Imagery Requests

The following sections describe the OGC services that are used to obtain Maxar imagery.

Web Map Tile Service (WMTS)

The Web Map Tile Service (WMTS) is use to quickly return imagery tiles for a specified geographical extent. The WMTS specification relies upon the concept of the fact that the surface area of the entire planet can be broken down into predefined set of tiles, which together are referred to as a "tile matrix set". Each tile within the set is uniquely identifiable by a numeric row and column value.

There are several standard tile matrix set specifications, and they are closely related to an underlying Spatial References System (SRS). For example, tile matrix sets exist for both EPSG:3857 (Spherical Web Mercator) and EPSG:4326 (Geographic). Therefore, is necessary to specify the reference tile matrix set for each WMTS request as the platform supports several of them.

Knowing the tileMatrixSet, tileRow, and tileColumn still isn't enough information in order for the service to return an appropriate Tile. This is because the service needs to know at what zoom level the specified Row and Column identifiers apply. A zoom level integer value translates to a corresponding Ground Sample Distance (GSD) on the planet so that the resolution of the imagery can be adjusted according to the apparent distance the tile is from the surface of the planet. Zoom levels start at the furthest distance from the planet surface (zoom level 3) and increase to zoom level 21 as the apparent distance to the planet surface decreases. Therefore, tiles at different zoom levels cover more surface area, and there are fewer and fewer tiles at higher zoom levels. The term "higher zoom level" refers to zoom levels that represent an increase in the apparent distance from the planet.

In summary, a valid WMTS request will include a valid Connect ID, a format, a desired tile matrix set, a zoom level in the tileMatrixSet, the tileRow identifier, and the tileColumn identifier. The following URL is an example of a WMTS request for a specific EPSG:3857 tile at zoom level 17 over San Francisco:

The "Format" parameter of the request specifies the desired return image format. In the previous example, JPEG is the specified tile image format. Though the Maxar use of the JPEG format will result in the quickest service response, several additional formats are supported by the service.

The Maxar OGC tile services will return tiles of quilted imagery using a default imagery stacking profile unless the WMTS includes an optional request parameter that instructs the service to stack the imagery using different criteria such as currency, cloud cover, accuracy, etc. The WMTS request parameter that allows an alternate stacking profile to be specified is named "featureProfile."

Web Map Service (WMS)

The Maxar Web Map Service (WMS) is another OGC service that can be used to obtain imagery. It can also be used to obtain imagery metadata, but we recommend using the Web Feature Service (WFS) in order to obtain imagery metadata. See Metadata Requests for more information about WFS.

WMS provides more flexibility with regard to obtaining imagery in that it is possible to specify a custom geospatial extent, or area of interest, and resolution that is not bound by a tile definition in a specific EPSG tile matrix set. It also allows the request to include additional feature filtering criteria so that it's possible to obtain images that are composed of specific features or features that conform to custom criteria. For example, the Maxar web portal G-EGD uses WMS in order to obtain imagery to fill the user's viewport with 256 x 256 pixel imagery tiles for specific features when the carousel is locked and specific features have been selected in the carousel.

The geographic extent of the desired imagery is specified using the "BBOX" request parameter. "BBOX" is an abbreviation of the term "bounding box". It's value should be a comma separated list of the geospatial coordinates for the lower left and upper right coordinates of a desired rectangular area in the context of the specified Spatial Reference System (SRS). The SRS must be specified in the request as the value of the "SRS" parameter.

An imagery request also requires that the width and height in pixels of the desired resulting image also be specified as the values of the "WIDTH" and "HEIGHT" request parameters. The specified width and height must be proportional to the specified bounding box.

Therefore, valid WMS request will include a valid Connect ID, a format, a bounding box definition, a SRS, and the width and height of the desired image in pixels. The following URL is an example of a WMS request for a EPSG:3857, 256 x 256 pixel image that includes the feature with ID 6505b688b057cb8a6fd9d93baf6618a4 over Louisiana:

In the previous example, WMS was instructed to use only the pixels of the imagery identified by the Feature ID 6505b688b057cb8a6fd9d93baf6618a4. The FEATURECOLLECTION request parameter is one way in which to request that the returned imagery pixels are associated with specific imagery. Another approach is to specify the Common Query Language (CQL) request parameter "Coverage_CQL_Filter" with a value that includes an appropriate filter command.

In summary, WMTS is favored over WMS in terms of speed, but it will be necessary to use WMS when it is necessary for the client application to obtain specialized imagery. Please remember that there are limits to the number of pixels that can be requested in a single WMS call, and that the larger the geographic extent and number of pixels requested, the slower that service will be to respond with the appropriate imagery.

ESRI Tiles

Maxar offers access to tiles via the ESRI Tiles protocol. The following is the base URL: