Welcoming JavaScript library AMap
into the world of R.
AMap is an advanced mapping library made in China and widely used there.
It features 2D/3D animation, supports a multitude of layers and markers,
data import, flyover playback, etc.
Library amapro let you
control AMap from R and Shiny. It uses AMap’s native commands/parameters
wrapped in just a few commands.
AMap’s documentation is in Chinese and most links here make reference to it. If you happen not to know Chinese, it is convenient to set your browser to auto-translate. This will help a little or a lot depending on the website/page structure. One can also copy/paste text to Google translate.
Install amapro from Github with
remotes::install_github("helgasoft/amapro")
CRAN version also available but usually outdated.
Run with the following commands
library(amapro); am.init()
A pop-up dialog will ask
for an API key (shows once, will not be repeated).
API key is obtained through registration, expecting
you to provide a Chinese phone number for SMS verification.
How to
get an API key if you reside out of China?
Interactive, hands-on showcase of many library features. Activate
with the following command:
library(amapro); demo(am.shiny)
amapro is based on version 2.0 of AMap (JSAPI v2.0). “API” auto-translates as “Reference book” in web menus.
The base library with optional plugins. Most important links are
Controlling map and elements is done by sending AMap commands to
them. Commands can be chained with the pipe operator |> or %>% and
are executed sequentially in the order received.
Example:
am.cmd('setAngle', 'carIcon', -90)
amapro
uses native AMap commands and introduces these
additional:
am.cmd('set', 'VectorLayer', name='e$layer1')am.cmd('set', 'e$marker1', position= c(116.478, 39.998))am.cmd('addTo', 'e$layer1', 'e$marker1')am.cmd('var', 'e$myOpacity', 0.8)am.cmd('code', 'alert("I am JS");')AMap commands starting with get return data from the
map or related objects.
Put the data in a Shiny input variable by
setting its name in parameter r.
Example:
am.cmd('getCenter', 'map', r='inShiny1')
Above command
will update input$inShiny1 with the Lng/Lat coordinates of the
map center.
Events could be defined for map and elements. All types of instances
use on/off methods to bind and remove events.
Events are set in attribute on(or off)
as a list of lists. Each event is a separate list with event name in
e, a JS function f and optionally a
query q.
Example:
am.init(center= c(116.475, 39.997), zoom= 17,
on= list(list(e= 'complete',
f= "function() {alert('loaded!');}")) )on/off events without name are ignored, except for the map
itself (as above example).
JavaScript function
Shiny.setInputValue() can be used to send data back to
Shiny.
all named objects created in JS are global variables (window.name). Good practice is to use a name prefix (m$) to avoid overwriting accidentally external variables.
API attributes could be set to a JS function instead of a value. Function is defined as a string starting with word “function”.
usually WMS/WMTS tiles come from external servers and may present a CORS problem - browser refusal to load. One can install a small extension in Chrome or Firefox to fix this problem manually inside the browser.
AMap has several predefined Map styles. Could be set in map options with mapStyle.
amapro silent errors are collected in the browser Console. Press key F12 to open the dev.environment, then open tab “Console” to view them.
Chrome/Firefox extensions may interfere with map presentation (like ‘uBlock’)