OpenLayers.Tile.UTFGrid

Instances of OpenLayers.Tile.UTFGrid are used to manage UTFGrids. This is an unusual tile type in that it doesn’t have a rendered image; only a ‘hit grid’ that can be used to look up feature attributes.

See the OpenLayers.Tile.UTFGrid constructor for details on constructing a new instance.

Inherits from

OpenLayers.Tile

Summary

OpenLayers.Tile.UTFGrid	Instances of OpenLayers.Tile.UTFGrid are used to manage UTFGrids.
Properties
url	{String} The URL of the UTFGrid file being requested.
utfgridResolution	{Number} Ratio of the pixel width to the width of a UTFGrid data point.
json	{Object} Stores the parsed JSON tile data structure.
format	{OpenLayers.Format.JSON} Parser instance used to parse JSON for cross browser support.
Constructor
OpenLayers.Tile.UTFGrid	Constructor for a new OpenLayers.Tile.UTFGrid instance.
Functions
destroy	Clean up.
draw	Check that a tile should be drawn, and draw it.
abortLoading	Cancel a pending request.
getFeatureInfo	Get feature information associated with a pixel offset.
getFeatureId	Get the identifier for the feature associated with a pixel offset.
indexFromCharCode	Given a character code for one of the UTFGrid “grid” characters, resolve the integer index for the feature id in the UTFGrid “keys” array.
parseData	Parse the JSON from a request
clear	Delete data stored with this tile.

Properties

url

{String} The URL of the UTFGrid file being requested. Provided by the getURL method.

utfgridResolution

{Number} Ratio of the pixel width to the width of a UTFGrid data point. If an entry in the grid represents a 4x4 block of pixels, the utfgridResolution would be 4. Default is 2.

json

{Object} Stores the parsed JSON tile data structure.

format

{OpenLayers.Format.JSON} Parser instance used to parse JSON for cross browser support. The native JSON.parse method will be used where available (all except IE<8).

Constructor

OpenLayers.Tile.UTFGrid

Constructor for a new OpenLayers.Tile.UTFGrid instance.

Parameters

layer	{OpenLayers.Layer} layer that the tile will go in.
position	{OpenLayers.Pixel}
bounds	{OpenLayers.Bounds}
url	{String} Deprecated. Remove me in 3.0.
size	{OpenLayers.Size}
options	{Object}

Functions

destroy

destroy: function()

Clean up.

draw

draw: function()

Check that a tile should be drawn, and draw it. In the case of UTFGrids, “drawing” it means fetching and parsing the json.

Returns

{Boolean} Was a tile drawn?

abortLoading

abortLoading: function()

Cancel a pending request.

getFeatureInfo

getFeatureInfo: function( i,
j )

Get feature information associated with a pixel offset. If the pixel offset corresponds to a feature, the returned object will have id and data properties. Otherwise, null will be returned.

Parameters

i	{Number} X-axis pixel offset (from top left of tile)
j	{Number} Y-axis pixel offset (from top left of tile)

Returns

{Object} Object with feature id and data properties corresponding to the given pixel offset.

getFeatureId

getFeatureId: function( i,
j )

Get the identifier for the feature associated with a pixel offset.

Parameters

i	{Number} X-axis pixel offset (from top left of tile)
j	{Number} Y-axis pixel offset (from top left of tile)

Returns

{Object} The feature identifier corresponding to the given pixel offset. Returns null if pixel doesn’t correspond to a feature.

indexFromCharCode

indexFromCharCode: function( charCode )

Given a character code for one of the UTFGrid “grid” characters, resolve the integer index for the feature id in the UTFGrid “keys” array.

Parameters

charCode

{Integer}

Returns

{Integer} Index for the feature id from the keys array.

parseData

parseData: function( str )

Parse the JSON from a request

Parameters

str	{String} UTFGrid as a JSON string.

Returns

{Object} parsed javascript data

clear

clear: function()

Delete data stored with this tile.