Smac Hybrid-A* Planner¶
<name> is the corresponding planner plugin ID selected for this type.
Parameters¶
<name>.downsample_costmapType
Default
bool
False
- Description
Whether to downsample costmap to another resolution for search.
<name>.downsampling_factorType
Default
int
1
- Description
Multiplier factor to downsample costmap by (e.g. if 5cm costmap at 2
downsample_factor, 10cm output).
<name>.allow_unknownType
Default
bool
True
- Description
Whether to allow traversing/search in unknown space.
<name>.toleranceType
Default
double
0.25
- Description
If an exact path cannot be found, the tolerance (as measured by the heuristic cost-to-goal) that would be acceptable to diverge from the requested pose.
<name>.max_iterationsType
Default
int
1000000
- Description
Maximum number of search iterations before failing to limit compute time, disabled by -1.
<name>.max_on_approach_iterationsType
Default
int
1000
- Description
Maximum number of iterations once a visited node is within the goal tolerances to continue to try to find an exact match before returning the best path solution within tolerances. Negative values convert to infinite.
<name>.max_planning_timeType
Default
double
5.0
- Description
Maximum planning time in seconds.
<name>.analytic_expansion_ratioType
Default
double
3.5
- Description
Planner will attempt to complete an analytic expansions in a frequency proportional to this value and the minimum heuristic.
<name>.analytic_expansion_max_lengthType
Default
double
3.0
- Description
If the length is too far, reject this expansion. This prevents shortcutting of search with its penalty functions far out from the goal itself (e.g. so we don’t reverse half-way across open maps or cut through high cost zones). This should never be smaller than 4-5x the minimum turning radius being used, or planning times will begin to spike.
<name>.motion_model_for_searchType
Default
string
“DUBIN”
- Description
Motion model enum string to search with. For Hybrid-A* node, default is “DUBIN”. Options for SE2 are DUBIN or REEDS_SHEPP.
<name>.angle_quantization_binsType
Default
int
72
- Description
Number of angular bins to use for SE2 search. This can be any even number, but a good baseline is 64 or 72 (for 5 degree increments).
<name>.minimum_turning_radiusType
Default
double
0.4
- Description
Minimum turning radius in meters of vehicle. Also used in the smoother to compute maximum curvature.
<name>.reverse_penaltyType
Default
double
2.0
- Description
Heuristic penalty to apply to SE2 node if searching in reverse direction. Only used in
REEDS_SHEPPmotion model.
<name>.change_penaltyType
Default
double
0.0
- Description
Heuristic penalty to apply to SE2 node if changing direction (e.g. left to right) in search. Disabled by default after change to guarantee admissibility of the Hybrid-A* planner.
<name>.non_straight_penaltyType
Default
double
1.20
- Description
Heuristic penalty to apply to SE2 node if searching in non-straight direction.
<name>.cost_penaltyType
Default
double
2.0
- Description
Heuristic penalty to apply to SE2 node for cost at pose. Allows Hybrid-A* to be cost aware.
<name>.retrospective_penaltyType
Default
double
0.015
- Description
Heuristic penalty to apply to SE2 node penalty. Causes Hybrid-A* to prefer later maneuvers before earlier ones along the path. Saves search time since earlier (shorter) branches are not expanded until it is necessary. Must be >= 0.0 and <= 1.0. Must be 0.0 to be fully admissible.
<name>.lookup_table_sizeType
Default
double
20.0
- Description
Size of the dubin/reeds-sheep distance window to cache, in meters.
<name>.viz_expansionsType
Default
bool
false
- Description
Whether to publish expansions on the
/expansionstopic as an array of poses (the orientation has no meaning). WARNING: heavy to compute and to display, for debug only as it degrades the performance.
<name>.cache_obstacle_heuristicType
Default
bool
false
- Description
Cache the obstacle map dynamic programming distance expansion heuristic between subsiquent replannings of the same goal location. Dramatically speeds up replanning performance (40x) if costmap is largely static.
