MvtDataSet Class
A dataset for reading tiled vector data from a Mapbox Vector Tile service, or a local MBTiles file.
NuGet/Assembly: Carmenta.Engine.5.16.2.nupkg (in the CEDataSets assembly)
Syntax
public class MvtDataSet : HttpDataSetRemarks
Introduction
The Mapbox Vector Tile Specification describes a way to encode vector features and attributes into a binary format, a tile. Many vendors use this format to provide entire datasets through an HTTP interface, using tile trees with multiple levels of detail, each level consisting of numerous vector tiles.
Even though there is no standard for these HTTP services, many vendors use similar methods. The MvtDataSet has been tested successfully with several of these, including Carmenta Server version 4.6. Many vendors also provide different types of metadata, usually in the form of a JSON document. MvtDataSet tries to read this metadata and makes use of the information that is recognized.
An MvtDataSet can also be used to read vector tiles from a local MBTiles file instead of a remote HTTP service. But note that MBTiles files can also store raster tiles; use MapPackageDataSet to read those. MVT data that is contained in geopackages (.gpkg) files must also be read using MapPackageDataSet.
Metadata
The metadata document, if available, may hold information about available sub-layers in the tiles, and possibly a list of attribute names and types. This information is made available through the GetDataSetInfo method. If you load a configuration with an MvtDataSet in Carmenta Explorer, you can use the DataSets and Properties panels to look at the available information.
Configuration
To use an MvtDataSet, you typically set the Url property to the full URL of the metadata document for the tileset you wish to use. You can also set the property to a template URL for loading tiles, something like "http://server/path/{z}/{x}/{y}.pbf". No metadata will be available, but the dataset should be able to load tiles from the service.
To read tile from a local MBTiles file instead, specify the Path and FileName properties, and leave Url blank.
You should put your layer with MVT data under a TileLayer for efficient caching. However, due to the way TileLayer renders its sub-layers, you may need to render your MVT polygon, line and point features in separate layers. Otherwise a polygon from one tile may partly obscure for instance a text extruding from a neighboring tile.
You should also set TileLayer.TilingScheme to GoogleMapsCompatible to avoid some rendering artifacts that may otherwise occur if the tiles from the dataset do not match the tiles of the layers.
Carmenta Server 4.6 can provide additional services, indicating how to render MVT features on the client. The MvtDataSet will retrieve this information when available, and automatically create the necessary visualizers and attach to the features it generates. When used with another service provider, the visualization will have to be configured the usual way in Carmenta Studio.
Each MvtDataSet reads just one tileset, even though the tiles in it may contain several sub-layers. Some service providers, including Carmenta Server, offer ways to request just some of these sub-layers, as separate tilesets. But there is currently no way to automatically discover which tilesets are available, you must check with your service provider.
Features created by the MvtDataSet will all be given a layer attribute indicating the name of the sub-layer the feature belongs to.
Inheritance Hierarchy
System.Object (not available in C#)
EngineObject
ResourceObject
DataSet
HttpDataSet
MvtDataSet
Platforms
Windows, Linux, Android
MvtDataSet Members
The MvtDataSet type has the following members.
