README
geo-viewport
This repository is a fork of
mapbox/geo-viewport
, but for CGCS200 projection.
Turns bounding boxes / extents into centerpoint & zoom combos for static maps.
Works in node.js and browsers, via browserify or a script tag.
Install
npm install --save @cgcs2000/geo-viewport
Or use a plugin:
<script src='//api.tiles.mapbox.com/mapbox.js/plugins/geo-viewport/v0.2.1/geo-viewport.js'></script>
The script-tag include exports an object called geoViewport
,
with methods bounds
and viewport
documented below.
Example
Live example with Mapbox Static Map API
With Node
var geoViewport = require('@cgcs2000/geo-viewport');
geoViewport.viewport([
5.668343999999995,
45.111511000000014,
5.852471999999996,
45.26800200000002
], [640, 480])
// yields
// {
// center: [
// 5.7604079999999955,
// 45.189756500000016
// ],
// zoom: 11
// }
In a browser:
<script src='//api.tiles.mapbox.com/mapbox.js/plugins/geo-viewport/v0.1.1/geo-viewport.js'></script>
<script>
var bounds = geoViewport.viewport([
5.668343999999995,
45.111511000000014,
5.852471999999996,
45.26800200000002
], [640, 480]);
var center = geoViewport.bounds(
[-75.03,
35.25],
14,
[600, 400]);
console.log(bounds);
console.log(center);
</script>
api
viewport(bounds, dimensions, minzoom, maxzoom, tileSize, allowFloat)
Given a WSEN
array of bounds and a [x, y]
array of pixel dimensions, return a { center: [lon, lat], zoom: zoom }
viewport. Use allowFloat
to retain float values in the output.
Example:
// first argument is the bounds, and the image is 640x480
geoViewport.viewport([
5.6683, 45.111, 5.8524, 45.268
], [640, 480])
bounds(viewport, zoom, dimensions, tileSize)
Given a centerpoint as [lon, lat]
or { lon, lat }
, a zoom,
and dimensions as [x, y]
, return a bounding box.
Example:
geoViewport.bounds([-75.03, 35.25], 14, [600, 400])
tile sizes
Be aware that these calculations are sensitive to tile size. The default size assumed by this library is 256x256px; however, Mapbox Vector Tiles are 512x512px.
For example, to calculating a bounding box for a classic raster-based 256x256 tile:
geoViewport.bounds([-75.03, 35.25], 14, [600, 400], 256)
// since 256 is default, you can omit the tileSize param
geoViewport.bounds([-75.03, 35.25], 14, [600, 400])
To calculate a bounding box for a Mapbox vector tile source, such as an image from the Mapbox Static Image API:
geoViewport.bounds([-75.03, 35.25], 14, [600, 400], 512)
There's a handy blog post discussing the issue here.