/** \brief Various PCD file versions. * * PCD_V6 represents PCD files with version 0.6, which contain the following fields: * - lines beginning with # are treated as comments * - FIELDS ... * - SIZE ... * - TYPE ... * - COUNT ... * - WIDTH ... * - HEIGHT ... * - POINTS ... * - DATA ascii/binary * * Everything that follows \b DATA is interpreted as data points and * will be read accordingly. * * PCD_V7 represents PCD files with version 0.7 and has an important * addon: it adds sensor origin/orientation (aka viewpoint) information * to a dataset through the use of a new header field: * - VIEWPOINT tx ty tz qw qx qy qz */

这段代码是对PCD文件版本的说明文档。PCD_V6表示版本为0.6的PCD文件，它包含以下字段：
- 以#开头的行被视为注释
- FIELDS ...
- SIZE ...
- TYPE ...
- COUNT ...
- WIDTH ...
- HEIGHT ...
- POINTS ...
- DATA ascii/binary

在 \b DATA 之后的所有内容都会被解释为数据点，并相应地读取。

PCD_V7表示版本为0.7的PCD文件，并且增加了一个重要的附加信息：通过使用新的头字段，将传感器的起始位置/方向（也称为视点）信息添加到数据集中：
- VIEWPOINT tx ty tz qw qx qy qz