Constructors
| Name | Description |
|---|---|
| MvtDataSet | Initializes a new instance of the MvtDataSet class. |
Properties
| Name | Description |
|---|---|
| Description | Gets or sets a short description of the dataset. Inherited from DataSet |
| DisplayName | Gets or sets a display name for the dataset. Inherited from DataSet |
| FileName | Gets or sets the name of a local MBTiles file to read from. |
| Id | Gets a unique identifier for this dataset instance. Inherited from DataSet |
| IsDisposed | Gets a value that tells whether the current MvtDataSet has been disposed. Inherited from EngineObject |
| IsoMetadataDocument | Gets or sets the path to an ISO 19139 metadata document for the dataset. Inherited from DataSet |
| Name | Gets or sets the name of the MvtDataSet. Inherited from ResourceObject |
| NativeHandle | Gets the native Carmenta Engine kernel object the current MvtDataSet represents. Inherited from EngineObject |
| Password | Gets or sets the password used for basic authentication on the server. Inherited from HttpDataSet |
| Path | Gets or sets the directory of a local MBTiles file to read from. |
| ServiceMonitorInterval | Starts a background thread that monitors the web service for changes. Inherited from HttpDataSet |
| SuppressInitializationErrors | Gets or sets a flag indicating how errors during dataset initialization are handled. Inherited from DataSet |
| ThrowExceptions | Gets or sets a flag indicating if exceptions should be thrown when an error occurs. Inherited from HttpDataSet |
| Timeout | Gets or sets a value indicating how long the dataset will wait for a response from the web service. Inherited from HttpDataSet |
| Url | Gets or sets the URL of the web service instance that the dataset should connect to. Inherited from HttpDataSet |
| User | Gets or sets the username used for basic authentication on the server. Inherited from HttpDataSet |
| IUserProperties.UserProperties | Gets the AttributeSet that contains the user properties. Inherited from IUserProperties |
Methods
| Name | Description |
|---|---|
| Clone | Creates a copy of an object. Inherited from EngineObject |
| Dispose | Releases the reference to the native Carmenta Engine kernel instance the EngineObject represents. Inherited from EngineObject |
| Equals | Determines whether this instance is equal to another. Inherited from EngineObject |
| FindChildObject | Overloaded. Finds the child object with the specified name. Inherited from DataSet |
| FlushCache | Frees any information the dataset may have cached, including all cached features. Inherited from DataSet |
| GetChildObjects | Overloaded. Gets the child objects of the current object. Inherited from DataSet |
| GetDataCoverage | Gets coverage information for this dataset in a given area. Inherited from DataSet |
 GetDataSetById | Looks up an existing dataset instance from a dataset identity. Inherited from DataSet |
| GetDataSetInfo | Returns a dataset info that describes the contents of this dataset. Inherited from DataSet |
| GetDataSetInfoAsync | Makes an asynchronous call to GetDataSetInfo. Inherited from DataSet |
| GetFeature | Gets the feature with the specified identity. Inherited from DataSet |
| GetFeatures | Overloaded. Gets features from the dataset. Inherited from DataSet |
| GetFloatValueAt | Overloaded. Gets the float raster value from a cell at the specified position. Inherited from DataSet |
| GetFloatValuesAt | Overloaded. Gets a number of float raster values. Inherited from DataSet |
| GetLocalizedDescription | Gets a localized version of the dataset description in a specific language. Inherited from DataSet |
| GetLocalizedDisplayName | Gets a localized version of the dataset display name in a specific language. Inherited from DataSet |
| GetLocalizedIsoMetadataDocument | Gets the path to an ISO 19139 metadata document for a specific language. Inherited from DataSet |
| GetNormalizedFloatValueAt | Overloaded. Gets the raster value from a cell at the specified position, normalized by Scale and Offset. Inherited from DataSet |
| GetNormalizedFloatValuesAt | Overloaded. Gets a number of raster values, normalized by Scale and Offset. Inherited from DataSet |
| GetValueAt | Overloaded. Gets the integer value from a raster cell at the specified position. Inherited from DataSet |
| GetValuesAt | Overloaded. Gets a number of raster values. Inherited from DataSet |
| HasLocalizedDescription | Checks if a localized version of the dataset description is available in a specific language. Inherited from DataSet |
| HasLocalizedDisplayName | Checks if a localized version of the dataset display name is available in a specific language. Inherited from DataSet |
| HasLocalizedIsoMetadataDocument | Checks if an ISO 19139 metadata document is available for a specific language. Inherited from DataSet |
| HighestRasterValue | Finds the highest raster value inside the given polygon. Inherited from DataSet |
| Initialize | Initializes the dataset. Inherited from DataSet |
| Reset | Resets the HttpDataSet instance to its default state. Inherited from HttpDataSet |
| SetLocalizedDescription | Sets a dataset description in a specific language. Inherited from DataSet |
| SetLocalizedDisplayName | Sets a dataset display name in a specific language. Inherited from DataSet |
| SetLocalizedIsoMetadataDocument | Sets the path to an ISO 19139 metadata document for the dataset, for a specific language. Inherited from DataSet |
| TryGetFloatValueAt | Overloaded. Gets the float value from a raster cell at the specified position. Inherited from DataSet |
| TryGetNormalizedFloatValueAt | Overloaded. Gets the float value from a raster cell at the specified position, normalized by Scale and Offset. Inherited from DataSet |
| TryGetValueAt | Overloaded. Gets the integer value from a raster cell at the specified position. Inherited from DataSet |
Events
| Name | Description |
|---|---|
| ServiceChanged | Occurs when the HttpDataSet has detected changes to the web service. Inherited from HttpDataSet |