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https://github.com/kylebarron/quantized-mesh-encoder

A fast Python Quantized Mesh encoder
https://github.com/kylebarron/quantized-mesh-encoder

cesium deck-gl mesh mesh-processing quantized-mesh terrain terrain-mesh-generator

Last synced: 26 days ago
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A fast Python Quantized Mesh encoder

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# quantized-mesh-encoder



[![Build Status](https://travis-ci.org/kylebarron/quantized-mesh-encoder.svg?branch=master)](https://travis-ci.org/kylebarron/quantized-mesh-encoder)



A fast Python [Quantized Mesh][quantized_mesh_spec] encoder. Encodes a mesh with

100k coordinates and 180k triangles in 20ms. [Example viewer][example].



[![][image_url]][example]



[image_url]: https://raw.githubusercontent.com/kylebarron/quantized-mesh-encoder/master/assets/no-texture-example.jpg

[example]: https://kylebarron.dev/quantized-mesh-encoder



The Grand Canyon and Walhalla Plateau. The mesh is created using

[`pydelatin`][pydelatin] or [`pymartini`][pymartini], encoded using

`quantized-mesh-encoder`, served on-demand using [`dem-tiler`][dem-tiler], and

rendered with [deck.gl](https://deck.gl).



[pymartini]: https://github.com/kylebarron/pymartini

[pydelatin]: https://github.com/kylebarron/pydelatin

[dem-tiler]: https://github.com/kylebarron/dem-tiler



## Overview



[Quantized Mesh][quantized_mesh_spec] is a format to encode terrain meshes for

efficient client-side terrain rendering. Such files are supported in

[Cesium][cesium] and [deck.gl][deck.gl].



This library is designed to support performant server-side on-demand terrain

mesh generation.



[quantized_mesh_spec]: https://github.com/CesiumGS/quantized-mesh

[cesium]: https://github.com/CesiumGS/cesium

[deck.gl]: https://deck.gl/



## Install



With pip:



```

pip install quantized-mesh-encoder

```



or with Conda:



```

conda install -c conda-forge quantized-mesh-encoder

```



## Using



### API



#### `quantized_mesh_encoder.encode`



Arguments:



- `f`: a writable file-like object in which to write encoded bytes

- `positions`: (`array[float]`): either a 1D Numpy array or a 2D Numpy array of

  shape `(-1, 3)` containing 3D positions.

- `indices` (`array[int]`): either a 1D Numpy array or a 2D Numpy array of shape

  `(-1, 3)` indicating triples of coordinates from `positions` to make

  triangles. For example, if the first three values of `indices` are `0`, `1`,

  `2`, then that defines a triangle formed by the first 9 values in `positions`,

  three for the first vertex (index `0`), three for the second vertex, and three

  for the third vertex.



Keyword arguments:



- `bounds` (`List[float]`, optional): a list of bounds, `[minx, miny, maxx,

  maxy]`. By default, inferred as the minimum and maximum values of `positions`.

- `sphere_method` (`str`, optional): As part of the header information when

  encoding Quantized Mesh, it's necessary to compute a [_bounding

  sphere_][bounding_sphere], which contains all positions of the mesh.

  `sphere_method` designates the algorithm to use for creating the bounding

  sphere. Must be one of `'bounding_box'`, `'naive'`, `'ritter'` or `None`.

  Default is `None`.

    - `'bounding_box'`: Finds the bounding box of all positions, then defines

      the center of the sphere as the center of the bounding box, and defines

      the radius as the distance back to the corner. This method produces the

      largest bounding sphere, but is the fastest: roughly 70 µs on my computer.

    - `'naive'`: Finds the bounding box of all positions, then defines the

      center of the sphere as the center of the bounding box. It then checks the

      distance to every other point and defines the radius as the maximum of

      these distances. This method will produce a slightly smaller bounding

      sphere than the `bounding_box` method when points are not in the 3D

      corners. This is the next fastest at roughly 160 µs on my computer.

    - `'ritter'`: Implements the Ritter Method for bounding spheres. It first

      finds the center of the longest span, then checks every point for

      containment, enlarging the sphere if necessary. This _can_ produce smaller

      bounding spheres than the naive method, but it does not always, so often

      both are run, see next option. This is the slowest method, at roughly 300

      µs on my computer.

    - `None`: Runs both the naive and the ritter methods, then returns the

      smaller of the two. Since this runs both algorithms, it takes around 500

      µs on my computer

- `ellipsoid` (`quantized_mesh_encoder.Ellipsoid`, optional): ellipsoid defined by its semi-major `a`

   and semi-minor `b` axes.

   Default: WGS84 ellipsoid.

- extensions: list of extensions to encode in quantized mesh object. These must be `Extension` instances. See [Quantized Mesh Extensions](#quantized-mesh-extensions).



[bounding_sphere]: https://en.wikipedia.org/wiki/Bounding_sphere



#### `quantized_mesh_encoder.Ellipsoid`



Ellipsoid used for mesh calculations.



