czml3

From the official CZML Guide:

CZML is a JSON format for describing a time-dynamic graphical scene, primarily for display in a web browser running Cesium. It describes lines, points, billboards, models, and other graphical primitives, and specifies how they change with time.

czml3 aims to make the process of writing CZML files in Python easy by:

• Type checking properties
• Coercion of data to their required format
• Forbidding unrecognised properties
• Creating minimal CZML files
• Fast JSON serialization

Installation

You can install czml3 using pip:

pip install czml3

or conda:

conda install czml3 --channel conda-forge

Examples

Creating a document

A CZML document is a list of packets, which have several properties. Recreating the blue box from Cesium sandcastle's CZML Box:

from czml3 import (
    Box,
    BoxDimensions,
    Color,
    Document,
    Material,
    Packet,
    Position,
    SolidColorMaterial,
)

packet_box = Packet(
    id="my_id",
    position=Position(cartographicDegrees=[-114.0, 40.0, 300000.0]),
    box=Box(
        dimensions=BoxDimensions(cartesian=[400000.0, 300000.0, 500000.0]),
        material=Material(
            solidColor=SolidColorMaterial(color=Color(rgba=[0, 0, 255, 255]))
        ),
    ),
)
doc = Document(packets=[packet_box])
print(doc)

Output

[
    {
        "id": "document",
        "name": "document",
        "version": "1.0"
    },
    {
        "id": "my_id",
        "position": {
            "cartographicDegrees": [
                -114.0,
                40.0,
                300000.0
            ]
        },
        "box": {
            "dimensions": {
                "cartesian": [
                    400000.0,
                    300000.0,
                    500000.0
                ]
            },
            "material": {
                "solidColor": {
                    "color": {
                        "rgba": [
                            0,
                            0,
                            255,
                            255
                        ]
                    }
                }
            }
        }
    }
]

The document packet

Document adds the required preamble packet (id="document") when you don't supply one. To name the document or set its clock, pass your own preamble packet first:

from czml3 import CZML_VERSION, Document, Packet

doc = Document(
    packets=[
        Packet(id="document", name="My scene", version=CZML_VERSION),
        packet_box,
    ]
)

Imports

The most common classes can be imported from czml3 directly; everything else lives in czml3.properties, czml3.types and czml3.enums.

Data coercion

czml3 uses pydantic for all classes, so it is able to coerce data to their right type.

Plain lists are converted to the matching CZML value type, so BoxDimensions(cartesian=[...]) is equivalent to BoxDimensions(cartesian=Cartesian3Value(values=[...])).

Arrays are coerced too. For example, the following creates a Position property of doubles using a numpy array of integer type:

import numpy as np
from czml3.properties import Position

print(Position(cartographicDegrees=np.array([-114, 40, 300000], dtype=int)))

{
    "cartographicDegrees": [
        -114.0,
        40.0,
        300000.0
    ]
}

Saving and loading

doc.save("scene.czml")
doc = Document.load("scene.czml")

Viewing a document

In Jupyter, displaying a Document renders it in an interactive Cesium viewer.

Outside notebooks, write the same viewer as a standalone page:

doc.save_html("scene.html")

• ion_token= uses Cesium ion imagery and terrain.
• cesium_version= chooses the CesiumJS release.

Browsers block Cesium's web workers on pages opened straight from disk (file://), so serve the file over HTTP and open http://localhost:8000/scene.html:

python -m http.server

Contributing

You want to contribute? Awesome! There are lots of CZML properties and validations that we still did not implement, which can be found here.

All ideas welcome!