MS RFC 137: Native FlatGeobuf support

Author:

Björn Harrtell

Contact:

bjorn.harrtell@gmail.com

Author:

Jeff McKenna

Contact:

jmckenna@gatewaygeomatics.com

Last Updated:

2022-06-24

Version:

MapServer 8.0

Status:

Adopted

1. Background

../../_images/flatgeobuf.jpg

FlatGeobuf is an optimized binary encoding for vectors based on Flatbuffers, that focuses on read/query performance by leveraging a Packed Hilbert R-Tree spatial index, that enables fast bounding box spatial filtering. FlatGeobuf performance has helped make it become one of the chosen formats for streaming spatial data through HTTP / “the cloud”.

2. Current Status through OGR

  • Since GDAL 3.1.0, FlatGeobuf access is available in MapServer through OGR

    CONNECTIONTYPE OGR
    CONNECTION "name.fgb"
    DATA "layername"
    CONNECTIONOPTIONS
      "VERIFY_BUFFERS" "NO" # for maximum performance
    END
    
  • There is some performance overhead connecting through OGR. The following rudimentary benchmark shows some overhead for shapefile through OGR

    Shapefile (native) 0.010s
    FlatGeobuf (OGR)   0.013s
    Shapefile (OGR)    0.023s
    GeoPackage (OGR)   0.042s
    SpatiaLite (OGR)   0.045s
    PostGIS (native)   0.053s
    GeoJSON (OGR)      0.089s
    
    environment: MapServer-main + GDAL 3.4.3 (MS4W/Windows)
    

3. Proposed enhancement

  • add FlatGeobuf as a native format for MapServer

    CONNECTIONTYPE flatgeobuf
    DATA "name.fgb"
    
  • FlatGeobuf C++ implementation is small and doesn’t require any dependencies

  • Flatbuffers source will be included

  • initial implementation will be read access only

3.1 Backwards Compatibility

Not applicable

3.2 Performance Implications

As mentioned above, this should give a performance boost by reading direct from the FlatGeobuf file. More benchmarks will be included here during the testing of this Pull Request. For example, here is an updated benchmark run on 2022-05-16 (note that this is for world extents, with country labels) :

FlatGeobuf (native) 0.008s
Shapefile (native)  0.010s
FlatGeobuf (OGR)    0.013s
Shapefile (OGR)     0.023s
GeoPackage (OGR)    0.042s
SpatiaLite (OGR)    0.045s
PostGIS (native)    0.053s
GeoJSON (OGR)       0.089s

environment: MapServer-main + GDAL 3.4.3 (MS4W/Windows)

3.3 Limitations

  1. This will be read access only, initially. This means that tricks such as setting an OUTPUTFORMAT for direct FlatGeobuf output from MapServer, will only work through OGR, for now.

  2. The VERIFY_BUFFERS driver option of FlatGeobuf is not implemented through this native driver (it is exposed through the OGR connection in MapServer, if need be). Specifically this means that currently the value of VERIFY_BUFFERS is equivalent to NO for this native driver, at the moment.

3.4 Security Concerns

There are no known security concerns at the moment.

3.5 MapScript

The new format has been exposed through layerObj->setConnectionType().

4. Implementation Details

4.1 Affected files

  • new files will be stored in: /flatgeobuf/

  • included files will be stored in: /flatgeobuf/include/

  • mapflatgeobuf.c: main logic

  • mapfile.c: add new CONNECTIONTYPE

  • test has added in /msautotest/misc/flatgeobuf.map

  • MapScript test has been added in /msautotest/php/layerObjTest.php

4.2 Ticket Reference

4.3 Documentation

5. Voting History

+1 from JeromeB, TomK, SethG, MikeS, LarsS (community vote), JeffM
0 from EvenR