读取PLY格式文件文件头加上元素数据列表。其中文件头中以行为单位描述文件类型、格式与版本、元素类型、元素的属性等，然后就根据在文件头中所列出元素类型的顺序及其属性，依次记录各个元素的属性数据。-PLY format file to read the file header plus the element data lists. Where the file header in units descr iption file type, format and version, the element type, element attributes, etc., and then based on the file header element types listed in the order of their properties, each element in turn record attribute data.