Message Filters

Agnocast provides message synchronization filters compatible with the ROS 2 message_filters API. These allow you to synchronize messages from multiple Agnocast topics based on their timestamps.

agnocast::message_filters::MessageEvent<M>

Wrapper around a message pointer that carries metadata for message filter pipelines.

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MessageEvent()

message_filters::MessageEvent<M>::MessageEvent()

Default-construct an empty MessageEvent.

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MessageEvent() [overload 2]

message_filters::MessageEvent<M>::MessageEvent(MessageEvent &rhs)

Copy constructor.

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MessageEvent() [overload 3]

message_filters::MessageEvent<M>::MessageEvent(ConstMessagePtr &message)

Construct from a message pointer, recording the current time as receipt time.

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MessageEvent() [overload 4]

message_filters::MessageEvent<M>::MessageEvent(ConstMessagePtr &message, rclcpp::Time receipt_time)

Construct from a message pointer and an explicit receipt time.

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operator=()

MessageEvent & message_filters::MessageEvent<M>::operator=(MessageEvent &rhs)

Copy assignment operator.

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getMessage()

ConstMessagePtr & message_filters::MessageEvent<M>::getMessage() const

Retrieve the message. Returns ipc_shared_ptr pointing to shared memory.

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getConstMessage()

ConstMessagePtr & message_filters::MessageEvent<M>::getConstMessage() const

Retrieve a const version of the message (same as getMessage() in agnocast)

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getReceiptTime()

rclcpp::Time message_filters::MessageEvent<M>::getReceiptTime() const

Returns the time at which this message was received.

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operator<()

bool message_filters::MessageEvent<M>::operator<(MessageEvent &rhs) const

Less-than comparison, ordered by pointer then receipt time.

agnocast::message_filters::SimpleFilter<M>

Extends: noncopyable

Base class for simple one-output filters. Provides callback registration and signal dispatch.

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registerCallback()

Connection message_filters::SimpleFilter<M>::registerCallback(C &callback)

Register a callback to be invoked when a message passes through this filter.

Parameter	Description
callback	Callback to register.
Returns	Connection object for disconnecting.

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setName()

void message_filters::SimpleFilter<M>::setName(std::string &name)

Set the name of this filter (for debugging).

Parameter	Description
name	Filter name.

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getName()

std::string & message_filters::SimpleFilter<M>::getName() const

Return the name of this filter.

Returns	Filter name string.

agnocast::message_filters::SubscriberBase<M>

Base class for Subscriber, allowing subscription management without knowing the message type. Used for type-erased subscriber collections.

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subscribe()

void message_filters::SubscriberBase<NodeType>::subscribe(NodePtr node, std::string &topic, rmw_qos_profile_t qos)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Default	Description
node	—	The rclcpp::Node::SharedPtr to use to subscribe.
topic	—	The topic to subscribe to.
qos	rmw_qos_profile_default	(optional) The rmw qos profile to use to subscribe.

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subscribe() [overload 2]

void message_filters::SubscriberBase<NodeType>::subscribe(NodeType *node, std::string &topic, rmw_qos_profile_t qos)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Default	Description
node	—	The rclcpp::Node to use to subscribe.
topic	—	The topic to subscribe to.
qos	rmw_qos_profile_default	(optional) The rmw qos profile to use to subscribe.

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subscribe() [overload 3]

void message_filters::SubscriberBase<NodeType>::subscribe(NodePtr node, std::string &topic, rmw_qos_profile_t qos, agnocast::SubscriptionOptions options)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe. This override allows SubscriptionOptions to be passed into the class without changing API.

Parameter	Description
node	The rclcpp::Node::SharedPtr to use to subscribe.
topic	The topic to subscribe to.
qos	The rmw qos profile to use to subscribe.
options	The subscription options to use to subscribe.

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subscribe() [overload 4]

void message_filters::SubscriberBase<NodeType>::subscribe(NodeType *node, std::string &topic, rmw_qos_profile_t qos, agnocast::SubscriptionOptions options)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Description
node	The rclcpp::Node to use to subscribe.
topic	The topic to subscribe to.
qos	The rmw qos profile to use to subscribe.
options	The subscription options to use to subscribe.

