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# Crosswalk Annotation Case Study

In the early 20 century, the British people designed a kind of horizontal crossing on the street. When pedestrians cross the street, they can only walk on the crossing. Therefore, there appeared a series of eye-catching lines in the streets of the city, which looked like the white stripes on the zebra body, so people called it zebra crossing. When a driver sees these white lines, he or she will consciously slow down or stop, to let pedestrians pass safely.

But how can assisted driving or autonomous driving recognize these stationary objects?

For example, when a child crosses the road for the first time, his parents will tell him what is a traffic light and what is a zebra crossing. This is the basic data processing that must be done before the automatic driving algorithm.

The annotated image serves as a realistic reference, telling the automated driving algorithm what is a traffic light and what is a zebra crossing. Through learning millions of images, the automatic driving algorithm keeps in-depth learning and correcting itself.

Let’s look at a case of crosswalk annotation.

1 Project Description

Label the visible crosswalk with 2D bounding box

2 Crosswalk Category

The crosswalk is divided into crosswalk and vertical crosswalk

(1) Crosswalk

(2) Vertical Crosswalk

3 Crosswalk Classification

There are three principles ranking from high to low:

(1) When there is only one crosswalk in the field of view: it should be labeled as a crosswalk.

(2) The crosswalk parallel to the lane of the vehicle is a crosswalk, and the one in vertical to the current lane is a vertical crosswalk.

(3) When the vehicle is turning at the intersection, according to the intersection angle of the crosswalk lines and the horizontal axis of the image, it is a vertical crosswalk when the angle is less than 45 degrees and a crosswalk when that is over 45 degrees.

4 Labeling Requirements

(1) The crosswalk should be divided into crosswalk and vertical crosswalk. And all the crosswalks in accordance with the labeling condition shall be labeled.

(2) All the crosswalks with the shortest side with more than 10 pixels.

(3) The bounding box should match the outline of the target. And the occluded part should be marked as well.

5 Special Scenarios

Annotation When Part of the Crosswalk Is Occluded

(1) One endpoint of the crosswalk is occluded: do not label the occluded object.

(2) The middle is occluded: label the occluded object with imagination.

Annotation When the Crosswalk Is Blurred

(1) For the wear and tear caused by vehicle running, imagine and label the complete area.

(2) Old crosswalk traces should be labeled.

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