请教这句代码是什么意思？
红色的这句：
struct feature
{
double x; /**< x coord */
double y; /**< y coord */
double a; /**< Oxford-type affine region parameter */
double b; /**< Oxford-type affine region parameter */
double c; /**< Oxford-type affine region parameter */
double scl; /**< scale of a Lowe-style feature */
double ori; /**< orientation of a Lowe-style feature */
int d; /**< descriptor length */
double descr[FEATURE_MAX_D]; /**< descriptor */
int type; /**< feature type, OXFD or LOWE */
int class; /**< all-purpose feature class */
struct feature* fwd_match; /**< matching feature from forward image */
struct feature* bck_match; /**< matching feature from backmward image */
struct feature* mdl_match; /**< matching feature from model */
CvPoint2D64f img_pt; /**< location in image */
CvPoint2D64f mdl_pt; /**< location in model */
void* feature_data; /**< user-definable data */
};
