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Minor readme improvements #83

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85 changes: 38 additions & 47 deletions README.md
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# MapLibre Tiles (MLT)

The MLT format is mainly inspired by the [Mapbox Vector Tile (MVT)](https://github.com/mapbox/vector-tile-spec) specification, but has been redesigned from the ground
up to primarily improve on the following topics:
- **Improved compression ratio**: up to 6x on large tiles, based on a column oriented layout with (custom) lightweight encodings
- **Better decoding performance**: fast lightweight encodings which can be used in combination with SIMD/vectorization instructions
- **Support for linear referencing and m-values**: to efficiently support the upcoming next generation source formats such as Overture Maps (GeoParquet)
- **Support for a more complex type system**: Including nested properties, lists and maps
- **Support for 3D coordinates**
- **Improved processing performance**: Based on an in-memory format that can be processed efficiently on the CPU and GPU and loaded directly
into GPU buffers partially (like polygons in WebGL) or completely (in case of WebGPU compute shader usage) without additional processing


## Comparison with Mapbox Vector Tiles

In the following, the size of MLT and MVT files are compared based on a selected set of representative tiles of an
OpenMapTiles scheme based OSM dataset. While showing an up to factor 6 reduction in size on large tiles, initial tests also
showed equal or mostly even better (between 2x and 3x even without the usage of SIMD) decoding performance compared
to MVT in the browser.


| Zoom level | Tile indices <br/>(minX,maxX,minY,maxY) | Tile Size Reduction (%) |
|------------|-----------------------------------------|----------------------|
| 2 | 2,2,2,2 | 53 |
| 3 | 4,4,5,5 | 48 |
| 4 | | 80 |
| 5 | 16,17,20,21 | 81 |
| 6 | 32,34,41,42 | 76 |
| 7 | 66,68,83,85 | 74 |
| 8 | 132, 135, 170, 171 | 74 |
| 9 | 264, 266, 340, 342 | 68 |
| 10 | 530, 533, 682, 684 | 60 |
| 12 | 2130, 2134, 2733, 2734 | 65 |
| 13 | 4264, 4267, 5467, 5468 | 50 |
| 14 | 8296, 8300, 10748, 10749 | 59 |

## Information about the repository

> **_Notice:_** This repository is still in the active research and development phase and is not ready for production use.
It contains experimental research code that is subject to change.

This repository has the following directory structure:
- ``spec``: Contains a rough first (yet incomplete specified) draft of the MLT specification
- ``test``: Contains a set of test tilesets and expected MLT files.
- Language specific implementations:
- ``java``: Contains a Java encoder for converting MVT to MLT files as well as decoder for converting
the MLT storage into the in-memory format.
- ``js``: Contains an experimental Javascript decoder.
- ``rust``: Contains an experimental Rust decoder.
The MLT format is mainly inspired by the [MVT format](https://github.com/mapbox/vector-tile-spec) specification, but has been redesigned from the ground up to improve the following areas:

- **Improved compression ratio** - up to 6x on large tiles, based on a column oriented layout with (custom) lightweight encodings
- **Better decoding performance** - fast lightweight encodings which can be used in combination with SIMD/vectorization instructions
- **Support for linear referencing and m-values** to efficiently support the upcoming next generation source formats such as Overture Maps (GeoParquet)
- **Support 3D coordinates**, i.e. elevation
- **Support complex types**, including nested properties, lists and maps
- **Improved processing performance**: Based on an in-memory format that can be processed efficiently on the CPU and GPU and loaded directly into GPU buffers partially (like polygons in WebGL) or completely (in case of WebGPU compute shader usage) without additional processing

> [!CAUTION]
> This format is still in the active research and development phase and is not ready for production use.

## Comparing with MVT

In the following, the size of MLT and MVT files are compared based on a selected set of representative tiles of an OpenMapTiles scheme based OSM dataset. While showing an up to factor 6 reduction in size on large tiles, initial tests also showed equal or mostly even better (between 2x and 3x even without the usage of SIMD) decoding performance compared to MVT in the browser.

| Zoom | Tile indices <br/>(minX,maxX,minY,maxY) | Tile Size Reduction |
|------|-----------------------------------------|---------------------|
| 2 | 2, 2, 2, 2 | 53% |
| 3 | 4, 4, 5, 5 | 48% |
| 4 | | 80% |
| 5 | 16, 17, 20, 21 | 81% |
| 6 | 32, 34, 41, 42 | 76% |
| 7 | 66, 68, 83, 85 | 74% |
| 8 | 132, 135, 170, 171 | 74% |
| 9 | 264, 266, 340, 342 | 68% |
| 10 | 530, 533, 682, 684 | 60% |
| 12 | 2130, 2134, 2733, 2734 | 65% |
| 13 | 4264, 4267, 5467, 5468 | 50% |
| 14 | 8296, 8300, 10748, 10749 | 59% |

## Directory Structure

- `/spec` MLT specification and related documentation
- `/test` Test MVT tiles and the expected MLT conversion results
- `/java` Java encoder for converting MVT to MLT, as well as a decoder parsing MLT to an in-memory representation.
- `/js` Javascript decoder
- `/rust` Rust decoder