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halostorm / PCAT_open_source

PointCloud Annotation Tools, support to label object bound box, ground, lane and kerb
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some confusions about Bbox label definition #8

Closed Dongzhou-1996 closed 4 years ago

Dongzhou-1996 commented 4 years ago

image According to the definition of bbox label u provided in 'image/s5.png', the object of interest can be described by its size (length, width, height), location (x_c, y_c, z_c), theta and alpha. However, I have three question about the definition of bbox label:

  1. which object point does the location (x_c, y_c, z_c) represents? the center of target or just like KITTI dataset (the bottom center of target)? And is the location (x_c, y_c, z_c) the original of object coordinate system?

  2. the 3D size of object includes length, width and height, Which axis of object coordinate system are they respectively aligned with? length-x, width-y, height-z?

  3. how is the alpha defined? the angle between the x-axis of observer coordinates and the x-axis of object coordinates? which case is it defined as positive？and when is negative?

regards, dong zhou

根据你们在 'image/s5.png' 所提供的bbox label定义来看，感兴趣目标能够由 size (length, width, height), location (x_c, y_c, z_c), theta and alpha 来描述。 但是我对bbox label定义有几个问题没有弄明白：

  1. label中的the location (x_c, y_c, z_c) 对应目标的哪个点？目标中心或者像KITTI数据集那样，对应目标底面中心？还有the location (x_c, y_c, z_c) 应该就是目标坐标系的原点吧？

  2. 目标三维尺寸包括长、宽、高，它们分别对应目标坐标系的哪个轴？长对应x轴，宽对应y轴，高对应z轴？

  3. alpha角是如何定义的？它是观测坐标系x轴和目标坐标系x轴的夹角吗？这个alpha角什么时候为正，什么时候为负？

非常期待您的回答！ 周栋

halostorm commented 4 years ago
  1. label中的the location (x_c, y_c, z_c) 对应目标的哪个点？目标中心或者像KITTI数据集那样，对应目标底面中心？还有the location (x_c, y_c, z_c) 应该就是目标坐标系的原点吧？ 参考系是采集车车体系，(x_c, y_c, z_c) 是3Dbbox中心
  2. 目标三维尺寸包括长、宽、高，它们分别对应目标坐标系的哪个轴？长对应x轴，宽对应y轴，高对应z轴？ 对的。
  3. alpha角是如何定义的？它是观测坐标系x轴和目标坐标系x轴的夹角吗？这个alpha角什么时候为正，什么时候为负？ x轴夹角，符号定义，正->逆时针
russellyq commented 2 years ago

@halostorm 你好，请问 theta角是顺时针为正吗

halostorm commented 2 years ago

右手坐标系，逆时针

------------------ Original ------------------ From: russellyq @.> Date: Tue,Jan 18,2022 2:13 PM To: halostorm/PCAT_open_source @.> Cc: halo @.>, Mention @.> Subject: Re: [halostorm/PCAT_open_source] some confusions about Bbox labeldefinition (#8)

@halostorm 你好，请问 theta角是顺时针为正吗

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