BaseLayerViewGL2D | API Reference | ArcGIS Maps SDK for JavaScript 4.31

Represents the LayerView of a Layer after it has been added to a Map with a MapView. In contrast to the related class BaseLayerView2D, this one exposes WebGL rendering capabilities.

Important notes

This interface is experimental. Please read the following information carefully before using it in a product.

Due to the nature of WebGL it is not possible to fully sandbox user-supplied code, and its malfunctions can affect the performance, visual quality and even stability of the entire MapView. For this reason, Esri does not provide any support for issues related to WebGL rendering in custom rendering code, or for issues that arise in MapView rendering while using custom rendering code.

This class may be extended to create a custom LayerView for a Layer. A LayerView is created on demand by the MapView when a layer is added the to list of layers of its map.

The subclass can implement multiple functions of the LayerView lifecycle.

First, the attach() method is called when the LayerView is about to start drawing the layer's content; it is usually responsible for resource allocation.
Then during the life of the LayerView the render() method is called once per frame; it must complete drawing before returning.
Finally the detach() method is called after the layer is removed from the map; it releases all allocated resources and stops on-going requests.

Each of these functions has access to the MapView's WebGL context through the instance property this.context. The developer must provide own shaders, meshes and textures, and is responsible for setting the required GL states on the context.

As a convenience for the developer, starting with version 4.14 of the API, BaseLayerViewGL2D includes tessellation helper methods; the developer can supply Point, Multipoint, Polyline, Extent, or Polygon geometries and have them converted to abstract descriptions of triangle meshes that can be easily fed to the GPU as vertex and index buffers. The SDK sample explains in detail how to use the tessellation helpers and how to write compatible shaders.

See also

Example

let CustomLayerView2D = BaseLayerViewGL2D.createSubclass({
   render(renderParameters) {
     const gl = this.context;

     ...
   }

   attach() {
     const gl = this.context;

     ...
   }

   detach() {
     const gl = this.context;

     ...
   }
 });

 let CustomTileLayer = Layer.createSubclass({
   tileInfo: TileInfo.create({ spatialReference: { wkid: 3857 }}),

   createLayerView(view) {
     if (view.type === "2d") {
       return new CustomLayerView2D({
         view: view,
         layer: this
       });
     }
   }
 });

Constructors

BaseLayerViewGL2D Constructor new BaseLayerViewGL2D(properties)

Parameter

properties Object

optional

See the properties for a list of all the properties that may be passed into the constructor.

Property Overview

Any properties can be set, retrieved or listened to. See the Watch for changes topic.

Show inherited properties

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Type	Summary	Class
WebGL2RenderingContext	The WebGL rendering context associated to this layer view.	BaseLayerViewGL2D
String	The name of the class.	Accessor
Layer	References the layer this LayerView represents.	BaseLayerViewGL2D
Boolean	Indicates if the spatialReference of the MapView is supported by the layer view.	LayerView
Boolean	Value is `true` if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).	LayerView
Tile []	The array of BaseLayerViewGL2D objects computed to cover the MapView's visible area.	BaseLayerViewGL2D
Boolean	Indicates if the layer view is making any updates that will impact what is displayed on the map.	LayerView
MapView	References the MapView this LayerView belongs to.	BaseLayerViewGL2D
Boolean	When `true`, the layer is visible in the view.	LayerView
Boolean	When `true`, the layer is visible in the view at the current scale.	LayerView
Boolean	When `true`, the layer is visible in the view's timeExtent.	LayerView

Property Details

context Property context WebGL2RenderingContext

The WebGL rendering context associated to this layer view.

declaredClass Inherited Property declaredClass Stringreadonly Inherited from Accessor

The name of the class. The declared class name is formatted as esri.folder.className.

layer Property layer Layer

References the layer this LayerView represents.

spatialReferenceSupported Inherited Property spatialReferenceSupported Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.23 LayerView since 4.0, spatialReferenceSupported added at 4.23.

Indicates if the spatialReference of the MapView is supported by the layer view. When false layer view will be suspended.

See also

suspended

suspended Inherited Property suspended Booleanreadonly Inherited from LayerView

Value is true if the layer is suspended (i.e., layer will not redraw or update itself when the extent changes).