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subscribe() [overload 5]

void message_filters::SubscriberBase<NodeType>::subscribe()

Re-subscribe to a topic. Only works if this subscriber has previously been subscribed to a topic.

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unsubscribe()

void message_filters::SubscriberBase<NodeType>::unsubscribe()

Force immediate unsubscription of this subscriber from its topic.

agnocast::message_filters::Subscriber<M>

Extends: agnocast::message_filters::SubscriberBase< rclcpp::Node >, agnocast::message_filters::SimpleFilter< M >

Agnocast subscription filter. This class acts as a highest-level filter, simply passing messages from an agnocast subscription through to the filters which have connected to it. When this object is destroyed it will unsubscribe from the agnocast subscription. The Subscriber object is templated on the type of message being subscribed to.

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Subscriber()

message_filters::Subscriber<M, NodeType>::Subscriber(NodePtr node, std::string &topic, rmw_qos_profile_t qos)

Constructor. See the agnocast::create_subscription() variants for more information on the parameters

Parameter	Default	Description
node	—	The rclcpp::Node::SharedPtr to use to subscribe.
topic	—	The topic to subscribe to.
qos	rmw_qos_profile_default	(optional) The rmw qos profile to use to subscribe.

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Subscriber() [overload 2]

message_filters::Subscriber<M, NodeType>::Subscriber(NodePtr node, std::string &topic, rmw_qos_profile_t qos, agnocast::SubscriptionOptions options)

Constructor. See the agnocast::create_subscription() variants for more information on the parameters

Parameter	Description
node	The rclcpp::Node::SharedPtr to use to subscribe.
topic	The topic to subscribe to.
qos	The rmw qos profile to use to subscribe.
options	The subscription options to use to subscribe.

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Subscriber() [overload 3]

message_filters::Subscriber<M, NodeType>::Subscriber()

Empty constructor, use subscribe() to subscribe to a topic.

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subscribe()

void message_filters::Subscriber<M, NodeType>::subscribe(NodePtr node, std::string &topic, rmw_qos_profile_t qos)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Default	Description
node	—	The rclcpp::Node::SharedPtr to use to subscribe.
topic	—	The topic to subscribe to.
qos	rmw_qos_profile_default	(optional) The rmw qos profile to use to subscribe.

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subscribe() [overload 2]

void message_filters::Subscriber<M, NodeType>::subscribe(NodeType *node, std::string &topic, rmw_qos_profile_t qos)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Default	Description
node	—	The rclcpp::Node to use to subscribe.
topic	—	The topic to subscribe to.
qos	rmw_qos_profile_default	(optional) The rmw qos profile to use to subscribe.

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subscribe() [overload 3]

void message_filters::Subscriber<M, NodeType>::subscribe(NodePtr node, std::string &topic, rmw_qos_profile_t qos, agnocast::SubscriptionOptions options)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Description
node	The rclcpp::Node::SharedPtr to use to subscribe.
topic	The topic to subscribe to.
qos	The rmw qos profile to use to subscribe.
options	The subscription options to use to subscribe.

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subscribe() [overload 4]

void message_filters::Subscriber<M, NodeType>::subscribe(NodeType *node, std::string &topic, rmw_qos_profile_t qos, agnocast::SubscriptionOptions options)

Subscribe to a topic. If this Subscriber is already subscribed to a topic, this function will first unsubscribe.

Parameter	Description
node	The rclcpp::Node to use to subscribe.
topic	The topic to subscribe to.
qos	The rmw qos profile to use to subscribe.
options	The subscription options to use to subscribe.

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subscribe() [overload 5]

void message_filters::Subscriber<M, NodeType>::subscribe()

Re-subscribe to a topic. Only works if this subscriber has previously been subscribed to a topic.

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unsubscribe()

void message_filters::Subscriber<M, NodeType>::unsubscribe()

Force immediate unsubscription of this subscriber from its topic.

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getTopic()

std::string message_filters::Subscriber<M, NodeType>::getTopic() const

Return the topic name this subscriber is subscribed to.

