@camptocamp/inkmap v1.4.0

Live demo here!

Introduction

inkmap is based on OpenLayers and will generate maps in PNG format based on a given JSON specification.

inkmap can handle long-running jobs (e.g. A0 format in 300 dpi) and provides an API for following a job progress. It uses a service worker in the background provided the user browser supports OffscreenCanvas, and falls back (almost) seamlessly to the main thread if not.

Please note that the first version of inkmap has been entirely funded and supported by the French Ministry of Ecology as part of their Descartes web mapping toolkit, hosted here: https://adullact.net/projects/descartes/

Usage

Basic

To include the library in your project:

$ npm install --save @camptocamp/inkmap

Then import the different methods from the inkmap package:

import { print, downloadBlob } from '@camptocamp/inkmap';

print({
  layers: [ ... ],
  projection: 'EPSG:4326',
  ...
}).then(downloadBlob);

Advanced

inkmap offers advanced job monitoring through the use of Observables provided by the rxjs library.

Observables are different from Promises in that they can emit multiple values instead of just one, and are a very good fit for progress reporting.

To use an Observable, simply call its subscribe() method with a function as argument. The function will be called anytime a new value is emitted, like so:

import { getJobStatus } from '@camptocamp/inkmap';

...

getJobStatus(jobId).subscribe((jobStatus) => {
  // do something with the status
});

Note that for long-lived Observables (i.e. Observables that never completes) it is important to call unsubscribe() when the emitted values are not needed anymore. Open subscriptions to Observables might create memory leaks.

Enabling the service worker

inkmap can and will use a dedicated service worker for running print jobs if given the chance. This offers the following advantages:

• Jobs run in a separate thread, meaning the user navigation will not be impacted at all by any CPU-intensive task
• The service worker isn't tied to a window or tab, so jobs will continue running when the tab is closed (and even when the browser is closed, depending on the platform)
• Push notifications might be sent to the user when a print job complete (not implemented yet)

To enable this, the inkmap-worker.js file located in the dist folder must be published on the same path as the application using inkmap.

The worker file can be published either using a symbolic link or by actually copying the file, for example in the application build pipeline.

If using Webpack to build the application, a solution is to use the CopyWebpackPlugin:

module.exports = {
  ...
  plugins: [
     new CopyWebpackPlugin([
       {
         from: 'node_modules/@camptocamp/inkmap/dist/inkmap-worker.js',
         to: 'dist'
       },
     ]),
  ],
  ...
}

API

Important note: all API functions are named exports from the inkmap package.

print(jsonSpec: PrintSpec): Promise<Blob>

Takes in a PrintSpec object and returns a Promise which resolves to a Blob containing the final image.

queuePrint(jsonSpec: PrintSpec): Promise<number>

Takes in a PrintSpec object and returns a Promise which resolves to a job id (number) immediately.

getJobStatus(id: number): Observable<PrintStatus>

Takes in a job id and returns an Observable which will regularly emit PrintStatus objects, and complete when the final image was generated.

cancelJob(id: number): void

Takes in a job id, cancel the job and cease all requests immediately.

getJobsStatus(): Observable<PrintStatus[]>

Returns a long-running observable which emits an array of print job status. Once a job is finished it will appear once in the array and then will not be part of subsequent emissions.

Note: This observable will never complete. Don't forget to unsubscribe!

registerProjection(definition: ProjectionDefinition): void

Takes in a projection definition and registers it with proj4.

getAttributionsText(spec: PrintSpec): string

Returns the full attributions text of the spec.

getNorthArrow(spec: PrintSpec, sizeHint?: [number, string]): PrintableImage

Returns a PrintableImage containing the north arrow for the given spec. The image will be square and have the same DPI as the spec. A sizeHint (e.g. [3, 'cm']) can be provided to request a larger or smaller arrow. Supported size units are the same as in the PrintSpec type.

getScaleBar(spec: PrintSpec, minimumWidth?: [number, string]): PrintableImage

Returns a PrintableImage containing the scale bar for the given spec. The image will have the same DPI as the spec. A minimumWidth (e.g. [80, 'mm']) can be provided to request a smaller or larger scale bar. Supported size units are the same as in the PrintSpec type.

Note that for this scale bar to be relevant in a printed document, its real-world size has to be respected.

createLegend(jsonSpec: PrintSpec): Promise<Blob>

Takes in a PrintSpec object and returns a Promise which resolves to a Blob containing the final legend image.

PrintSpec type

A PrintSpec object describes the content and aspect of the map to be printed.

Layer type

A Layer object describes a layer in the printed map.

WMS layer type

Additional options for WMS layer type.

WMTS layer type

Additional options for WMTS layer to define the layer source. See https://openlayers.org/en/latest/apidoc/module-ol_source_WMTS-WMTS.html for the full list of options. The following table introduces the common options to use.

WFS layer type

Additional options for WFS layer type.

GeoJSON layer type

Additional options for GeoJSON layer type.

projectionDefinition type

A projectionDefinition object describes a projection to be registered in proj4.

PrintStatus type

A PrintStatus object describes the status of a print job.

SourceLoadError type

A SourceLoadError object contains the URL for tile sources which produced errors while loading data.

PrintableImage class

A PrintableImage is essentially a wrapper around a native image or canvas, with added information about its real world size.

Architecture

Under the hood, inkmap will attempt to install a service worker on the page it is called. The service worker will then be in charge of loading all the map images and data, composing them together and giving them back to the application code.

Contributing

See CONTRIBUTING.

License

CeCILL-C