Scan cutting

This page details the design of the scan cutting logic for sensors with per-channel angle correction.

Supported Sensors

Precise scan cutting is currently supported for the following vendors:

See the Hesai configuration page for how to configure this feature.

Problem Statement

Some sensor models, such as most Hesai sensors, have per-channel azimuth offset terms that result from the channels' different firing times. This results in a given block with a given encoder azimuth to have a range of point azimuths. This spread needs to be taken into account when cutting and publishing scan frames.

In particular, in the region around the configured cut angle, two scan frames are overlapping due to this spread, and points from one packet are split between the two frames. The timing of when to initialize the next frame (e.g. set its timestamp) and when to emit the current frame (e.g. publish it) needs to be carefully defined.

Additionally, around field of view (FoV) boundaries, a subset of channels may produce points inside the FoV, while others produce points outside the FoV.

Assumptions

• There can be packet loss, but consecutive lost packets span less than \(360^\circ - 2 \cdot spread\) where spread is the maximum difference between the azimuths of any two channels in a block.
• There is at least one packet after all channels have crossed out of the FoV.

Cases that are violating the above assumptions are marked with ⛔ in the below tables and diagrams.

Action Definitions

Cutting in FoV

State definitions:

Analogously for F1 and C1->0.

Transition actions:

Analogously for F1 and C1->0.

Cutting at FoV End

State definitions:

Analogously for O1, F1, and C1->0.

Transition actions:

Analogously for O1, F1, and C1->0.