Arguments:



- `a` (`float`): semi-major axis

- `b` (`float`): semi-minor axis



#### `quantized_mesh_encoder.WGS84`



Default [WGS84 ellipsoid](https://en.wikipedia.org/wiki/World_Geodetic_System#1984_version). Has a semi-major axis `a` of 6378137.0 meters and semi-minor axis `b` of 6356752.3142451793 meters.



#### Quantized Mesh Extensions



There are a variety of [extensions](https://github.com/CesiumGS/quantized-mesh#extensions) to the Quantized Mesh spec.



##### `quantized_mesh_encoder.VertexNormalsExtension`



Implements the [Terrain Lighting](https://github.com/CesiumGS/quantized-mesh#terrain-lighting) extension. Per-vertex normals will be generated from your mesh data.



Keyword Arguments:



- `indices`: mesh indices

- `positions`: mesh positions

- `ellipsoid`: instance of Ellipsoid class, default: WGS84 ellipsoid



##### `quantized_mesh_encoder.WaterMaskExtension`



Implements the [Water Mask](https://github.com/CesiumGS/quantized-mesh#water-mask) extension.



Keyword Arguments:



- `data` (`Union[np.ndarray, np.uint8, int]`): Data for water mask.



##### `quantized_mesh_encoder.MetadataExtension`



Implements the [Metadata](https://github.com/CesiumGS/quantized-mesh#metadata) extension.



- `data` (`Union[Dict, bytes]`): Metadata data to encode. If a dictionary, `json.dumps` will be called to create bytes in UTF-8 encoding.



### Examples



#### Write to file



```py

from quantized_mesh_encoder import encode

with open('output.terrain', 'wb') as f:

    encode(f, positions, indices)

```



Quantized mesh files are usually saved gzipped. An easy way to create a gzipped

file is to use `gzip.open`:



```py

import gzip

from quantized_mesh_encoder import encode

with gzip.open('output.terrain', 'wb') as f:

    encode(f, positions, indices)

```



#### Write to buffer



It's also pretty simple to write to an in-memory buffer instead of a file



```py

from io import BytesIO

from quantized_mesh_encoder import encode

with BytesIO() as bio:

    encode(bio, positions, indices)

```



Or to gzip the in-memory buffer:



```py

import gzip

from io import BytesIO

with BytesIO() as bio:

    with gzip.open(bio, 'wb') as gzipf:

        encode(gzipf, positions, indices)

```



#### Alternate Ellipsoid



By default, the [WGS84

ellipsoid](https://en.wikipedia.org/wiki/World_Geodetic_System#1984_version) is

used for all calculations. An alternate ellipsoid may be useful for non-Earth

planetary bodies.



```py

from quantized_mesh_encoder import encode, Ellipsoid



# From https://ui.adsabs.harvard.edu/abs/2010EM%26P..106....1A/abstract

mars_ellipsoid = Ellipsoid(3_395_428, 3_377_678)



with open('output.terrain', 'wb') as f:

    encode(f, positions, indices, ellipsoid=mars_ellipsoid)

```



#### Quantized Mesh Extensions



```py

from quantized_mesh_encoder import encode, VertexNormalsExtension, MetadataExtension



vertex_normals = VertexNormalsExtension(positions=positions, indices=indices)

metadata = MetadataExtension(data={'hello': 'world'})



with open('output.terrain', 'wb') as f:

    encode(f, positions, indices, extensions=(vertex_normals, metadata))

```



#### Generating the mesh



To encode a mesh into a quantized mesh file, you first need a mesh! This project

was designed to be used with [`pydelatin`][pydelatin] or

[`pymartini`][pymartini], fast elevation heightmap to terrain mesh generators.



```py

import quantized_mesh_encoder

from imageio import imread

from pymartini import decode_ele, Martini, rescale_positions

import mercantile



png = imread(png_path)

terrain = decode_ele(png, 'terrarium')

terrain = terrain.T

martini = Martini(png.shape[0] + 1)

tile = martini.create_tile(terrain)

vertices, triangles = tile.get_mesh(10)



# Use mercantile to find the bounds in WGS84 of this tile

bounds = mercantile.bounds(mercantile.Tile(x, y, z))



# Rescale positions to WGS84

rescaled = rescale_positions(

    vertices,

    terrain,

    bounds=bounds,

    flip_y=True

)



with BytesIO() as f:

    quantized_mesh_encoder.encode(f, rescaled, triangles)

    f.seek(0)

    return ("OK", "application/vnd.quantized-mesh", f.read())

```



You can also look at the source of

[`_mesh()`](https://github.com/kylebarron/dem-tiler/blob/5b50a216a014eb32febee84fe3063ca99e71c7f6/dem_tiler/handlers/app.py#L234)

in [`dem-tiler`][dem-tiler] for a working reference.



## License



Much of this code is ported or derived from

[`quantized-mesh-tile`][quantized-mesh-tile] in some way. `quantized-mesh-tile`

is also released under the MIT license.



[pymartini]: https://github.com/kylebarron/pymartini

[quantized-mesh-tile]: https://github.com/loicgasser/quantized-mesh-tile