A.R.Drone Developer Guide - Abstract

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7.1.3 Augmented reality data stream
In the previously described NavData, there are informations about vision-detected tags. The
goal is to permit to the host to add some functionalities, like augmented reality features. The
principle is that the AR.Drone sends informations on recognized pre-defined tags, like type
and position.
Listing 7.2: Navdata option for vision detection
typedef struct _navdata_vision_detect_t {
uint16_t tag;
uint16_t size;
uint32_t nb_detected;
uint32_t type[4];
uint32_t xc[4];
uint32_t yc[4];
uint32_t width[4];
uint32_t height[4];
uint32_t dist[4];
} __attribute__ ((packed)) navdata_vision_detect_t;
The drone can detect up to four 2D-tags. The kind of detected tag, and which camera to use,
can be set by using the configuration parameter detect_type.
Let’s detail the values in this block :
• nb_detected: number of detected 2D-tags.
• type[i]: Type of the detected tag #i ; see the CAD_TYPE enumeration.
• xc[i], yc[i]: X and Y coordinates of detected 2D-tag #i inside the picture, with (0, 0) being
the top-left corner, and (1000, 1000) the right-bottom corner regardless the picture resolution
or the source camera.
• width[i], height[i]: Width and height of the detection bounding-box (2D-tag #i), when
applicable.
• dist[i]: Distance from camera to detected 2D-tag #i in centimeters, when applicable.