Returns	Topic name string.

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getSubscriber()

agnocast::Subscription::SharedPtr message_filters::Subscriber<M, NodeType>::getSubscriber() const

Returns the internal agnocast::Subscription::SharedPtr object.

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connectInput()

void message_filters::Subscriber<M, NodeType>::connectInput(F &f)

No-op. Provided for compatibility with message_filters::Chain.

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add()

void message_filters::Subscriber<M, NodeType>::add(EventType &e)

No-op. Provided for compatibility with message_filters::Chain.

agnocast::message_filters::Synchronizer<Policy>

Extends: noncopyable, Policy

Synchronizes messages from 2–9 input filters based on a time policy. Drop-in replacement for message_filters::Synchronizer. When matching messages are found according to the policy, the registered callback is invoked with one agnocast::ipc_shared_ptr per input.

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Synchronizer()

message_filters::Synchronizer<Policy>::Synchronizer(F0 &f0, F1 &f1)

Construct a synchronizer with 2-9 input filters.

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Synchronizer() [overload 2]

message_filters::Synchronizer<Policy>::Synchronizer()

Construct an unconnected synchronizer. Call connectInput() to connect filters.

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Synchronizer() [overload 3]

message_filters::Synchronizer<Policy>::Synchronizer(Policy &policy, F0 &f0, F1 &f1)

Construct a synchronizer with a policy and 2–9 input filters.

Parameter	Description
policy	Sync policy instance.
f0	First input filter.
f1	Second input filter.

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Synchronizer() [overload 4]

message_filters::Synchronizer<Policy>::Synchronizer(Policy &policy)

Construct a synchronizer with a policy but no input filters.

Parameter	Description
policy	Sync policy instance.

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connectInput()

void message_filters::Synchronizer<Policy>::connectInput(F0 &f0, F1 &f1)

Connect 2–9 input filters to this synchronizer. Replaces any previous connections.

Parameter	Description
f0	First input filter.
f1	Second input filter.

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registerCallback()

Connection message_filters::Synchronizer<Policy>::registerCallback(C &callback)

Register a callback invoked when matching messages are found.

Parameter	Description
callback	Callback to register.
Returns	Connection object for disconnecting.

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registerCallback() [overload 2]

Connection message_filters::Synchronizer<Policy>::registerCallback(C &callback)

Register a const callback.

Parameter	Description
callback	Callback to register.
Returns	Connection object.

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registerCallback() [overload 3]

Connection message_filters::Synchronizer<Policy>::registerCallback(C &callback, T *t)

Register a member function callback.

Parameter	Description
callback	Member function pointer.
t	Object to call the member function on.
Returns	Connection object.

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registerCallback() [overload 4]

Connection message_filters::Synchronizer<Policy>::registerCallback(C &callback, T *t)

Register a member function callback.

Parameter	Description
callback	Member function pointer.
t	Object to call the member function on.
Returns	Connection object.

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setName()

void message_filters::Synchronizer<Policy>::setName(std::string &name)

Set the name of this synchronizer (for debugging).

Parameter	Description
name	Name string.

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getName()

std::string & message_filters::Synchronizer<Policy>::getName()

Return the name of this synchronizer.

Returns	Name string.

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getPolicy()

Policy * message_filters::Synchronizer<Policy>::getPolicy()

Return a pointer to the sync policy. Use this to configure policy parameters after construction (e.g., sync.getPolicy()->setAgePenalty(0.5) ).

Returns	Pointer to the policy object.

agnocast::message_filters::PassThrough<M>

Extends: agnocast::message_filters::SimpleFilter< M >

Simple passthrough filter. What comes in goes out immediately.

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PassThrough()

message_filters::PassThrough<M>::PassThrough()

Construct an unconnected PassThrough filter.

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PassThrough() [overload 2]

message_filters::PassThrough<M>::PassThrough(F &f)

Construct and connect to an upstream filter.

Parameter	Description
f	Upstream filter to connect.

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connectInput()

void message_filters::PassThrough<M>::connectInput(F &f)

Connect an upstream filter so its output is forwarded through this PassThrough.

