Kappe

Kappe is an efficient data migration tool designed to seamlessly convert and split MCAP files.

Installation

pip install kappe

or

rye tools install kappe

Usage

Create a yaml config file containing the migrations you want to perform.

Example:

config.yaml

topic:
  mapping:
    /points: /sensor/points

Run the converter:

kappe convert --config config.yaml ./input.bag

Convert

kappe convert [-h] [--config CONFIG] [--overwrite] input output

Converts a single file or a directory of files to the MCAP format.

Topic

Rename a topic

topic:
  mapping:
    /points: /sensor/points

Remove a topic

topic:
  remove:
    - /points

Change ROS Timestamp to publish time

Change the time of the ROS Timestamp to the time the message was published.

time_offset:
  /sensor/points:
    pub_time: True

Add a time offset to ROS Timestamp

Add 15 seconds to the ROS Timestamp.

time_offset:
  /sensor/points:
    sec: 15
    nanosec: 0

Pointcloud

Remove zero points from PointCloud2

point_cloud:
  /sensor/points:
    remove_zero: true

Rotate a pointcloud

point_cloud:
  /sensor/points:
    rotation:
      euler_deg:
        - 180
        - 0
        - 0

Rename PointCloud2 field name

Changes the field name of the PointCloud2 message, from AzimuthAngle to azimuth_angle.

point_cloud:
  /sensor/points:
    field_mapping:
      AzimuthAngle: azimuth_angle

TF

To update a static transform you need to remove the old one and insert a new one.

Remove Transform

Removes all transform where the child_frame_id is test_data_frame or other_frame.

tf_static:
  remove:
    - test_data_frame
    - other_frame

Insert Static Transform

Rotation can be specified in euler_deg or quaternion

tf_static:
  insert:
    - frame_id: base
      child_frame_id: also_base

    - frame_id: base
      child_frame_id: sensor
      translation:
        x: -0.1
        y: 0
        z: 0.1
      rotation:
        euler_deg:
          - 0
          - 90
          - 0

Plugins

Kappe can be extended with plugins, for example to compress images. Source code for plugins can be found in the plugins, additional plugins can be loaded from ./plugins.

plugins:
  - name: image.CompressImage
    input_topic: /image
    output_topic: /compressed/image
    settings:
      quality: 50

Cut

usage: kappe cut [-h] --config CONFIG [--overwrite] input [output_folder]

Cuts a directory of mcaps into smaller mcaps, based on timestamp or topic.

When keep_tf_tree is set to true all splits will have the same /tf_static messages.

Split on time

keep_tf_tree: true
splits:
  - start:  1676549454.0
    end:    1676549554.0
    name:   beginning
  - start:  1676549554.0
    end:    1676549654.0
    name:   end.mcap

kappe cut --config config.yaml ./input.mcap ./output_folder

Results in a folder with the following structure:

output_folder
├── beginning.mcap
└── end.mcap

Split on topic

Splits the mcap file into multiple files, every time a message on the topic /marker is read. The file will be split before the message is read. debounce is the time in seconds that the cutter will wait before splitting the file again, default is 0.

keep_tf_tree: true
split_on_topic:
  topic: "/marker"
  debounce: 10