@dhi-gras/terracotta-react

React implementation of a context wrapper for abstracting away some of the logic around the Terracotta XYZ tile server.

Terracotta is a pure Python tile server that runs as a WSGI app on a dedicated webserver or as a serverless app on AWS Lambda. It is built on a modern Python 3.6 stack, powered by awesome open-source software such as Flask, Zappa, and Rasterio.

Why Terracotta-react

• Abstracts away the logic around what endpoints you should hit to get the right datasets and display them on a map. All of it through a friendly API.
• Uses the highly performant Deck.gl based on the WebGL framework.
• Includes TypeScript definitions, therefore, it prevents unpredictable type errors when used in your app. The types are available by importing them from the package.

Prerequisites

Check the peerDependencies of the terracotta-react package.

Usage

Install the package

yarn add @dhi-gras/terracotta-react

// or

npm install @dhi-gras/terracotta-react

TerracottaContextProvider

The context provider aims to offer a few state values and methods to ease the implementation of Terracotta in your project.

import React, { FC } from "react"
import TerracottaProvider from "@dhi-gras/terracotta-react"

const App: FC = () => (
	<TerracottaProvider
		host={'https://your-terracotta-host.com'} // Without the ending "/".
	>
		<AppScreen />
	</TerracottaProvider>
)

export default App

Hooks

useTerracotta

The hook helps you get the values of the context state through your react tree.

import React, { FC } from "react"
import { useTerracotta } from "@dhi-gras/terracotta-react"

const AppScreen: FC = () => {
	const { keys, isLoading, getDatasets } = useTerracotta()

	return null;
}

export default AppScreen

Provided state values and methods

keys

An object respective to the response received from the /keys endpoint of the provided terracotta host.

Example:

[
	{
		"key": "keyName",
	},
	{
		"key": "keyName",
	},
	...
]

isLoading

A boolean value that represents the loading state of the provider. The value changes to true when making requests to various terracotta endpoints.

getDatasets

A method that returns a Promise by making a call to the /datasets endpoint. It can take in an argument containing the query parameters used for filtering through the available datasets from the provided Terracotta host.

For example, in the following call, the method will try to query the terracotta datasets for the project_id: 2 including the type: preprocess and type: postprocess with that id.

const { getDatasets } = useTerracotta()

const handleDatasets = async () => {
	try{
		const response = await getDatasets({
			project_id: 2,
			type: [ 'preprocess', 'postprocess' ]
		})

		const datasets = response.datasets

		return datasets

	}catch(err){
		console.error(err)
	}
}

getMetadata

A method that returns a Promise by making a call to the /metadata endpoint. It can take in an argument containing one of the datasets from the available dataset list.

const { getMetadata } = useTerracotta()

const handleMetadata = async () => {
	try {
		const metadata = await getMetadata({ ...dataset })

		return metadata

	} catch(err) {
		console.error(err)
	}
}

Deck.gl hooks

This package includes a few helper functions that can be used during the implementation of Terracotta and Deck.gl. This readme file should give you an overview of what hooks are available and how to use them.

useTerracottaLayer

The hook applies the same concept as the useRasterLayer, and at the same time it wraps up some of the logic around rendering the terracotta raster/s.

The layer can take in more than one dataset and show it on the map, especially when there are multiple tiles to be displayed for the same area of interest.

Usage

import { useTerracottaLayer } from "@dhi-gras/terracotta-react";

const datasets = [
	{
		"key1": "",
		"key2": false,
		"key3": 0
	},
	{
		"key1": "",
		"key2": true,
		"key3": 0
	}
]

const terracotta = useTerracottaLayer({
	id: 'post-classification-terracotta-layer',
	url: https://www.terracotta-deployment.com,
	datasets: [ ...datasets ],
	type: "singleband",
	queryString: "colormap=binary&stretch_range=[0,1]" // Depends on the type of data
	...otherTileLayerProps
})

Props

List of specific props related mainly to Terracotta. The rest of the props passed are the same as for the TileLayer and will be applied to the TileLayer.

url*

The terracotta instance url without the ending "/".

id*

The unique identifier for the given layer.

datasets

This represents the dataset/s that are to be displayed on the map as TileLayers.

type

The type is related to the type of data that the user would like to render. The options available are 'singleband' and 'rgb'. You can read more about the differences in the official documentation.

queryString

The queryString is used to specify the ranges you would like to see for the Red, Green or Blue band through the r_range, b_range, g_range query parameters.

You can also specify the colormap and the stretch_range in case of 'singleband' or to specify the colors for the categorical data.

useRasterLayer

The package exports a generic layer useRasterLayer that can be used in conjunction with any type of XYZ server. The layer takes in the same properties as For readming more about it, you can visit the TileLayer documentation.

Usage

import { useRasterLayer } from "@dhi-gras/terracotta-react";

const rasterLayer = useRasterLayer({
	id: 'post-classification-terracotta-layer',
	data: https://www.terracotta-deployment.com/key1/key2/{z}/{x}/{y}.png,
	...otherTileLayerProps
})

Terracotta specific query parameters

In order to render the right colormaps for your data, some specific combination of query parameters must be set.

RGB layers

For rendering RGB layers, we have to specify the following:

• The bands respective to red, green and blue colors.
• The ranges respective to each band.

const rRangeValue = encodeURI([0,1000])
const gRangeValue = encodeURI([0,1000])
const bRangeValue = encodeURI([0,1000])

`.../{z}/{x}/{y}.png?r=B04&g=B03&b=B02&r_range=${rRangeValue}&g_range=${gRangeValue}&b_range=${bRangeValue}`

Singleband layers

For rendering singleband layers, we have the following use-cases

Cateogorical data

For categorical data we must specify:

• The explicit colormap
• The explicit_color_map values

const categoricalColors = encodeURI({ "1": "B9D400", "2": "001BCB" })

`.../{z}/{x}/{y}.png?colormap=explicit&explicit_color_map=${categoricalColors}`

Continuous data

For continuous data we must specify:

• The desired colormap from the list of available colormaps.
• The stretch_range for the range of values to be displayed.

const stretchContinuousColor = encodeURI([0,1])
const continuousColor = 'autumn'

`.../{z}/{x}/{y}.png?colormap=autumn&stretch_range=${stretchContinuousColor}`