[Question] Extracting the heights of the surface of the ground terrain

[sashenkalex]

Question

Hello,

I’m working on a locomotion training task in IsaacLab. I’m currently setting up related rewards, and I’d like to get the height of the feet like this relative to the terrains like stairs and slopes. To do so, I'm just wondering whether we can extract the height value of the terrain surface. Are there any functions for this in IsaacLab?

[PeterL-NV]

To extract the height value of a terrain surface in IsaacLab, access to the height field array is required, as terrains are typically represented by 2D numpy arrays where each cell denotes the surface height at a specific (x, y) coordinate. For height field terrains, IsaacLab provides or generates this array during terrain creation, and sampling it can be achieved by mapping world (x, y) positions to height field grid indices.

How to Extract Terrain Height

• When generating a height field terrain using IsaacLab's terrain generator utilities (such as those under isaaclab.terrains.height_field.hf_terrains), the terrain height data is returned as a 2D numpy array, with discretization determined by the configuration (e.g., horizontal_scale, vertical_scale).
• By knowing the origin, step sizes (scales), and querying (x, y) position, the corresponding height is:

# Given a height field 'hf' as a (width, length) numpy array
# and horizontal/vertical scales (in meters):
horizontal_scale = cfg.horizontal_scale
vertical_scale = cfg.vertical_scale

# World coordinates (x, y)
x_world = ...
y_world = ...

# Convert to index in the numpy array
i = int(x_world / horizontal_scale)
j = int(y_world / horizontal_scale)

# Clip to array bounds to avoid index errors
i = np.clip(i, 0, hf.shape[^0] - 1)
j = np.clip(j, 0, hf.shape[^1] - 1)

# Get height (in height field units, multiply by vertical_scale if needed)
height = hf[i, j] * vertical_scale

• This method can be adapted for any custom terrain as long as the height field and metadata are available.

[sashenkalex]

Hi, thank you for your reply.
Then, how can I access to that hf when I'm defining the reward function?