# GroundPrimitive

#### new Cesium.GroundPrimitive(options)
Scene/GroundPrimitive.js 157

A ground primitive represents geometry draped over terrain or 3D Tiles in the `Scene`.

A primitive combines geometry instances with an `Appearance` that describes the full shading, including `Material` and `RenderState`. Roughly, the geometry instance defines the structure and placement, and the appearance defines the visual characteristics. Decoupling geometry and appearance allows us to mix and match most of them and add a new geometry or appearance independently of each other.

Support for the WEBGL_depth_texture extension is required to use GeometryInstances with different PerInstanceColors or materials besides PerInstanceColorAppearance.

Textured GroundPrimitives were designed for notional patterns and are not meant for precisely mapping textures to terrain - for that use case, use `SingleTileImageryProvider`.

For correct rendering, this feature requires the EXT_frag_depth WebGL extension. For hardware that do not support this extension, there will be rendering artifacts for some viewing angles.

Valid geometries are `CircleGeometry`, `CorridorGeometry`, `EllipseGeometry`, `PolygonGeometry`, and `RectangleGeometry`.

Name | Type | Description
--- | --- | ---

`options`

Object

optional Object with the following properties:

Name | Type | Default | Description
--- | --- | --- | ---
`geometryInstances` | Array | GeometryInstance |  | optional The geometry instances to render.
`appearance` | Appearance |  | optional The appearance used to render the primitive. Defaults to a flat PerInstanceColorAppearance when GeometryInstances have a color attribute.
`show` | Boolean | `true` | optional Determines if this primitive will be shown.
`vertexCacheOptimize` | Boolean | `false` | optional When `true`, geometry vertices are optimized for the pre and post-vertex-shader caches.
`interleave` | Boolean | `false` | optional When `true`, geometry vertex attributes are interleaved, which can slightly improve rendering performance but increases load time.
`compressVertices` | Boolean | `true` | optional When `true`, the geometry vertices are compressed, which will save memory.
`releaseGeometryInstances` | Boolean | `true` | optional When `true`, the primitive does not keep a reference to the input `geometryInstances` to save memory.
`allowPicking` | Boolean | `true` | optional When `true`, each geometry instance will only be pickable with `Scene#pick`. When `false`, GPU memory is saved.
`asynchronous` | Boolean | `true` | optional Determines if the primitive will be created asynchronously or block until ready. If false initializeTerrainHeights() must be called first.
`classificationType` | ClassificationType | `ClassificationType.BOTH` | optional Determines whether terrain, 3D Tiles or both will be classified.
`debugShowBoundingVolume` | Boolean | `false` | optional For debugging only. Determines if this primitive's commands' bounding spheres are shown.
`debugShowShadowVolume` | Boolean | `false` | optional For debugging only. Determines if the shadow volume for each geometry in the primitive is drawn. Must be `true` on creation for the volumes to be created before the geometry is released or options.releaseGeometryInstance must be `false`.

##### Example:

    // Example 1: Create primitive with a single instance
    var rectangleInstance = new Cesium.GeometryInstance({
      geometry : new Cesium.RectangleGeometry({
        rectangle : Cesium.Rectangle.fromDegrees(-140.0, 30.0, -100.0, 40.0)
      }),
      id : 'rectangle',
      attributes : {
        color : new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5)
      }
    });
    scene.primitives.add(new Cesium.GroundPrimitive({
      geometryInstances : rectangleInstance
    }));

    // Example 2: Batch instances
    var color = new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5); // Both instances must have the same color.
    var rectangleInstance = new Cesium.GeometryInstance({
      geometry : new Cesium.RectangleGeometry({
        rectangle : Cesium.Rectangle.fromDegrees(-140.0, 30.0, -100.0, 40.0)
      }),
      id : 'rectangle',
      attributes : {
        color : color
      }
    });
    var ellipseInstance = new Cesium.GeometryInstance({
        geometry : new Cesium.EllipseGeometry({
            center : Cesium.Cartesian3.fromDegrees(-105.0, 40.0),
            semiMinorAxis : 300000.0,
            semiMajorAxis : 400000.0
        }),
        id : 'ellipse',
        attributes : {
            color : color
        }
    });
    scene.primitives.add(new Cesium.GroundPrimitive({
      geometryInstances : [rectangleInstance, ellipseInstance]
    }));

##### See:

- Primitive
- ClassificationPrimitive
- GeometryInstance
- Appearance

### Members

#### readonlyallowPicking : Boolean
Scene/GroundPrimitive.js 340

When `true`, each geometry instance will only be pickable with `Scene#pick`. When `false`, GPU memory is saved.

Default Value: `true`

#### appearance : Appearance
Scene/GroundPrimitive.js 185

The `Appearance` used to shade this primitive. Each geometry instance is shaded with the same appearance. Some appearances, like `PerInstanceColorAppearance` allow giving each instance unique properties.

Default Value: `undefined`

#### readonlyasynchronous : Boolean
Scene/GroundPrimitive.js 356

Determines if the geometry instances will be created and batched on a web worker.

Default Value: `true`

#### classificationType : ClassificationType
Scene/GroundPrimitive.js 217

Determines whether terrain, 3D Tiles or both will be classified.

