fix: skip empty and short decoded lidar scans (#77)

* fix: skip empty and short decoded lidar scans

Move empty and minimum-point filtering into the shared decoder path so Nebula and Seyond inputs consistently skip status-only or non-decodable packet groups without misleading conversion results.

Made-with: Cursor

* docs: drop README note about skipped scans

Keep the README focused on user-facing behavior and remove the extra note about internal scan filtering from the PR.

Made-with: Cursor

Author: otenim

src/bag_converter/include/bag_converter.hpp

@@ -44,8 +44,6 @@ namespace bag_converter
 
 namespace defaults
 {
-inline constexpr size_t min_points_per_scan = 1000;
-
 // Common configuration defaults
 inline constexpr double min_range = 0.1;
 inline constexpr double max_range = 250.0;

src/bag_converter/include/base_decoder.hpp

@@ -11,18 +11,23 @@
 
 #include "point_types.hpp"
 
+#include <rclcpp/rclcpp.hpp>
 #include <rclcpp/serialization.hpp>
 
 #include <sensor_msgs/msg/point_cloud2.hpp>
 
-#include <pcl/point_cloud.h>
-#include <pcl/point_types.h>
-
 #include <memory>
 
 namespace bag_converter::decoder
 {
 
+namespace defaults
+{
+
+inline constexpr size_t min_points_per_scan = 1000;
+
+}  // namespace defaults
+
 /**
  * @brief Abstract base class for PCD decoders using type erasure pattern
  *
@@ -49,7 +54,8 @@ class BasePCDDecoder
    * Derived classes deserialize the message internally and convert to PointCloud2.
    *
    * @param serialized_msg The serialized ROS message to decode
-   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails
+   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails, the point cloud
+   * is empty, or the point cloud contains too few points
    */
   virtual sensor_msgs::msg::PointCloud2::SharedPtr decode(
     const rclcpp::SerializedMessage & serialized_msg) = 0;
@@ -82,17 +88,33 @@ class PCDDecoder : public BasePCDDecoder
   /**
    * @brief Decode serialized message to PointCloud2 (implements PCDDecoderBase)
    *
-   * Deserializes the message and delegates to the typed decode method.
+   * Deserializes the message and delegates to the typed decode method. Returns nullptr if the
+   * decoded PointCloud2 is empty or contains too few points.
    *
    * @param serialized_msg The serialized ROS message to decode
-   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails
+   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails, the point cloud
+   * is empty, or the point cloud contains too few points
    */
   sensor_msgs::msg::PointCloud2::SharedPtr decode(
     const rclcpp::SerializedMessage & serialized_msg) override
   {
     InputScanT input_msg;
     serializer_.deserialize_message(&serialized_msg, &input_msg);
-    return decode_typed(input_msg);
+    auto decoded_msg = decode_typed(input_msg);
+    if (!decoded_msg) {
+      return nullptr;
+    }
+
+    if (decoded_msg->width == 0 || decoded_msg->data.empty()) {
+      return nullptr;
+    }
+
+    const size_t num_points = decoded_msg->width * decoded_msg->height;
+    if (num_points < defaults::min_points_per_scan) {
+      return nullptr;
+    }
+
+    return decoded_msg;
   }
 
   /**
@@ -102,10 +124,12 @@ class PCDDecoder : public BasePCDDecoder
    * Converts the input scan message of type InputScanT to a PointCloud2 message.
    *
    * @param input The input scan message to decode
-   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails
+   * @return Shared pointer to PointCloud2 message, or nullptr if decoding fails or contains no
+   * points
    */
   virtual sensor_msgs::msg::PointCloud2::SharedPtr decode_typed(const InputScanT & input) = 0;
 
+protected:
 private:
   rclcpp::Serialization<InputScanT> serializer_;
 };

src/bag_converter/src/bag_converter.cpp

@@ -496,13 +496,6 @@ ProcessMessageResult process_lidar_message(
   auto pcd_msg = dec->decode(serialized_msg);
 
   if (!pcd_msg) {
-    return ProcessMessageResult::Decoded;  // nothing to write, no stats change
-  }
-
-  const size_t num_points = pcd_msg->width * pcd_msg->height;
-  if (num_points < defaults::min_points_per_scan) {
-    RCLCPP_INFO(g_logger, "Status packets detected (skipped decoding this message)");
-    conversion_stats[topic_name].skipped_count++;
     return ProcessMessageResult::Skipped;
   }
 

src/bag_converter/src/nebula_decoder.cpp

@@ -17,6 +17,8 @@
 
 #include <rclcpp/rclcpp.hpp>
 
+#include <algorithm>
+
 namespace bag_converter::decoder::nebula
 {
 
@@ -175,11 +177,6 @@ sensor_msgs::msg::PointCloud2::SharedPtr NebulaPCDDecoder<OutputPointT>::decode_
   const nebula_msgs::msg::NebulaPackets & input)
 {
   bag_converter::msg::SeyondScan scan = nebula_packets_to_seyond_scan(input, config_.frame_id);
-
-  if (scan.packets.empty()) {
-    return nullptr;
-  }
-
   return seyond_decoder_.decode_typed(scan);
 }
 

src/bag_converter/src/seyond_decoder.cpp

@@ -80,18 +80,12 @@ sensor_msgs::msg::PointCloud2::SharedPtr SeyondPCDDecoder<OutputPointT>::decode_
     }
   }
 
-  // Check if point cloud is empty
   if (cloud_.points.empty()) {
-    RCLCPP_WARN(
-      rclcpp::get_logger("bag_converter.decoder.seyond"),
-      "Decoded point cloud is empty (no points found in scan)");
+    return nullptr;
   }
 
-  // Create PointCloud2 message
   auto pc2_msg = std::make_shared<sensor_msgs::msg::PointCloud2>();
   pcl::toROSMsg(cloud_, *pc2_msg);
-
-  // Set header timestamp from input message
   pc2_msg->header.stamp = input.header.stamp;
   pc2_msg->header.frame_id = cloud_.header.frame_id;