nav_grid_pub_sub

The nav_2d_msgs package provides two message types for publishing / receiving the data for an entire nav_grid::NavGrid.

• nav_2d_msgs::NavGridOfChars for nav_grid::NavGrid<unsigned char> and
• nav_2d_msgs::NavGridOfDoubles for nav_grid::NavGrid<double>

There are also two message types for publishing a rectangular sub-portion of the NavGrid.

• nav_2d_msgs::NavGridOfCharsUpdate
• nav_2d_msgs::NavGridOfDoublesUpdate

These messages are analagous to nav_msgs::OccupancyGrid and map_msgs::OccupancyGridUpdate. However, OccupancyGrid does not support floating point and its char values are scaled to [0, 100]. This class also provides support for publishing / receiving OccupancyGrid and OccupancyGridUpdate messages, but the data needs to be scaled, which is discussed here.

This package provides mechanisms for publishing and receiving both the whole grid message and the update message in a unified manner.

Publishing

The publisher requires a nav_grid::NavGrid& at construction, and is initialized with a NodeHandle.

By default, it will create publishers for

• NavGridOfX messages (depending on the datatype of the NavGrid)
• OccupancyGrid messages
• The two related Update messages
• A PolygonStamped message for visualizing the update area.

You can rename the topics these message are published on by passing different strings into the initialize method, or turn the publishing for certain messages off entirely by passing in the empty string.

The whole grid is published by calling publish() using data from the NavGrid. An update is published with publish(bounds).

You can also limit how often the full OccupancyGrid/NavGridOfChars message is published with the full_publish_cycle parameter.

• If the full_publish_cycle is 0, which is the default, the full grid will be published every time you call publish.
• If the full_publish_cycle is negative, you avoid publishing all together.
• Otherwise, the full grid will only be published when publish is called if full_publish_cycle time has passed since the last full grid publish.
• Note that full grids may also be published when attempting to publish an update but the grid info has changed

You can control how often updates are published with similar logic and the update_publish_cycle argument. If the

• update_publish_cycle is positive, the Bounds from successive calls will be merged so the resulting update will
• cover the superset of all the bounds.

Subscribing

The subscribers also require a nav_grid::NavGrid& at construction.

However, each will only subscribe to OccupancyGrid OR NavGridOfX (and their updates), not both.

• The standard way to subscribe to OccupancyGrid messages is with nav_grid_pub_sub::NavGridSubscriber initialized with nav_grid=False which will write into a nav_grid::NavGrid<unsigned char>. You could also theoretically use nav_grid_pub_sub::NavGridOfDoublesSubscriber to write to nav_grid::NavGrid<double>, but you would likely need to set your own interpretation function for that.
• On the other hand, if you set nav_grid=True it will subscribe to NavGridofChars or NavGridOfDoubles depending on if you use nav_grid_pub_sub::NavGridSubscriber or nav_grid_pub_sub::NavGridOfDoublesSubscriber.

The data is automatically applied to the NavGrid, and new data will trigger a callback function that is passed in as a parameter so that other classes can be notified of how much of the costmap has changed.