See also

spatialReferenceSupported

tiles Property tiles Tile[]

The array of BaseLayerViewGL2D objects computed to cover the MapView's visible area. This array is updated when the view is animating or the user is interacting with it. Then if tiles have been added or removed, tilesChanged() is called.

See also

tilesChanged()

updating Inherited Property updating Booleanreadonly Inherited from LayerView

Indicates if the layer view is making any updates that will impact what is displayed on the map. For example, this value is true when renderer, definitionExpression, filter or effect is changed or if the layer view is in the process of the fetching data.

Watch dataUpdating property instead to only know when the data has been updated (e.g. to run statistics query on all feature available in the layer view).

Default Value:false

Example

// Check for the first time layerView.updating becomes false. Then query for
// features that are visible within the view associated with the layer view.
await reactiveUtils.whenOnce(() => !layerView.updating);
const query = layerView.createQuery();
query.geometry = layerView.view.extent;
const result = layerView.queryFeatures(query);

view Property view MapView

References the MapView this LayerView belongs to.

visible Inherited Property visible Boolean Inherited from LayerView

When true, the layer is visible in the view. Value of this property is inherited from the layer.visible unless the developer overrides it. The layerView.visible will take precedence over layer.visible if both properties are set.

Default Value:true

visibleAtCurrentScale Inherited Property visibleAtCurrentScale Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.30 LayerView since 4.0, visibleAtCurrentScale added at 4.30.

When true, the layer is visible in the view at the current scale. This applies to layers that have minScale and maxScale properties set.

Known Limitations

This property is not supported in 3D SceneView tiled layers.

Default Value:true

See also

visibleAtCurrentTimeExtent
suspended

visibleAtCurrentTimeExtent Inherited Property visibleAtCurrentTimeExtent Booleanreadonly Inherited from LayerView Since: ArcGIS Maps SDK for JavaScript 4.30 LayerView since 4.0, visibleAtCurrentTimeExtent added at 4.30.

When true, the layer is visible in the view's timeExtent. This applies to layers that have a visibilityTimeExtent.

Default Value:true

See also

visibleAtCurrentScale
suspended

Method Overview

Show inherited methods

Hide inherited methods

Return Type	Summary	Class
	Adds one or more handles which are to be tied to the lifecycle of the object.	Accessor
	Method called after the LayerView is created and right before it starts drawing the layer's content.	BaseLayerViewGL2D
	Bind the designated rendering output surface and restore the correct viewport.	BaseLayerViewGL2D
	Method called after the layer is removed and the LayerView is about to be removed.	BaseLayerViewGL2D
RenderTarget	Get the designated rendering output surface and corresponding viewport configuration.	BaseLayerViewGL2D
Boolean	Returns true if a named group of handles exist.	Accessor
Promise<Graphic []>	Method to implement that is responsible for providing objects hit at the specified screen coordinates.	BaseLayerViewGL2D
Boolean	`isFulfilled()` may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected).	LayerView
Boolean	`isRejected()` may be used to verify if creating an instance of the class is rejected.	LayerView
Boolean	`isResolved()` may be used to verify if creating an instance of the class is resolved.	LayerView
	Removes a group of handles owned by the object.	Accessor
	The method to implement that is responsible of drawing the content of the layer.	BaseLayerViewGL2D
	The LayerView can call this method to ask the MapView to schedule a new rendering frame.	BaseLayerViewGL2D
Promise<TessellatedMesh>	Tessellate an Extent into a rectangle.	BaseLayerViewGL2D
Promise<TessellatedMesh>	Tessellate a Multipoint into quads (markers).	BaseLayerViewGL2D
Promise<TessellatedMesh>	Tessellate a Point into a quad (marker).	BaseLayerViewGL2D
Promise<TessellatedMesh>	Tessellate a Polygon into triangles.	BaseLayerViewGL2D
Promise<TessellatedMesh>	Tessellate a Polyline into triangles.	BaseLayerViewGL2D
	Method to implement, which notifies of tiles being added or removed for the current view state.	BaseLayerViewGL2D
Promise	`when()` may be leveraged once an instance of the class is created.	LayerView

Method Details

addHandles Inherited Method addHandles(handleOrHandles, groupKey) Inherited from Accessor Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, addHandles added at 4.25.

Adds one or more handles which are to be tied to the lifecycle of the object. The handles will be removed when the object is destroyed.

