Skeleton-based dynamic branch erasure for green mark turns

[Copilot]

The green mark turning algorithm erased fixed rectangular regions (modified[0:erase_bottom, 0:line_cx]) regardless of where skeleton branches actually were. This replaces that with connected-component analysis on the skeleton to identify and erase only the actual unwanted branches.

Approach

• Junction zone: Defined dynamically from both the green mark bounding box and the approach line center (line_cx), so the disconnection region always covers the real intersection
• Branch classification: After zeroing the junction zone in the skeleton, cv2.connectedComponentsWithStats separates individual branches. Each is classified by its entry point direction relative to the mark center (approach/left/right/top)
• Selective erasure: Unwanted branch components are collected into a mask, dilated to cover full line width, and applied to the binary image. Junction zone pixels on the unwanted side are included in the mask
• Keep-mask protection: A keep mask is built from preserved skeleton branches (including approach line and desired-side junction zone pixels), dilated by the same radius, and subtracted from the erase mask to prevent dilation bleed into kept branches
• Line-width-based dilation: Instead of using the green mark width for dilation sizing, the actual binary line width is measured at the approach line and used with a small margin, preventing over-aggressive erasure
• Fallback: Reverts to rectangular erasure when no branches are found outside the junction zone

Signature change

# Before
def _apply_green_turn_to_binary(binary_image: np.ndarray) -> np.ndarray:

# After
def _apply_green_turn_to_binary(binary_image: np.ndarray, skeleton: np.ndarray) -> np.ndarray:

The skeleton was already computed immediately before the call site in Linetrace_Camera_Pre_callback, so this just threads it through.

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[rotarymars]

@copilot I'm not sure whether you are good at reading images, but look at this.

This is removing the black lines that its on too aggressively. Can you fix it?

[Copilot]

@copilot I'm not sure whether you are good at reading images, but look at this.
![1773303775 062_tracking](https://github.com/user-attachments/assets/e6b29099-6c90-4d31-b559-ebab0a094...

Fixed in 891f722 and 65bdfd0. The over-aggressive erasure was caused by two issues:

1. Dilation radius was based on mark width (max(mark_w // 2, 15)) instead of actual line width — now it measures the real binary line width at the approach line and uses that + 3px margin (min 8px), which is much smaller.
2. No protection for kept branches — the dilated erase mask could bleed into the approach line and desired turn branch. Now a keep_mask is built from the kept skeleton branches (including approach line and desired-side junction zone pixels), dilated by the same radius, and subtracted from the erase mask before applying.

In tests, the approach line now retains 100% of its width near the junction (was being thinned from 16px to 1px before).

Warning

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