Parameter	Description
f	Upstream filter.

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add()

void message_filters::PassThrough<M>::add(MConstPtr &msg)

Feed a message to all downstream filters.

Parameter	Description
msg	Message to forward.

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add() [overload 2]

void message_filters::PassThrough<M>::add(EventType &evt)

Feed a message event to all downstream filters.

Parameter	Description
evt	Event to forward.

agnocast::message_filters::sync_policies::ExactTime<M0, M1, ...>

Extends: agnocast::message_filters::PolicyBase< M0, M1, NullType, NullType, NullType, NullType, NullType, NullType, NullType >

Sync policy that matches messages with exactly equal timestamps. Supports 2-9 message types.

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ExactTime()

message_filters::sync_policies::ExactTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::ExactTime(uint32_t queue_size)

Construct with a queue size.

Parameter	Description
queue_size	Maximum number of messages to buffer per input.

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ExactTime() [overload 2]

message_filters::sync_policies::ExactTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::ExactTime(ExactTime &e)

Copy constructor.

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operator=()

ExactTime & message_filters::sync_policies::ExactTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::operator=(ExactTime &rhs)

Copy assignment.

Returns	Reference to *this.

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registerDropCallback()

Connection message_filters::sync_policies::ExactTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::registerDropCallback(C &callback)

Register a callback invoked when messages are dropped due to queue overflow or missing matches.

Parameter	Description
callback	Callback to register.
Returns	Connection object for disconnecting.

agnocast::message_filters::sync_policies::ApproximateTime<M0, M1, ...>

Extends: agnocast::message_filters::PolicyBase< M0, M1, NullType, NullType, NullType, NullType, NullType, NullType, NullType >

Sync policy that matches messages with approximately equal timestamps using cost-based optimization. Supports 2-9 message types.

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ApproximateTime()

message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::ApproximateTime(uint32_t queue_size)

Construct with a queue size.

Parameter	Description
queue_size	Maximum number of messages to buffer per input.

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ApproximateTime() [overload 2]

message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::ApproximateTime(ApproximateTime &e)

Copy constructor.

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operator=()

ApproximateTime & message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::operator=(ApproximateTime &rhs)

Copy assignment.

Returns	Reference to *this.

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setAgePenalty()

void message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::setAgePenalty(double age_penalty)

Set the weight given to message age when computing match cost. Higher values prefer newer messages.

Parameter	Description
age_penalty	Age penalty weight (must be >= 0, default: 0.1).

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setInterMessageLowerBound()

void message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::setInterMessageLowerBound(int i, rclcpp::Duration lower_bound)

Set the minimum expected interval between consecutive messages for a given input.

Parameter	Description
i	Input index (0-based).
lower_bound	Minimum expected interval (default: 0, auto-estimated).

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setMaxIntervalDuration()

void message_filters::sync_policies::ApproximateTime<M0, M1, M2, M3, M4, M5, M6, M7, M8>::setMaxIntervalDuration(rclcpp::Duration max_interval_duration)

Set the maximum allowed time difference between matched messages.

Parameter	Description
max_interval_duration	Maximum interval (default: no limit).

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Full Example

#include "agnocast/agnocast.hpp"

using MsgA = sensor_msgs::msg::Image;
using MsgB = sensor_msgs::msg::CameraInfo;
using Policy = agnocast::message_filters::sync_policies::ExactTime<MsgA, MsgB>;

class MySyncNode : public rclcpp::Node {
  agnocast::message_filters::Subscriber<MsgA> sub_a_;
  agnocast::message_filters::Subscriber<MsgB> sub_b_;
  agnocast::message_filters::Synchronizer<Policy> sync_;

  void callback(const agnocast::ipc_shared_ptr<const MsgA> & a,
                const agnocast::ipc_shared_ptr<const MsgB> & b) {
    // Process synchronized messages
  }

public:
  MySyncNode() : Node("sync_node"),
    sub_a_(this, "/image"),
    sub_b_(this, "/camera_info"),
    sync_(Policy(10), sub_a_, sub_b_) {
    sync_.registerCallback(&MySyncNode::callback, this);
  }
};