// Manually manage handles
const handle = reactiveUtils.when(
  () => !view.updating,
  () => {
    wkidSelect.disabled = false;
  },
  { once: true }
);

this.addHandles(handle);

// Destroy the object
this.destroy();

Parameters

handleOrHandles WatchHandle|WatchHandle []

Handles marked for removal once the object is destroyed.

groupKey *

optional

Key identifying the group to which the handles should be added. All the handles in the group can later be removed with Accessor.removeHandles(). If no key is provided the handles are added to a default group.

attach Method attach()

Method called after the LayerView is created and right before it starts drawing the layer's content. Typically this method is implemented to start watching property changes on the layer and to initialize WebGL objects such as shaders.

See also

detach()

Example

// Create a shader program and a property watcher
attach() {
  let gl = this.context;

  this._shaderProgram = gl.createProgram();
  ...

  this._propertyHandle = reactiveUtils.watch(
    () => this.layer.opacity,
    () => this.requestRender()
  );
}

bindRenderTarget Method bindRenderTarget()

Bind the designated rendering output surface and restore the correct viewport.

This method can be used after the WebGL state has been altered by a call to gl.bindFramebuffer() to restore the framebuffer that contains the final, composited frame, i.e. the one that is guaranteed to be bound right before control is handed over to render(). Note that this may or may not be the default framebuffer; MapView can use various surfaces for frame compositing and there is no guarantee that when render() is called, the bound framebuffer is the default one.

Together with the framebuffer, also a matching full-size viewport is restored.

Example

render() {
  let gl = this.context;

  ...

  // Bind a temporary offscreen surface
  gl.bindFramebuffer(gl.FRAMEBUFFER, this.myOffscreenSurface);

  ...

  // Render to the offscreen surface

  ...

  // Bind the original render surface so that the image stored
  // into the temporary one can be blitted/composited with the
  // actual frame data
  this.bindRenderTarget();

  ...

  // Your own frame composition logic

  ...
}

detach Method detach()

Method called after the layer is removed and the LayerView is about to be removed. Typically, this method is implemented to free resources like watchers and destroy WebGL objects such as shader programs.

See also

attach()

Example

// Remove the watchers and destroy the shader program created in attach()
detach() {
  this._propertyHandle.remove();
  this._propertyHandle = null;

  const gl = this.context;

  gl.deleteProgram(this._shaderProgram);
  this._shaderProgram = null;
}

getRenderTarget Method getRenderTarget(){RenderTarget}

Get the designated rendering output surface and corresponding viewport configuration.

The returned object is the same render target that is restored by a call to bindRenderTarget().

Returns

Type	Description
RenderTarget

hasHandles Inherited Method hasHandles(groupKey){Boolean} Inherited from Accessor Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, hasHandles added at 4.25.

Returns true if a named group of handles exist.

Parameter

groupKey *

optional

A group key.

Returns

Type	Description
Boolean	Returns `true` if a named group of handles exist.

Example

// Remove a named group of handles if they exist.
if (obj.hasHandles("watch-view-updates")) {
  obj.removeHandles("watch-view-updates");
}

hitTest Method hitTest(mapPoint, screenPoint){Promise<Graphic[]>}

Method to implement that is responsible for providing objects hit at the specified screen coordinates. This method is called internally by the MapView each time its hitTest() method is called.

Parameters

mapPoint Point

The point in map units.

screenPoint ScreenPoint

The point in screen coordinates.

Returns

Type	Description
Promise<Graphic []>	A Promise that resolves to an array of graphics.

isFulfilled Inherited Method isFulfilled(){Boolean} Inherited from LayerView

isFulfilled() may be used to verify if creating an instance of the class is fulfilled (either resolved or rejected). If it is fulfilled, true will be returned.

Returns

Type	Description
Boolean	Indicates whether creating an instance of the class has been fulfilled (either resolved or rejected).

isRejected Inherited Method isRejected(){Boolean} Inherited from LayerView

isRejected() may be used to verify if creating an instance of the class is rejected. If it is rejected, true will be returned.

Returns

Type	Description
Boolean	Indicates whether creating an instance of the class has been rejected.

isResolved Inherited Method isResolved(){Boolean} Inherited from LayerView

isResolved() may be used to verify if creating an instance of the class is resolved. If it is resolved, true will be returned.

