Param for lowering used channel count

README.rst

@@ -241,6 +241,7 @@ You can also optionally specify:
 * ``lidar_mode:=<mode>`` where mode is one of ``512x10``, ``512x20``, ``1024x10``, ``1024x20``, or
   ``2048x10``, and
 * ``viz:=true`` to visualize the sensor output, if you have the rviz ROS package installed
+* ``channel_reduction_ratio:=<int>`` to reduce the amount of channels used for the output cloud. So a 128 beam lidar with a channel_reduction_ratio of 4 would result in a simulated 32 beam lidar. (Value has to be 2^n)
 
 
 Recording Data

ouster_ros/include/ouster_ros/ros.h

@@ -63,10 +63,11 @@ sensor_msgs::Imu packet_to_imu_msg(const PacketMsg& pm,
  * @param ls input lidar data
  * @param return_index index of return desired starting at 0
  * @param cloud output pcl pointcloud to populate
+ * @param channel_reduction_ratio ratio at which to reduce channel count
  */
 void scan_to_cloud(const ouster::XYZLut& xyz_lut,
                    ouster::LidarScan::ts_t scan_ts, const ouster::LidarScan& ls,
-                   ouster_ros::Cloud& cloud, int return_index = 0);
+                   ouster_ros::Cloud& cloud, uint32_t channel_reduction_ratio, int return_index = 0);
 
 /**
  * Serialize a PCL point cloud to a ROS message

ouster_ros/ouster.launch

@@ -12,6 +12,7 @@
   <arg name="rviz_config" default="-d $(find ouster_ros)/viz.rviz" doc="optional rviz config file"/>
   <arg name="tf_prefix" default="" doc="namespace for tf transforms"/>
   <arg name="udp_profile_lidar" default="" doc="lidar packet profile: LEGACY, RNG19_RFL8_SIG16_NIR16_DUAL"/>
+  <arg name="channel_reduction_ratio" default="1" doc="the ratio at wich to reduce channel count, can be used to simulate a lower beam count lidar (VALUE MUST BE 2^n)"/>
 
   <node pkg="ouster_ros" name="os_node" type="os_node" output="screen" required="true">
     <param name="~/lidar_mode" type="string" value="$(arg lidar_mode)"/>
@@ -30,6 +31,13 @@
     <remap from="~/lidar_packets" to="/os_node/lidar_packets"/>
     <remap from="~/imu_packets" to="/os_node/imu_packets"/>
     <param name="~/tf_prefix" value="$(arg tf_prefix)"/>
+    <param name="~/channel_reduction_ratio" value="$(arg channel_reduction_ratio)"/>
+  </node>
+
+  <node pkg="ouster_ros" type="img_node" name="img_node" output="screen" required="false">
+    <remap from="~/os_config" to="/os_node/os_config"/>
+    <remap from="~/points" to="/os_cloud_node/points"/>
+    <param name="~/channel_reduction_ratio" value="$(arg channel_reduction_ratio)"/>
   </node>
 
   <node if="$(arg viz)" pkg="rviz" name="rviz" type="rviz" args="$(arg rviz_config)" output="screen" required="true" />

ouster_ros/src/img_node.cpp

@@ -52,6 +52,8 @@ int main(int argc, char** argv) {
     ros::init(argc, argv, "img_node");
     ros::NodeHandle nh("~");
 
+    uint32_t channel_reduction_ratio = nh.param("channel_reduction_ratio", 1);
+
     ouster_ros::OSConfigSrv cfg{};
     auto client = nh.serviceClient<ouster_ros::OSConfigSrv>("os_config");
     client.waitForExistence();
@@ -61,7 +63,7 @@ int main(int argc, char** argv) {
     }
 
     auto info = sensor::parse_metadata(cfg.response.metadata);
-    size_t H = info.format.pixels_per_column;
+    size_t H = info.format.pixels_per_column / channel_reduction_ratio;
     size_t W = info.format.columns_per_frame;
 
     auto udp_profile_lidar = info.format.udp_profile_lidar;

ouster_ros/src/os_cloud_node.cpp

@@ -29,6 +29,8 @@ int main(int argc, char** argv) {
     ros::init(argc, argv, "os_cloud_node");
     ros::NodeHandle nh("~");
 
