Cartographer Pose Graph

export_pose_graph.py

#!/usr/bin/env python3

# Adapted from:
#
#   https://gist.github.com/mjcarroll/f620ef8d88efc3a03711259d6fc9a578
#
# Original gist fixed to work with latest version of cartographer:
#
#   [~/sensmetry/slam/cartographer:master]λ git describe --always 
#   bcd5486
#   [~/slam/cartographer_ros:master]λ git describe --always 
#   1de03b3
#
# Requirements:
#   python3
#   protobuf==3.*
#
# Preprocessing:
#   cd cartographer
#   # rename directories starting with a number - python
#   # can't import those in a straightforward way
#   find . -name '[0-9]*' -type d -exec rename 's/2d/i2d/' {} \;
#   find . -name '[0-9]*' -type d -exec rename 's/3d/i3d/' {} \;
#   find . -iname '*.proto' -exec sed -i 's|/2d/|/i2d/|' {} \;
#   find . -iname '*.proto' -exec sed -i 's|/3d/|/i3d/|' {} \;
#   mkdir py_export
#   protoc --python_out ./py_export -I . `find . -iname '*.proto'`

import struct
import gzip
import argparse

import cartographer.mapping
from cartographer.mapping.proto.serialization_pb2 import SerializationHeader, SerializedData
from cartographer.mapping.proto.pose_graph_pb2 import PoseGraph

class PbstreamFile:
    def __init__(self, pbstream_filename):
        self.pbstream_filename = pbstream_filename
        self.pbstream_file = open(pbstream_filename, 'rb')
        assert(self.is_valid())

        self.ser_data_by_type = {}

        self.read_serialization_header()
        while self.pbstream_file:
            serdata = self.read_serialized_data()
            if serdata:
                serdata_type = serdata.WhichOneof('data')
                data = getattr(serdata, serdata_type)
                cur = self.ser_data_by_type.get(serdata_type, [])
                cur.append(data)
                self.ser_data_by_type[serdata_type] = cur
            else:
                break

    def read_chunk(self):
        sz = self.read_size()
        if sz:
            buf = self.pbstream_file.read(sz)
            buf = gzip.decompress(buf)
            return buf


    def read_serialization_header(self):
        buf = self.read_chunk()
        if buf:
            sh = SerializationHeader()
            sh.ParseFromString(buf)
            return sh

    def read_serialized_data(self):
        buf = self.read_chunk()
        if buf:
            sd = SerializedData()
            sd.ParseFromString(buf)
            return sd

    def is_valid(self):
        kMagic = [0x7b, 0x1d, 0x1f, 0x7b, 0x5b, 0xf5, 0x01, 0xdb]
        self.pbstream_file.seek(0)
        magic = self.pbstream_file.read(8)
        return all([x == y for x, y in zip(kMagic[::-1], magic)])

    def read_size(self):
        buf = self.pbstream_file.read(8)
        if len(buf) < 8:
            return 0
        return struct.unpack_from("<Q", buf)[0]


    def pose_graph(self):
        pose_graphs = self.ser_data_by_type['pose_graph']
        if pose_graphs:
            if len(pose_graphs) > 1:
                print("Warning: multiple pose graphs parsed in Serialized Data "
                      "but only one should be present. Returning the first one.")
            return pose_graphs[0]
        else:
            return None


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Process and export live SLAM results")
    parser.add_argument('pbstream_filename', type=str)
    args = parser.parse_args()
    pbf = PbstreamFile(args.pbstream_filename)
    pg = pbf.pose_graph()
    print(pg)

Actually, not
it changes "serialized_pb", too
Need to be adapted.

This don't need anymore
from cartographer.mapping.proto.pose_graph_pb2 import PoseGraph

Hi @yfyf
Sorry for trouble, but I'm having problem with understanding of how this problem can be fixed and I hoped that you could know the answer.
I followed instruction you gave here and everything work fine on preparation stage but then I try to run this script I receive following error:
Traceback (most recent call last):
File "pbstreamreader.py", line 6, in
from cartographer.mapping.proto.serialization_pb2 import SerializationHeader, SerializedData
ModuleNotFoundError: No module named 'cartographer.mapping.proto.serialization_pb2'

For installation I used official guide and I'm trying to get trajectories from map my robot created, so I don't think that problem in cartographer itself. Appreciate any hints.