Returns

Type	Description
Boolean	Indicates whether creating an instance of the class has been resolved.

removeHandles Inherited Method removeHandles(groupKey) Inherited from Accessor Since: ArcGIS Maps SDK for JavaScript 4.25 Accessor since 4.0, removeHandles added at 4.25.

Removes a group of handles owned by the object.

Parameter

groupKey *

optional

A group key or an array or collection of group keys to remove.

Example

obj.removeHandles(); // removes handles from default group

obj.removeHandles("handle-group");
obj.removeHandles("other-handle-group");

render Method render(renderParameters)

The method to implement that is responsible of drawing the content of the layer. This method is called every time the MapView's state changes, or if requestRender() has been called.

Parameters

Specification

renderParameters Object

Specification

context WebGL2RenderingContext

The WebGL or WebGL 2 context. Its concrete type depends on system configuration. Every time that render() is called, the API automatically resets WebGL to a conventional state which is almost the default one; the only two things that may be non-default are the bound framebuffer and the viewport, which is set to match the entire framebuffer. The body of render() must not change these settings.

stationary Boolean

The stationary state of the MapView.

state ViewState

The object that describes view state.

Example

// Example of a render implementation that draws using a custom shader program
render(renderParameters) {
  const gl = this.context;
  gl.bindBuffer(gl.ARRAY_BUFFER, this._vertexBuffer);
  gl.vertexAttribPointer(0, 2, gl.SHORT, false, 10, 0);
  gl.vertexAttribPointer(1, 3, gl.SHORT, true, 10, 4);
  gl.bindBuffer(gl.ARRAY_BUFFER, null);
  gl.enableVertexAttribArray(0);
  gl.enableVertexAttribArray(1);
  ...
  // Update uniforms as needed by calling gl.uniform...
  ...
  gl.useProgram(this._shaderProgram);
  gl.drawArrays(gl.TRIANGLES, 0, this._vertexCount);
  gl.disableVertexAttribArray(0);
  gl.disableVertexAttribArray(1);
  gl.useProgram(null);
}

requestRender Method requestRender()

The LayerView can call this method to ask the MapView to schedule a new rendering frame.

Example

// Call requestRender whenever the layer opacity has changed
attach() {
  this._propertyHandle = reactiveUtils.watch(
    () => this.layer.opacity,
    () => this.requestRender()
  );
}

tessellateExtent Method tessellateExtent(extent){Promise<TessellatedMesh>} Since: ArcGIS Maps SDK for JavaScript 4.14 BaseLayerViewGL2D since 4.11, tessellateExtent added at 4.14.

Tessellate an Extent into a rectangle.

Parameter

extent Extent

The input geometry.

Returns

Type	Description
Promise<TessellatedMesh>	A promise to a BaseLayerViewGL2D. The output mesh is composed of two triangles.

Example

this.tessellateExtent(g.geometry).then(function (mesh) {
   // do something with mesh
 });

tessellateMultipoint Method tessellateMultipoint(multipoint, footprint){Promise<TessellatedMesh>} Since: ArcGIS Maps SDK for JavaScript 4.14 BaseLayerViewGL2D since 4.11, tessellateMultipoint added at 4.14.

Tessellate a Multipoint into quads (markers).

Parameters

multipoint Multipoint

The input geometry. These are the geographic points where each marker will me anchored.

footprint Rect

The rectangle that describes the geometry of each marker. Coordinates x and y can be thought as being in screen-space, relative to the screen-space projection of the geographic point.

Returns

Type	Description
Promise<TessellatedMesh>	A promise to a BaseLayerViewGL2D. Each marker is represented by two triangles.

Example

this.tessellateMultipoint(g.geometry, {x: 0, : -12, width: 34, height: 10}).then(function (mesh) {
   // do something with mesh
 });

tessellatePoint Method tessellatePoint(point, footprint){Promise<TessellatedMesh>} Since: ArcGIS Maps SDK for JavaScript 4.14 BaseLayerViewGL2D since 4.11, tessellatePoint added at 4.14.

Tessellate a Point into a quad (marker).

