torque/doc/torque_api.md

Torque API

L.TorqueLayer(options)

A layer to be added to a Leaflet map. It works as a regular tiled layer within the Leaflet tile pane, but instead of containing <img> elements, it's composed of a single <canvas> where all markers are drawn.

var torqueLayer = new L.TorqueLayer({
  user: 'viz2',
  table: 'ow',
  cartocss: '<cartocss here>'
});

map.addLayer(torqueLayer);

Options

Name	Description
cartocss	A string object, the CartoCSS style for the map. Default value is null
loop	A boolean object that defines the animation loop. Default value is true. If false, the animation is paused when it reaches the last frame
resolution	Spatial resolution in pixels. A resolution of 1 means no spatial aggregation of the data. Its value must be a power of 2
steps	Number of steps that the animation is divided into
animationDuration	Duration, in seconds, of the animation
zIndex	Z-Index CSS property of the layer
attribution	Attribution to be added in the bottom right of the map
maxZoom	Maximum zoom for the layer.
tileSize	Size, in pixels of the tiles

Using a CartoDB table directly

Name	Description
user	A string object, your CartoDB account name. Default value is null
table	A string object, the CartoDB table name where data is found (also known as a dataset.) Default value is null

Using a custom SQL query

Name	Description
query	A string object, the SQL query to be performed to fetch the data. Default value is null. You must use this param or table, but not at the same time

Tip: For a Torque category layer that is created dynamically with cartodb.createLayer, the SQL query must explicitly include how to build the torque_category column. You must include both the sql and table_name parameters. See this createLayer with torque category layer example.

Providing a TileJSON file

Name	Description
tileJSON	A URL pointing to a valid TileJSON file from which to get the Torque tile templates

Time Methods

Method	Options	Returns	Description
setStep(step)	time numeric	this	the value must be between 0 and the total number of steps in the animation
play()		this	starts the animation
stop()		this	stops the animation and set time to step 0
pause()		this	stops the animation but keep the current time (play enables the animation again)
toggle()		this	toggles (pause/play) the animation
getStep()		current animation step (integer)	gets the current animation step. A step is considered an animation frame
getTime()		current animation time (Date)	gets the real animation time
isRunning()		true/false	describes whether the Torque layer is playing or is stopped

Note: Torque.js interprets the beginning and ending date/time from your "Time Column" as one block, then divides that up into Steps, depending on the number you set. It does not necessarily draw one frame for each row.

Layer Control Methods

Method	Options	Returns	Description
hide()	none	this	hides the Torque layer
show()	none	this	shows the Torque layer

Style Methods

Method	Options	Returns	Description
setCartoCSS(cartocss)	cartocss string	this	style the map rendering using client-side CartoCSS (not available with Named maps)

Torque supports a limited subset of CartoCSS rules defined in the torque-reference. To see the full list of supported rules, read the Torque CartoCSS documentation. value and zoom variables can be used. value is the value of aggregation. zoom is the current zoom being rendered.

TorqueLayer currently expects marker styling.

Example

This is how a minimal example of a stylesheet for a Torque visualisation would look like.

Map {
  -torque-time-attribute: "date";
  -torque-aggregation-function: "count(cartodb_id)";
  -torque-frame-count: 760;
  -torque-animation-duration: 15;
  -torque-resolution: 2;
}
#layer {
  marker-width: 3;
  marker-fill-opacity: 0.8;
  marker-fill: #FEE391; 
}
#layer[value = 4] { // Use of the value variable, generated by the function specified in -torque-aggregation-function
  marker-fill: #FABADA; 
}
#layer[zoom = 12] { // Use of the zoom variable
  marker-width: 10;
}

Data Methods

Method	Options	Returns	Description
setSQL(sql statement)	SQL string	this	Change the SQL on the data table (not available with named maps)
error(callback)	callback function with a list of errors as argument	this	specifies a callback function to run if there are query errors

Example

SQL Example to limit the data used in the Torque map.

torqueLayer.setSQL("SELECT * FROM table LIMIT 100");

Events

Events in Torque follow the format:

torqueLayer.on('event-type', function([callback_obj]) {
  // do something
});

Events	Callback Object	Description
change:steps	current step	When a map changes steps, this event is triggered
change:time	current time, step number	When a map changes time, this event is triggered
play	none	Triggered when the Torque layer is played
pause	none	Triggered when the Torque layer is paused
stop	none	Triggered when the Torque layer is stopped
load	none	Triggered when the Torque layer is loaded

Example

An event example to print the current step to the console log.

torqueLayer.on('change:steps', function(step) {
  // do something with step
  console.log('Current step is ' + step);
});

Google Maps Layers

GMapsTorqueLayer(options)

This class does exactly the same as L.TorqueLayer but using Google Maps instead. The main difference is that this class is not a layer but is an overlay, so in order to add it to the a map use, layer.setMap instead of overlayMapTypes. See the Overlay View reference in Google Maps API doc.

Options

Name	Description
map	A google.maps.Map instance