to previous band for decreasing y tree ======
  * -16..-7: 6 bits
  * -2..-6: 5 bits
  * -1: 4 bits
  * 0: 2 bits
  * 1: 4 bits
  * 2..7: 5 bits
  * 8..15: 6 bits

===== delta x to previous band for increasing y tree ======
  * -16..-5: 5 bits
  * -4..-3: 4 bits
  * -2..-1: 5 bits
  * 0: 4 bits
  * 1..4: 5 bits
  * 5..10: 6 bits
  * 11..15: 5 bits