Default Value: `ClassificationType.BOTH`

#### readonlycompressVertices : Boolean
Scene/GroundPrimitive.js 372

When `true`, geometry vertices are compressed, which will save memory.

Default Value: `true`

#### debugShowBoundingVolume : Boolean
Scene/GroundPrimitive.js 228

This property is for debugging only; it is not for production use nor is it optimized.

Draws the bounding sphere for each draw command in the primitive.

Default Value: `false`

#### debugShowShadowVolume : Boolean
Scene/GroundPrimitive.js 240

This property is for debugging only; it is not for production use nor is it optimized.

Draws the shadow volume for each geometry in the primitive.

Default Value: `false`

#### readonlygeometryInstances : Array|GeometryInstance
Scene/GroundPrimitive.js 200

The geometry instances rendered with this primitive. This may be `undefined` if `options.releaseGeometryInstances` is `true` when the primitive is constructed.

Changing this property after the primitive is rendered has no effect.

Default Value: `undefined`

#### readonlyinterleave : Boolean
Scene/GroundPrimitive.js 308

Determines if geometry vertex attributes are interleaved, which can slightly improve rendering performance.

Default Value: `false`

#### readonlyready : Boolean
Scene/GroundPrimitive.js 388

Determines if the primitive is complete and ready to render. If this property is true, the primitive will be rendered the next time that `GroundPrimitive#update` is called.

#### readonlyreadyPromise : Promise.<GroundPrimitive>
Scene/GroundPrimitive.js 400

Gets a promise that resolves when the primitive is ready to render.

#### readonlyreleaseGeometryInstances : Boolean
Scene/GroundPrimitive.js 324

When `true`, the primitive does not keep a reference to the input `geometryInstances` to save memory.

Default Value: `true`

#### show : Boolean
Scene/GroundPrimitive.js 209

Determines if the primitive will be shown. This affects all geometry instances in the primitive.

Default Value: `true`

#### readonlyvertexCacheOptimize : Boolean
Scene/GroundPrimitive.js 292

When `true`, geometry vertices are optimized for the pre and post-vertex-shader caches.

Default Value: `true`

### Methods

#### staticCesium.GroundPrimitive.initializeTerrainHeights() → Promise
Scene/GroundPrimitive.js 628

Initializes the minimum and maximum terrain heights. This only needs to be called if you are creating the GroundPrimitive synchronously.

##### Returns:

A promise that will resolve once the terrain heights have been loaded.

#### staticCesium.GroundPrimitive.isSupported(scene) → Boolean
Scene/GroundPrimitive.js 414

Determines if GroundPrimitive rendering is supported.

Name | Type | Description
--- | --- | ---
`scene` | Scene | The scene.

##### Returns:

`true` if GroundPrimitives are supported; otherwise, returns `false`

#### staticCesium.GroundPrimitive.supportsMaterials(scene) → Boolean
Scene/GroundPrimitive.js 890

Checks if the given Scene supports materials on GroundPrimitives. Materials on GroundPrimitives require support for the WEBGL_depth_texture extension.

Name | Type | Description
--- | --- | ---
`scene` | Scene | The current scene.

##### Returns:

Whether or not the current scene supports materials on GroundPrimitives.

#### destroy()
Scene/GroundPrimitive.js 867

Destroys the WebGL resources held by this object. Destroying an object allows for deterministic release of WebGL resources, instead of relying on the garbage collector to destroy this object.

Once an object is destroyed, it should not be used; calling any function other than `isDestroyed` will result in a `DeveloperError` exception. Therefore, assign the return value (`undefined`) to the object as done in the example.

##### Throws:

- DeveloperError : This object was destroyed, i.e., destroy() was called.

##### Example:

    e = e && e.destroy();

##### See:

- GroundPrimitive#isDestroyed

#### getGeometryInstanceAttributes(id) → Object
Scene/GroundPrimitive.js 827

Returns the modifiable per-instance attributes for a `GeometryInstance`.

Name | Type | Description
--- | --- | ---
`id` | * | The id of the `GeometryInstance`.

##### Returns:

The typed array in the attribute's format or undefined if the is no instance with id.

##### Throws:

- DeveloperError : must call update before calling getGeometryInstanceAttributes.

##### Example:

    var attributes = primitive.getGeometryInstanceAttributes('an id');
    attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);
    attributes.show = Cesium.ShowGeometryInstanceAttribute.toValue(true);

#### isDestroyed() → Boolean
Scene/GroundPrimitive.js 847

Returns true if this object was destroyed; otherwise, false.

If this object was destroyed, it should not be used; calling any function other than `isDestroyed` will result in a `DeveloperError` exception.

##### Returns:

`true` if this object was destroyed; otherwise, `false`.

##### See:

- GroundPrimitive#destroy

#### update()
Scene/GroundPrimitive.js 644

Called when `Viewer` or `CesiumWidget` render the scene to get the draw commands needed to render this primitive.

Do not call this function directly. This is documented just to list the exceptions that may be propagated when the scene is rendered:

##### Throws:

- DeveloperError : For synchronous GroundPrimitive, you must call GroundPrimitive.initializeTerrainHeights() and wait for the returned promise to resolve.
- DeveloperError : All instance geometries must have the same primitiveType.
- DeveloperError : Appearance and material have a uniform with the same name.