+    uint32_t channel_reduction_ratio = nh.param("channel_reduction_ratio", 1);
+
     auto tf_prefix = nh.param("tf_prefix", std::string{});
     if (!tf_prefix.empty() && tf_prefix.back() != '/') tf_prefix.append("/");
     auto sensor_frame = tf_prefix + "os_sensor";
@@ -48,6 +50,15 @@ int main(int argc, char** argv) {
     uint32_t W = info.format.columns_per_frame;
     auto udp_profile_lidar = info.format.udp_profile_lidar;
 
+    if(channel_reduction_ratio != 1){
+        if(channel_reduction_ratio <= 0) 
+            throw std::invalid_argument("channel_reduction_ratio must be greater than zero");
+        if(H <= channel_reduction_ratio)
+            throw std::invalid_argument("channel_reduction_ratio must be less than or equal to the lidar channel count");
+        if(ceil(log2(channel_reduction_ratio)) != floor(log2(channel_reduction_ratio))) 
+            throw std::invalid_argument("channel_reduction_ratio must be 2^n");
+    }
+
     const int n_returns =
         (udp_profile_lidar == sensor::UDPProfileLidar::PROFILE_LIDAR_LEGACY)
             ? 1
@@ -71,7 +82,7 @@ int main(int argc, char** argv) {
     auto xyz_lut = ouster::make_xyz_lut(info);
 
     ouster::LidarScan ls{W, H, udp_profile_lidar};
-    Cloud cloud{W, H};
+    Cloud cloud{W, H / channel_reduction_ratio};
 
     ouster::ScanBatcher batch(W, pf);
 
@@ -83,7 +94,7 @@ int main(int argc, char** argv) {
                 });
             if (h != ls.headers.end()) {
                 for (int i = 0; i < n_returns; i++) {
-                    scan_to_cloud(xyz_lut, h->timestamp, ls, cloud, i);
+                    scan_to_cloud(xyz_lut, h->timestamp, ls, cloud, channel_reduction_ratio, i);
                     lidar_pubs[i].publish(ouster_ros::cloud_to_cloud_msg(
                         cloud, h->timestamp, sensor_frame));
                 }

ouster_ros/src/ros.cpp

@@ -94,9 +94,17 @@ sensor::ChanField suitable_return(sensor::ChanField input_field, bool second) {
 
 void scan_to_cloud(const ouster::XYZLut& xyz_lut,
                    ouster::LidarScan::ts_t scan_ts, const ouster::LidarScan& ls,
-                   ouster_ros::Cloud& cloud, int return_index) {
+                   ouster_ros::Cloud& cloud, uint32_t channel_reduction_ratio, int return_index) {
+    if(channel_reduction_ratio != 1){
+        if(channel_reduction_ratio <= 0) 
+            throw std::invalid_argument("channel_reduction_ratio must be greater than zero");
+        if(ls.h <= channel_reduction_ratio)
+            throw std::invalid_argument("channel_reduction_ratio must be less than or equal to the lidar channel count");
+        if(ceil(log2(channel_reduction_ratio)) != floor(log2(channel_reduction_ratio))) 
+            throw std::invalid_argument("channel_reduction_ratio must be 2^n");
+    }
     bool second = (return_index == 1);
-    cloud.resize(ls.w * ls.h);
+    cloud.resize(ls.w * ls.h / channel_reduction_ratio);
 
     ouster::img_t<uint16_t> near_ir;
     ouster::impl::visit_field(
@@ -120,11 +128,11 @@ void scan_to_cloud(const ouster::XYZLut& xyz_lut,
 
     auto points = ouster::cartesian(range, xyz_lut);
 
-    for (auto u = 0; u < ls.h; u++) {
+    for (auto u = 0, w = 0; u < ls.h; u += channel_reduction_ratio, w++) {
         for (auto v = 0; v < ls.w; v++) {
             const auto xyz = points.row(u * ls.w + v);
             const auto ts = (ls.header(v).timestamp - scan_ts).count();
-            cloud(v, u) = ouster_ros::Point{
+            cloud(v, w) = ouster_ros::Point{
                 {{static_cast<float>(xyz(0)), static_cast<float>(xyz(1)),
                   static_cast<float>(xyz(2)), 1.0f}},
                 static_cast<float>(signal(u, v)),