Parameters

point Point

The input geometry. This is the geographic point where the marker will me anchored.

footprint Rect

The rectangle that describes the geometry of the marker. Coordinates x and y are the position of the upper-left corner of the marker, and can be thought as being in screen-space, relative to the screen-space projection of the geographic point; width and height are in pixels. See Rect for a visual explanation of marker geometry.

Returns

Type	Description
Promise<TessellatedMesh>	A promise to a TessellatedMesh. The output mesh is composed of two triangles.

Example

this.tessellatePoint(g.geometry, {x: 0, : -12, width: 34, height: 10}).then(function (mesh) {
   // do something with mesh
 });

tessellatePolygon Method tessellatePolygon(polygon){Promise<TessellatedMesh>} Since: ArcGIS Maps SDK for JavaScript 4.14 BaseLayerViewGL2D since 4.11, tessellatePolygon added at 4.14.

Tessellate a Polygon into triangles.

Parameter

polygon Polygon

The input geometry. The geometry must be simple; if the input geometry is not simple, you must first create a simplified version of it using geometryEngine, and pass the simplified geometry to tessellatePolygon.

Returns

Type	Description
Promise<TessellatedMesh>	A promise to a TessellatedMesh.

Example

this.tessellatePolygon(g.geometry).then(function (mesh) {
   // do something with mesh
 });

tessellatePolyline Method tessellatePolyline(polyline, width){Promise<TessellatedMesh>} Since: ArcGIS Maps SDK for JavaScript 4.14 BaseLayerViewGL2D since 4.11, tessellatePolyline added at 4.14.

Tessellate a Polyline into triangles.

Parameters

polyline Polyline

width Number

The width of the line; this will be used to scale xOffset and yOffset.

Returns

Type	Description
Promise<TessellatedMesh>	A promise to a TessellatedMesh.

Example

this.tessellatePolyline(g.geometry, 10).then(function (mesh) {
   // do something with mesh
 });

tilesChanged Method tilesChanged(added, removed)

Method to implement, which notifies of tiles being added or removed for the current view state. This function can be implemented to start and stop fetching new data, or allocate and dispose resources.

Parameters

added Tile []

The tile objects added for the current view viewport.

removed Tile []

The tile objects removed from the view viewport.

when Inherited Method when(callback, errback){Promise} Inherited from LayerView

when() may be leveraged once an instance of the class is created. This method takes two input parameters: a callback function and an errback function. The callback executes when the instance of the class loads. The errback executes if the instance of the class fails to load.

Parameters

callback Function

optional

The function to call when the promise resolves.

errback Function

optional

The function to execute when the promise fails.

Returns

Type	Description
Promise	Returns a new promise for the result of `callback` that may be used to chain additional functions.

Example

// Although this example uses MapView, any class instance that is a promise may use when() in the same way
let view = new MapView();
view.when(function(){
  // This function will execute once the promise is resolved
}, function(error){
  // This function will execute if the promise is rejected due to an error
});

Type Definitions

MeshVertex Type Definition MeshVertex Object

A vertex of a tessellated mesh.

There are five different tessellation algorithms, one for each supported geometry type. The attributes in a vertex can be used to populate vertex and index buffers that can be rendered using appropriate shaders. See the SDK sample for a possible way of doing this using a single universal shader program that can render any of the supported geometry types.

There are four attributes; the first three are 2D points, and the last one is a scalar value. In total a mesh vertex contains 7 numeric values.

Geographic position (x, y) The geographic point associated to that vertex. For Extent and Polygon is equivalent to the position of the vertex itself; for Point and Multipoint is the geographic position of the point, and the anchor that will be associated to the corresponding marker symbol; for Polyline it lies on the centerline. The geographic position is usually expressed in map units and a custom vertex shader will generally need to transform it to normalized device coordinates.