<name>.smooth_pathType
Default
bool
true
- Description
If true, does simple and fast smoothing post-processing to the path from search
<name>.smoother.max_iterationsType
Default
int
1000
- Description
The maximum number of iterations the smoother has to smooth the path, to bound potential computation.
<name>.smoother.w_smoothType
Default
double
0.3
- Description
Weight for smoother to apply to smooth out the data points
<name>.smoother.w_dataType
Default
double
0.2
- Description
Weight for smoother to apply to retain original data information
<name>.smoother.toleranceType
Default
double
1e-10
- Description
Parameter tolerance change amount to terminate smoothing session
<name>.smoother.do_refinementType
Default
bool
true
- Description
Performs extra refinement smoothing runs. Essentially, this recursively calls the smoother using the output from the last smoothing cycle to further smooth the path for macro-trends. This typically improves quality especially in the Hybrid-A* planner due to the extra “wobbling” it can have due to the very small primitive lengths but may cause the path to get slightly closer to some obstacles.
<name>.smoother.refinement_numType
Default
int
2
- Description
Number of times to recursively attempt to smooth, must be
>= 1.
Example¶
planner_server:
ros__parameters:
planner_plugins: ["GridBased"]
use_sim_time: True
GridBased:
plugin: "nav2_smac_planner/SmacPlannerHybrid"
downsample_costmap: false # whether or not to downsample the map
downsampling_factor: 1 # multiplier for the resolution of the costmap layer (e.g. 2 on a 5cm costmap would be 10cm)
tolerance: 0.25 # dist-to-goal heuristic cost (distance) for valid tolerance endpoints if exact goal cannot be found.
allow_unknown: true # allow traveling in unknown space
max_iterations: 1000000 # maximum total iterations to search for before failing (in case unreachable), set to -1 to disable
max_on_approach_iterations: 1000 # Maximum number of iterations after within tolerances to continue to try to find exact solution
max_planning_time: 5.0 # max time in s for planner to plan, smooth
motion_model_for_search: "DUBIN" # Hybrid-A* Dubin, Redds-Shepp
angle_quantization_bins: 72 # Number of angle bins for search
analytic_expansion_ratio: 3.5 # The ratio to attempt analytic expansions during search for final approach.
analytic_expansion_max_length: 3.0 # For Hybrid/Lattice nodes: The maximum length of the analytic expansion to be considered valid to prevent unsafe shortcutting
minimum_turning_radius: 0.40 # minimum turning radius in m of path / vehicle
reverse_penalty: 2.0 # Penalty to apply if motion is reversing, must be => 1
change_penalty: 0.0 # Penalty to apply if motion is changing directions (L to R), must be >= 0
non_straight_penalty: 1.2 # Penalty to apply if motion is non-straight, must be => 1
cost_penalty: 2.0 # Penalty to apply to higher cost areas when adding into the obstacle map dynamic programming distance expansion heuristic. This drives the robot more towards the center of passages. A value between 1.3 - 3.5 is reasonable.
retrospective_penalty: 0.015
lookup_table_size: 20.0 # Size of the dubin/reeds-sheep distance window to cache, in meters.
cache_obstacle_heuristic: false # Cache the obstacle map dynamic programming distance expansion heuristic between subsiquent replannings of the same goal location. Dramatically speeds up replanning performance (40x) if costmap is largely static.
viz_expansions: false # For Hybrid nodes: Whether to publish expansions on the /expansions topic as an array of poses (the orientation has no meaning). WARNING: heavy to compute and to display, for debug only as it degrades the performance.
smooth_path: True # If true, does a simple and quick smoothing post-processing to the path
smoother:
max_iterations: 1000
w_smooth: 0.3
w_data: 0.2
tolerance: 1.0e-10
do_refinement: true
refinement_num: 2