Update extract_images_sync to add sec_per_frame parameter (ros-percep…

…tion#920)

Added sec_per_frame parameter to allow decimation of frames being
synchronized and captured.
fixes ros-perception#726

---------

Co-authored-by: Michael Ferguson <mfergs7@gmail.com>

image_view/scripts/extract_images_sync

@@ -42,6 +42,7 @@ import cv_bridge
 import rclpy
 
 from rclpy.node import Node
+from rclpy.duration import Duration
 from sensor_msgs.msg import Image
 from message_filters import ApproximateTimeSynchronizer, TimeSynchronizer, Subscriber
 
@@ -51,10 +52,19 @@ class ExtractImagesSync(Node):
  super().__init__('extract_images_sync')
  self.get_logger().info('Extract_Images_Sync Node has been started')
  self.seq = 0
+ self.last_frame_time = self.get_clock().now()
+
  self.fname_fmt = self.declare_parameter(
- 'filename_format', 'frame%04i_%i.jpg').value 
+ 'filename_format', 'frame%04i_%i.jpg').value
+
+ # Do not scale dynamically by default.
  self.do_dynamic_scaling = self.declare_parameter(
  'do_dynamic_scaling', False).value
+
+ # Limit the throughput to 10fps by default.
+ self.sec_per_frame = self.declare_parameter(
+ 'sec_per_frame', 0.0).value
+
  img_topics = self.declare_parameter('inputs', None).value
 
  if img_topics is None:
@@ -80,6 +90,17 @@ Typical command-line usage:
  sync.registerCallback(self.save)
 
  def save(self, *imgmsgs):
+ delay = self.get_clock().now() - self.last_frame_time
+
+ # Decimation is enabled if it is set to greater than
+ # zero. If it is enabled, exit if delay is less than
+ # the decimation rate specified.
+ if (self.sec_per_frame > 0) and (delay < Duration(seconds=self.sec_per_frame)):
+ return
+
+ # Update the current time
+ self.last_frame_time = self.get_clock().now()
+
  seq = self.seq
  bridge = cv_bridge.CvBridge()
  for i, imgmsg in enumerate(imgmsgs):