Conversion CityJSON <=> FlatCityBuf

Table of contents

  1. Rust CLI to manipulate FlatCityBuf files
  2. Conversion CityJSONSeq => FlatCityBuf
  3. Conversion FlatCityBuf => CityJSONSeq
  4. Inspecting FCB files

If you have CityJSON files, you first need to convert them to the CityJSONSeq format.

Rust CLI to manipulate FlatCityBuf files

We offer a CLI, written in Rust (code on GitHub) to convert FlatCityBuf files to/from different formats.

Option 1: Install from crates.io

cargo install fcb_cli

Option 2: Build from source

git clone https://github.com/cityjson/flatcitybuf.git
cd flatcitybuf/src/rust
cargo build --workspace --all-features --exclude fcb_wasm --release

The binary will be available at target/release/fcb.

Conversion CityJSONSeq => FlatCityBuf 

$ fcb ser -i delft.city.jsonl -o delft.fcb
Successfully encoded to FCB

This creates a FlatCityBuf file with spatial indexing enabled by default.

With attribute indexing

To enable fast queries on specific attributes:

$ fcb ser -i delft.city.jsonl -o delft.fcb \
  --attr-index identificatie,b3_h_dak_50p,b3_is_glas_dak \
  --attr-branching-factor 16

The --attr-index flag takes a comma-separated list of attribute names to index. The branching factor (default: 256) controls the B+tree structure – higher values mean flatter trees and faster queries but slightly larger file sizes.

Index all attributes

If you want to index every attribute found in the dataset:

$ fcb ser -i delft.city.jsonl -o delft.fcb -A
Successfully encoded to FCB

This is convenient but will increase file size and conversion time.

Filtering by bounding box

You can filter features during conversion to create a subset:

$ fcb ser -i delft.city.jsonl -o filtered.fcb \
  --bbox "84227.77,445377.33,85323.23,446334.69"
Successfully encoded to FCB

The bounding box format is: minx,miny,maxx,maxy

Conversion FlatCityBuf => CityJSONSeq

To convert an FCB file back to CityJSON Text Sequences:

$ fcb deser -i delft.fcb -o delft.city.jsonl
Successfully decoded from FCB

Inspecting FCB files

The CLI also allows us to view information about an FCB file:

$ fcb info -i delft.fcb
FCB File Info:
    File size: 6 MB
  Version: 2.0
  Features count: 1115
  bbox: Some(GeographicalExtent { min: Vector { x: 84501.5546875, y: 445805.03125, z: -3.746997833251953 }, max: Vector { x: 85675.234375, y: 446983.46875, z: 95.04200744628906 } })
  attr_index: []
  Title: 3DBAG
  Geographical extent:
    Min: [84501.5546875, 445805.03125, -3.746997833251953]
    Max: [85675.234375, 446983.46875, 95.04200744628906]