Scan Pattern

The scan pattern defines the movement of the mirrors. The key parameters of the pattern are the horizontal and vertical fields of view (FoV) as well as the number of scan lines per frame. The frame rate is defined by the total number of scan lines and the oscillation frequency of the mirrors which is fixed and device-specific.

Table 1. Available fields in blickfeld.system.config.ScanPattern
Field	Type	Default	Unit
horizontal	Horizontal	-	-
vertical	Vertical	-	-
pulse	Pulse	-	-
read_only	bool	false	-
read_only	this is an read_only flag and it will be set if this is a default scan pattern, which can’t be changed or deleted.
frame_rate	optional FrameRate	-	-
frame_mode	FrameMode	FRAME_MODE_UP_DOWN	-

Horizontal

This section defines the movement of the horizontal mirror. The mirror moves continuously with its own frequency. Each half-oscillation period of the mirror results in one scan line.

Table 2. Available fields in blickfeld.system.config.ScanPattern.Horizontal
Field	Type	Default	Unit
field_of_view	float	1.57079637	rad
field_of_view	Unit: [rad] – optical field of view of the horizontal mirror. Note: In v2.2* and below, this was defined as a mechanical FoV.

Vertical

This section defines the movement of the vertical mirror within one frame. The mirror moves for from 0 degrees to the configured target FoV (up-ramping phase) and back to 0 degrees (down-ramping phase) with its eigenfrequency. The number of scanlines for each phase can be configured. Due to the dynamics of the mirror, a certain number of scan lines are required to reach the target FoV and then to reach 0 degrees again. Consequently, if the limit is reached, a lower number of scan lines requires a reduced FoV. Thus, a higher number of scan lines allows a larger vertical FoV. The vertical FoV is limited by the optical components.

Note: Due to the time required for one scan line, the rounded even number of scan lines directly scales inverse proportionally with the frame rate.

Table 3. Available fields in blickfeld.system.config.ScanPattern.Vertical
Field	Type	Default	Unit
field_of_view	float	0.87266463	rad
field_of_view	Unit: [rad] – FoV in the center of the frame. Due to the eye shape of the scan pattern, the vertical FoV decreases the outer boundaries of the horizontal mirror.
scanlines_up	optional uint32	40	-
scanlines_up	Configures the number of scan lines required for the up-ramping phase. During the up-ramping phase, the vertical mirror increases its amplitude from 0 degrees to the target FoV. Default: 200
scanlines_down	optional uint32	40	-
scanlines_down	Configures the amount of scan lines required for the down-ramping phase. During the down-ramping phase, the vertical mirror decreases its amplitude from the target FoV to 0 degrees. Default: 30
foveation	optional Foveation	-	-
foveation	Optionally configures a foveated region.

Foveation

Configures a vertical field of view foveation.

This enables the user to specify a region of interest with a different scanline density which is defined as the number of scanlines per degree of vertical field of view. For constant frame rate this allows increasing the resolution in the region of interest without having to reduce the vertical field of view.

Table 4. Available fields in blickfeld.system.config.ScanPattern.Vertical.Foveation
Field	Type	Default	Unit
fraction	float	0.2	-
fraction	The fraction of the field of view that the density factor is applies to. The allowed value range is [0.15, 0.85].
density_factor	float	3	-
density_factor	The foveation density factor defines the ratio of scanline density and consequently point density inside the foveated region compared to outside of it.
scanlines	optional uint32	-	-
scanlines	Read-only parameter showing the number of scanlines in the foveated region. If the frame mode is set to up-down or separate, this applies to both the up-ramping and down-ramping phase individually.

Pulse

This section defines the pattern in which the laser pulses and captures sample points

Table 5. Available fields in blickfeld.system.config.ScanPattern.Pulse
Field	Type	Default	Unit
angle_spacing	optional float	0.0043633231	rad
angle_spacing	Unit: [rad] – This defines the angle within which the horizontal mirror moves between two laser pulses. This parameter therefore defines the horizontal sampling resolution.
uniform	optional Uniform	-	-
uniform	Optional configure a uniform scan pattern

Uniform

Configure the uniform scan pattern

The classic scan pattern does not benefit uniformly from increasing the scanline count in a frame. The uniform scan pattern is an optimization that tries to provide an optimally homogeneous point cloud given the system’s constraints. To configure the scan pattern, the vertical field of view, the target frame rate and the pulse mode are used.

Table 6. Available fields in blickfeld.system.config.ScanPattern.Pulse.Uniform
Field	Type	Default	Unit
pulse_mode	eye_safety.data.PulseMode	PULSE_MODE_B	-
pulse_mode	Pulse mode to use for the uniform scan pattern. This will overwrite the horizontal angle spacing.

Frame Rate

This section defines the frame rate of a scan pattern

Table 7. Available fields in blickfeld.system.config.ScanPattern.FrameRate
Field	Type	Default	Unit
target	optional double	-	Hz
target	Target frame rate used to synchronize the point clouds of multiple LiDAR devices in a sensor setup
actual	optional double	-	Hz
actual	Read-only parameter for the actual frame rate the LiDAR is currently running at
maximum	optional double	-	Hz
maximum	IMPORTANT: This field is deprecated. It has been replaced by "actual" and will not be supported in future releases. Read-only parameter for maximum achievable frame rate of the scan pattern

Frame Mode

The frame mode specifies the point cloud frame’s composition and can be used to fine tune the LiDAR to specific use cases.

Table 8. Available values for blickfeld.system.config.ScanPattern.FrameMode enum
Name	Value	Description
FRAME_MODE_UNSPECIFIED	0	Unspecified frame mode
FRAME_MODE_UP_DOWN	1	The laser will trigger both during up and downramping phase and a point cloud frame is the combination of the two. Points that are close in azimuth and elevation in both phases will be recorded up to two seconds apart, this mode is therefore recommended only for high frame rates or scenes without fast objects.
FRAME_MODE_UP	2	The laser will only trigger during the upramping phase. Because no laser is fired during the downramping phase, this mode results in a more uniform motion deformation for fast objects.
FRAME_MODE_SEPARATE	3	The laser will trigger both during up and downramping phase but separate point cloud frames will be emitted, which maximizes frame rate.

Named Scan Pattern

Temporary container used for config storage TODO Remove when map type is supported.

Table 9. Available fields in blickfeld.system.config.NamedScanPattern
Field	Type	Default	Unit
name	optional string	-	-
scan_pattern	ScanPattern	-	-