Offset vector (xOffset, yOffset) This is an offset that is generally expressed in units other than the view's ones, and drives the extrusion of the geographic position into lines and quads. For Extent and Polygon is zero; for Point and Multipoint it goes from the anchor to the four vertices of the quad on screen; for Polyline it goes from the centerline to a vertex on the polyline's edge. The offset vector is usually expressed in some other units than map and will not need to be transformed by the same transform used for the geographic position. A common convention is to express the offset in points or pixels and code the vertex shader accordingly.

tessellation-helpers-extrusion

Texture coordinates (uTexcoord, vTexcoord) The texture coordinates associated to this vertex. For Extent the lower left vertex has coordinates (0, 0) and the upper right (1, 1); for Polygon the coordinates at each vertex match the interpolated coordinates that the smallest enclosing extent for that polygon would have at the same fragment; for Point and Multipoint each quad has (0, 0) as the lower left texture coordinate and (1, 1) as the upper right one; for Polyline the start cap is made of two vertices with texture coordinates (0, 0) and (0, 1) while the end cap is associated to (1, 0) and (1, 1).

tessellation-helpers-uv

Distance Valid only for Polyline; it is the distance, in map units, from the beginning of the polyline to this vertex.

tessellation-helpers-distance

Properties: x Number

The x-coordinate, expressed in the same units as the MapView.

y Number

The y-coordinate, expressed in the same units as the MapView.

xOffset Number

The x-offset in screen space; this is used to extrude points (into quads) and polylines, and is 0 for polygons.

yOffset Number

The y-offset in screen space; this is used to extrude points (into quads) and polylines, and is 0 for polygons.

uTexcoord Number

The u-coordinate for texture mapping. It varies between 0 and 1 horizontally for quads and polygons, and along the entire length of a polyline.

vTexcoord Number

The v-coordinate for texture mapping. It varies between 0 and 1 vertically for quads and polygons, and across the width of a polyline.

distance Number

The distance parameter for this vertex; this only applies when tessellating polylines. It starts from 0 and runs up to the total length of the polyline. It is expressed in map units.

Rect Type Definition Rect Object

A rectangle in screen-space.

An instance of Rect is used to specify the screen-space geometry of the resulting marker when calling BaseLayerViewGL2D or BaseLayerViewGL2D. The exact interpretation of "screen-space" is ultimately implemented through a custom vertex shader; a common convention is to interpret the values in the rect as being expressed in pixels or points. See BaseLayerViewGL2D for more details.

tessellation-helpers-uv

Properties: x Number

The x-coordinate of the upper-left corner of the rectangle, relative to the anchor of the marker.

y Number

The y-coordinate of the upper-left corner of the rectangle, relative to the anchor of the marker.

width Number

Width of the rectangle.

height Number

Height of the rectangle.

RenderTarget Type Definition RenderTarget Object

The destination to which render() should direct its output.

Rendering output is saved into a framebuffer, possibly but not necessarily the default one, at a location defined by the viewport.

An instance of this class is mantained internally by BaseLayerViewGL2D and can be accessed by a call to getRenderTarget(). It is the same instance that is restored to the WebGL context by calling bindRenderTarget().

When control is handed over to render(), the WebGL context is guaranteed to be in a default state except for the currently bound framebuffer and the configured viewport. Implementations of render() are free to change these parameters using gl.bindFramebuffer() and gl.viewport(), but they must send the output of the rendering process to the render target.

Properties: framebuffer WebGLFramebuffer

The framebuffer where the render() method should direct its output.

viewport Number []

A viewport that fully covers framebuffer.

ScreenPoint Type Definition ScreenPoint

An object representing a point on the screen.

Properties: x Number

The x coordinate.

y Number

The y coordinate.

TessellatedMesh Type Definition TessellatedMesh Object

The triangle mesh resulting from a tessellation operation.

An instance of Mesh can be obtained by calling one of the BaseLayerViewGL2D tessellate* methods and passing an instance of Geometry.

Properties: vertices MeshVertex []

The vertices that make up the mesh. Each element is a BaseLayerViewGL2D.

indices Number []

The indices of the triangles that connect vertices together; each consecutive triplet of indices denotes a triangle.

Tile Type Definition Tile Object

Represents a tile reference.

Properties: id String

The tile string identifier in the format level/row/col/world

level Number

The level identifier of the LOD to which the tile belongs

row Number

The row identifier.

col Number

The column identifier.

world Number

When the projection allows world wrapping (e.g. Web Mercator), identifies the instance of the world this tile's level/row/col.

resolution Number

The number of map units per pixel in the tile.

scale Number

The map scale at the tile's level.

coords Number []

The coordinates of the top-left corner of the tile as an array of two numbers. The coordinates are in un-normalized map units.

bounds Number []

The bounds of the tile as an array of four numbers that be readily converted to an Extent object.