Web Datasource Introduction

The Web engine can access the service provided by WFS, WMS, WCS, REST and services provided by others, this kind of engine process the Web server that meet the industrial standard on the internet as SuperMap datasource, the map and data published by the network can be combined with the SuperMap map or data, and blend in SuperMap technical system and expand to application area of SuperMap data engine. Web datasource is a read only engine.

supports the following Web datasources:

    1. OGC standard service (W*S)

    2. REST service

    3. GoogleMaps service

    4. MapWorld service

    5. OpenStreetMap service

    6. ChinaRS

    7. Global Topographic Map service

    8. Service example

OGC standard service (W*C)

About OGC

  • GML: Geography Markup Language, it uses the OGC sample object model, and orginze the file based on XML syntax and file format.
  • URI: Uniform Resource Identifier. Open OGC service with desktop client, it is needed to input the address of the request body, or the URI. It is composed of three parts: The naming method of the resource to visit, the host name stores the resource. The name of the resource is represented by path. The path structure is http://:/iserver/services. In which: .
    • server: The service address that publish the service.
    • port: The port publish the service.
    • servicecomponent: the name of the service component or service component collection, for example, map service component map-world is configured in SuperMap iServer by default.
    • serviceinterface: The service interface name configured and bound by the service component, for example, SuperMap iServer configured WMS 1.1.1 service interface by default, the name of the service interface is wms111.
  • Version Number Negotiation: The version of the OGC network service standard have high or low version, and is identified by numbers. Generally, the version achieved or supported on client and the server are different, version number negotiation defines the rule to achieve the synchronous of versions on the client and the server.
    1. If the version number requested by the client is achieved on the server, the server must sent the data of this version.
    2. If the version number requested by the client is a high version that can not be identified by the server, the server must send the highest version in the versions lower than the requested version.
    3. If the version number requested by the client is a version lower than all the versions supported by the server, the server should send the lowest version it supports.
    4. If the client can identify the version returned from the server, it will stop the communication with the server, and request a recognizable version lower than the version returned.
    5. If the version requested by the client is lower than all the versions supported by the server, according to rule 3, the server response with the lowest version, but the client still can't identify this high version, then the client sent a request higher than the server response version.
    6. The version number negotiation will go on until the two parts reach a version available or the client can't interact with the server.

OGC service introduction

  • WMS service

    • WMS (Web Map Service) accord with the WMS realizing standard established by OGC (Open Geospatial Consortium). This standard define the three operations used to create and display map: GetCapabilities, GetMap and GetFeatureInfo.

    1. GetCapabilities is used to get service-level metadata. Required.
    2. GetMap, the core operation, this operation is used to get geospatial parameter and map image with the definite size. Required.
    3. GetFeatureInfo, this operation is used to get some spatial features on the map. Optional.

    Current, supports the following WMS versions:

    • WMS 1.1.1
    • WMS 1.3.0
  • WFS service

    WFS: Web Feature Service, this service meets the WFS implementation specification set by the OGC (Open Geospatial Consortium). This standard is mainly used to return the feature-level GML code. WFS allows clients to get the geospatial data with GML code from several network feature service. Different WFS clients support different character sets, so when sending requests, the coding types of the request bodies are also different.

    • Note

    Current the function supported by WFS datasource includes only browsing data

  • WCS

    • WCS (Web Coverage Service) meets the WCS implementation specification defined by Open Geospatial Consortium.

    WCS is a specification defined by OGC to share geospatial data in form of Coverage on the Web. Coverage is a data that can return the value of any point, it is easy to import to models. WCS share raster and image dataset in form of Coverage.

    Currently, supports opening WCS 1.0.0 data.

  • WMTS
    1. The raise of WMTS

      2. WMS map service can response to all kinds of requirements flexibility, for every request sent by the client, the server will visualize the data in real time and return the result in form of image, but when there are large visitor volume, the frequent request will occupy lots of resource for computing, and this may lead to the fall of the response ability. To provide the corresponding ability for map service, it is needed to reduce the visualization time on the server, the services which improve the visualization ability in form of cache is raised, and WMTS is one of them.

    2. The concept of WMTS

      3. WMTS (Web Map Tile Service), this service meets the WMTS specification specified by OGC. WMTS defines some operations, these operations allow users to visit tile map and it is the first service specification that OGC supports REST visit.

      WMTS is a cache specification raised by OGC, it provides a standard scheme to publish map service in form of predefined tile. The map tile of certain size is cached on the server and only provide the service of the defined single tile for the client, more data processing operations like layer overlap is done on the client, this may reduce the data processing pressure on the GIS server and improve the user experience.

      WMTS uses tile matrix set to represent the map tiled, as shown in fig1. Tiles are the matrix unit that contains geographic data. A map is tiled into several tiles with certain tile size, and the result is tile matrix. One or more tile matrix will form a matrix set. Different tile matrixes have different scales, and every tile matrix is identified by an ID (usually the index of the tile matrix, the layer with the lowest resolution is the 0 layer, and so forth). WMTS defines how many tile matrix sets each layer can have, each tile matrix set has its own coordinate system, the tile matrixes in a matrix set is corresponding to the scales.

      Figure 1: Tile matrix set.

      Each tile matrix has the following characteristics:

      • Uses it own tile size as the scale.
      • Define the height (TileHeight) and width (TileWidth) in pixels, that is the size of the tile.
      • The top left coordinate of the matrix bounding box (TileMatrixminX, TileMatrixmaxY).
      • Define the width (MatrixWidth) and height (MatrixHeight) of the matrix in number of tiles.

