some confusions about Bbox label definition

[Dongzhou-1996]

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]

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]

@halostorm
你好，请问 theta角是顺时针为正吗

[halostorm]

右手坐标系，逆时针

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------------------ 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 — Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications on the go with GitHub Mobile for iOS or Android. You are receiving this because you were mentioned.Message ID: ***@***.***>