Minecraft:Heightmap

Heightmaps are maps to store the Y-level of the highest block at each horizontal coordinate. They are stored in chunk files and used for various game calculations.

Motion blocking

The last four heightmaps are based on a property called motion blocking. This is defined as follows:

• Minecraft:Cobwebs and Minecraft:bamboo saplings are considered not motion blocking.
• The block must be "solid". On Template:JE, this is defined using the Minecraft:Legacy solid property. Note that this is not the same as having a collision box. Some blocks like snow Minecraft:azaleas are not considered solid while having a collision box, and other blocks like Minecraft:banners are considered solid while having no collision box.

Types

Several different heightmaps check and store highest block of different types, and are used for different purposes. Template:IN, there are six heightmap types:

• WORLD_SURFACE: Stores the Y-level of the highest non-air (all types of air) block.
• WORLD_SURFACE_WG: Stores the Y-level of the highest non-air (all types of air) block. Used only during world generation.
• OCEAN_FLOOR: Stores the Y-level of the highest block whose Minecraft:material blocks motion. Used only on the server side.
• OCEAN_FLOOR_WG: Stores the Y-level of the highest block whose material blocks motion. Used only during world generation.
• MOTION_BLOCKING: Stores the Y-level of the highest block whose material blocks motion or blocks that contains a fluid (Minecraft:water, Minecraft:lava, or Minecraft:waterlogged blocks).
• MOTION_BLOCKING_NO_LEAVES: Stores the Y-level of the highest block whose material blocks motion, or blocks that contains a fluid (water, lava, or waterlogged blocks), except various Minecraft:leaves. Used only on the server side, e.g. for pillager patrol spawning.

Usage

Heightmaps are used for various in-game calculations. For example, a lightning rod can only be triggered when there is no non-air block above it. Therefore, the game compares the Y-level of lightning rod with heightmap WORLD_SURFACE to know if there are non-air blocks above it.

Heightmaps of both server side and client side can be seen in Minecraft:debug screen. The "CH" line is the value in client side heightmaps at the player's current X/Z coordinates. The "SH" line is the server side value in heightmaps at the player's current X/Z coordinates. In the two lines:

• S means WORLD_SURFACE
• O means OCEAN_FLOOR
• M means MOTION_BLOCKING
• ML means MOTION_BLOCKING_NO_LEAVES

Template:Cmd can change the execution position of the command to one block above the Y-level stored in the specified heightmap. WORLD_SURFACE_WG and OCEAN_FLOOR_WG cannot be used in this command.