OS3D_POINT_SET

ID: 3104

Payload Definition

Data Type	Name	Description
u32	ping_number	assigned sequentially from power on
float	sos_mps	speed of sound (meters per second) used in angle calculations
u16	num_points	number of points reported in the points field
u16	unused	0
u32	unused	0
u64	utc_msec	time at start of ping, UTC milliseconds (1970 epoch). Will be 0 if not available.
u32	pwr up msec	time at start of ping from power on
u8	version	1. There was a previous version (0), see note below
u8	device number	must be < number of devices (so it will be 0 for a single device)
u8	unused	0
u8	reserved	0
float	pwr_threshold_high	Points with pwr higher than this are quite strong. This was the level used in all version 0 point sets. Seemed to be overly conservative.
float	pwr_threshold_med	This is a reasonable cutoff level for most applications.
float	pwr_threshold_low	This is a more liberal power level. If point_data is filtered with this threshold
u32	reserved[9]	reserved for future (9 words)
atof_t	point_data[num_points]	see below for atof_t definition

Notes

version: This is Version 1 of this packet format. Earlier there was a Version 0, which was applicable in some earlier beta units. These earlier files can be handled by SonarView and can be converted in SonarView as long as channel data was recorded.

power thresholds: The set of detected points is generously populated in the sense that some of these points are stronger than others and some may not be helpful. Three power thresholds are provided with which the points can be filtered if a more conservative selection of point detections is desired.

struct atof_point_t
{
	float angle; // radians;
	float tof;	 // time of flight in seconds
	float pwr;	 // power level of the beam at this point
	u8 pt_type;	 // 0 = unclassified, 1 = bottom_points, 2 = water column points
	u8 reserved[3] = {0,0,0};
} PACKED_STRUCT;

pt_type: At the time of this writing, all points emitted by the device will be of type "unclassified." In the future, we may implement further classification within the device.

Interpreting Angle

Zero angle is perpendicular to the face of the RX16 receive module. With the "dot" end of the RX16 facing the forward direction, and the transducer side down, positive angles are to the starboard side.

Note that the angles given in the data were computed with the speed of sound also given in the data. To adjust the angle in post processing for a different speed of sound, use the Snell's Law relation.

sin(angle1) / sos1 = sin(angle2) / sos2