inkmap: A JavaScript repository from County of Simcoe GIS

inkmap, a library for generating high resolution maps in the browser

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.

field	type	description
`layers`	`Layer[]`	Array of `Layer` objects that will be rendered in the map; last layers will be rendered on top of first layers.
`size`	`[number, number]` or `[number, number, string]`	Width and height in pixels, or in the specified unit in 3rd place; valid units are `px`, `mm`, `cm`, `m` and `in`.
`center`	`[number, number]`	Longitude and latitude of the map center.
`dpi`	`number`	Dot-per-inch, usually 96 for a computer screen and 300 for a detailed print.
`scale`	`number`	Scale denominator.
`scaleBar`	`boolean \| ScaleBarSpec`	Indicates whether scalebar should be printed (`true`). Also allows to pass options object: `{"position": "bottom-left", "units": "metric" }` (default values). Possible values are: `position`: `"bottom-left" \| "bottom-right"` `units`: `"degrees" \| "imperial" \| "metric" \| "nautical" \| "us"` (same as `ol.control.ScaleLine`)
`northArrow`	`boolean \| string`	North arrow position; either `'top-left'`, `'bottom-left'`, `'bottom-right'` or `'top-right'`; `true` defaults to `'top-right'`; absent or `false` means not to print the north arrow.
`projection`	`string`	Projection name. If starting with `EPSG:`, and other than `EPSG:3857` or `EPSG:4326`, definition will be downloaded on [https://epsg.io/].
`projectionDefinitions`	`[projectionDefinition]`	Optional. Registers new projections from the definitions.
`attributions`	`boolean \| string`	Position of the attributions to be printed on the map; either `'top-left'`, `'bottom-left'`, `'bottom-right'` or `'top-right'`; if not defined, attributions will not be printed.

`Layer` type

A Layer object describes a layer in the printed map.

field	type	description
`type`	`string`	Either `XYZ`, `WMTS`, `WMS`, `WFS` or `GeoJSON`.
`url`	`string`	URL or URL template for the layer; for XYZ layers, a URL can contain the following tokens: `{a-d}` for randomly choosing a letter, `{x}`, `{y}` and `{z}`.
`opacity`	`number`	Opacity, from 0 (hidden) to 1 (visible).
`attribution`	`string`	Attribution for the data present in the layer.
`legend`	`boolean`	Include this layer in the map legend. Defaults is false.

`WMS layer` type

Additional options for WMS layer type.

field	type	description
`layer`	`string`	Layer name.
`version`	`string`	Version of WMS protocol used: `1.1.1` or `1.3.0` (default).
`tiled`	`boolean`	Indicates whether the WMS layer should be requested as tiles. Defaults to `false`.
`customParams`	`Object`	Additional params used in all GetMap requests (optional).

`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.

field	type	description
`requestEncoding`	`string`	Request encoding: `KVP`, `REST`.
`format`	`string`	Image format. Only used when `requestEncoding` is `'KVP'`. eg `image/png`.
`layer`	`string`	Layer name as advertised in the WMTS capabilities.
`style`	`number`	Style name as advertised in the WMTS capabilities.
`projection`	`string`	Projection.
`matrixSet`	`string`	Matrix set.
`tileGrid`	`TileGrid`	TileGrid object, see https://openlayers.org/en/latest/apidoc/module-ol_tilegrid_TileGrid-TileGrid.html for options

`WFS layer` type

Additional options for WFS layer type.

field	type	description
`layer`	`string`	Layer name.
`version`	`string`	Version of WFS protocol used: `1.0.0`, `1.1.0` (default) or `2.0.0`.
`format`	`string`	Format used when querying WFS, `gml` (default) or `geojson`. inkmap determines the GML parser based on the WFS version used.
`style`	`object`	JSON object in geostyler notation, defining the layer style.

`GeoJSON layer` type

Additional options for GeoJSON layer type.

field	type	description
`geojson`	`object`	Feature collection in GeoJSON format; coordinates are expected to be in the print job reference system.
`style`	`object`	JSON object in geostyler notation, defining the layer style.

`projectionDefinition` type

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

field	type	description
`name`	`string`	Name of the projection, written as `prefix`:`code`.
`bbox`	`[number, number, number, number]`	Extent of the projection, written as `[maxlat, minlon, minlat, maxlon]`.
`proj4`	`string`	Proj4 definition string.

`PrintStatus` type

A PrintStatus object describes the status of a print job.

field	type	description
`id`	`number`	Job id.
`progress`	`number`	Job progress, from 0 to 1.
`status`	`string`	Either `'pending'`, `'ongoing'`, `'finished'` or `'canceled'`.
`imageBlob`	`Blob	null`
`spec`	`PrintSpec`	The spec used for this job.
`sourceLoadErrors`	`SourceLoadError[]`	Array of `SourceLoadError` objects.

`SourceLoadError` type

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

field	type	description
`url`	`string`	URL of the ol.source that encountered at least one 'tileloaderror' or 'imageloaderror'.

`PrintableImage` class

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

method	return type	description
`getImage()`	`HTMLImageElement` or `HTMLCanvasElement`	Returns the native image to be drawn or printed.
`getRealWorldDimensions(units: string)`	`[number, number]`	Returns the real world dimensions of the image for a given unit (e.g. `mm`).
`getDpi()`	`number`	Returns the image DPI.

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

county-of-simcoe-gis/inkmap

Live demo here!

Introduction

Usage

Basic

Advanced

Enabling the service worker

API

print(jsonSpec: PrintSpec): Promise<Blob>

queuePrint(jsonSpec: PrintSpec): Promise<number>

getJobStatus(id: number): Observable<PrintStatus>

cancelJob(id: number): void

getJobsStatus(): Observable<PrintStatus[]>

registerProjection(definition: ProjectionDefinition): void

getAttributionsText(spec: PrintSpec): string

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

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

createLegend(jsonSpec: PrintSpec): Promise<Blob>

PrintSpec type

Layer type

WMS layer type

WMTS layer type

WFS layer type

GeoJSON layer type

projectionDefinition type

PrintStatus type

SourceLoadError type

PrintableImage class