      The tiles in the tiles matrix is identified with the row number (TileRow) and the column number (TileCol), both starts from the tile at the top left point, the start value is (0,0), and increase downwards and rightwards.

      Figure 2: Tile matrix.
    3. WMTS implement model

      4. WMTS 1.0.0 support three implement models:

      • HTTP KVP (Key-Value Pair) mode
      • SOAP mode
      • REST mode

      Currently, provides two modes: KVP and REST.

      The resource requested form WMTS can be the procedure-oriented architectural style or resource-oriented architectural style. From the concept of procedure-oriented, WMTS 1.0.0 defines three operations: GetCapabilities, GetTile and GetFeatureInfo, in which GetFeatureInfo is an optional operation. Form the concept of resource-oriented, WMTS 1.0.0 defines three resources: ServiceMetadata, Tile and FeatureInfo, corresponding to GetCapabilities, GetTile and GetFeatureInfo respectively.

      1. GetCapabilities, returns service metadata (ServiceMetadata), that is the service ability and the information contents.
      2. GetTile, return tile map.
      3. GetFeatureInfo, returns the feature information displayed on the tile map, optional operation.

For more information about OGC, see http://www.opengeospatial.org.

REST service

REST-Representational State Transfer is a software architectural style raised by Dr Roy Fielding in 2000. The Web service with REST architectural style is more simple and easy to use than the copied SOAP service. The REST service of SuperMap provides the REST style CIS service.

REST emphasizes to view the whole network form the resource, the architecture based on REST is a resource-oriented architecture (ROA). Resources can be concrete data or some service that can implement certain functionalities, the application of the client is identified by URI (Uniform Resource Identifier), the application of the client use URI to get the representation of the resource, the application status of the client application will be changed in getting these representation.

REST usually uses the popular standards like HTTP, URI, XML and HTML. SuperMap UGC REST service have the following characteristics:

  1. Every resource provided by the server have one or more URIs.
  2. REST service use HTTP protocol standard methods, including GET, POST, PUT, DELETE, etc.
  3. Provide several kinds of representations for the resource, like xml, json and html.
  4. All the information needed for REST service to process the resource request is contained in the request.

GoogleMaps service

For Google map service, read only, and cannot create.

Google Maps contains vector map, remote sensing image of different resolutions and some terrain data. inherits GoogleMaps engine, users can visit the Google Maps service in it with the network. Currently, the following map types are supported:

  • roadmap: Standard route map, such as the common map displayed in Google Maps website.
  • satellite: The satellite image layer.
  • terrain: The map is used to display the terrain and vegetation.
  • hybrid: It contains the mixed layers of satellite image and path map. It is a transparent layer that displays the main street and address name.

GoogleMaps website: http://maps.google.com

Note: Users from China can't access the default url: http://maps.google.com, but users from other countries can use the function normally.

      Users from China can access http://www.google.cn/maps and then browse map.

MapWorld service

The map service for MapWorld, read only, and cannot create.

MapWorld service is the authoritative, believable and unified geographic information service provided by the national administration of surveying, mapping and geoinformation of China. integrates the Tianditu engine. When the network is connected, you can access the Tianditu service directly in the product. The supported layer types are:

  • BackgroundMap: The background layer. It can be as the base map.
  • AnnoMap: Chinese annotation layer.
  • AnnoMapE: English annotation layer.
  • Terrain: The map can be loaded to the scene directly. The coordinate system is WGS_1984.

MapWorld website: www.tianditu.cn

OpenStreetMap

OpenStreetMap (OSM for short) is a world map that can be edited. OSM is an online map cooperation plan. It aims at creating a world map with free contents and edit.

OSM map data were authorized in the format of open database. The data can be loaded free, and it is used according to the open license agreement. Usrs can upload the handheld device, aerial photographs and satellite images. They can also edit the map vector data.

Currently, it supports the following layers:Standard, Cycle Map, Transport Map and MapQuest Open.

OpenStreetMap website:www.openstreetmap.org

ChinaRS

For ChinaRS, read-only, can not be created.

ChinaRS service is a variety of remote sensing images map service provided by ChinaRS. You can directly access online data services in desktop products, if the network is connected. Four data services are currently available, they are 2014 Gaofen-1 Image Map Service, 2013 Huadu ZY-3 Image Map Service, 2016 Second Quarter PL Image Map Service and 2016 Third Quarter PL Image Map Service.

ChinaRS website: www.chinarsgeo.com/

Global Topographic Map

Global topographic map services can be divided into two classes: basic topographic map service and dark topographic map service. They are created based on the global hill-shading map in the form of raster tiles. The services use shade and color gradients to express the terrain changes. Overlaying data like vegetation, towns, glaciers, wasteland, etc., the two classes of map services can help users to exhibit specific thematic features as a base map.

Each topographic map service has ten map scales. The resolutions of terrain data on each scale are different from each other to present a much better effect. Data with different resolutions are obtained by resampling DEM with the resolution is 1800m.

The basic topographic map service is lighter-colored terrain data, while the dark topographic map service is blue-black terrain data. You can access data via the following addresses.

Fundamental topographic map: https://maptiles.supermapol.com/iserver/services/map-Hillshade/rest/maps/WorldTerrainBase

Dark topographic map: https://maptiles.supermapol.com/iserver/services/map-Hillshade/rest/maps/WorldTerrainBlueDark

Service example

Users can visit the following addresses to experience the services provided by iServer.