Metadata Requests

Maxar provides access to feature metadata via the Web Feature Service (WFS). WFS is used to obtain the metadata that corresponds to imagery that was returned from a WMTS or WMS request, or to discover all available images at a particular location perhaps prior to submitting an imagery request.

The WFS returns imagery metadata in the GML format by default.

Maxar offers the following feature types:

• DigitalGlobe:FinishedFeature
  • All of the strips and mosaics
  • Orthorectified 1:12,000 to 1:50,000
  • Acquisition Date and Feature ID are critical attributes
• DigitalGlobe:ImageInMosaic
  • Shows Seamlines of a mosaic of a FinishedFeature
  • Acquisition Date and parentFeatureID is provided
• DigitalGlobe:TileMatrixFeature
  • Metadata for a tile identified by the tile matrix set, row, and column

FinishedFeature

The following is a basic WFS call using a HTTPS POST for DigitalGlobe:FinishedFeature feature type. This can be done in parallel with a raster call for a defined geographical extent. The following URL is an example of a WFS FinishedFeature request:

The following GML is included as the body of the HTTP request:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
<?xml version="1.0" encoding="utf-8"?>
<GetFeature xmlns="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:gml="http://www.opengis.net/gml" service="WFS"
            version="1.1.0" outputFormat="text/xml; subtype=gml/3.1.1" maxFeatures="100" handle="">
    <Query typeName="DigitalGlobe:FinishedFeature" srsName="urn:x-ogc:def:crs:EPSG:4326">
        <ogc:Filter>
            <ogc:Intersects>
                <ogc:PropertyName>geometry</ogc:PropertyName>
                <gml:Envelope srsName="urn:x-ogc:def:crs:EPSG:4326" xmlns:gml="http://www.opengis.net/gml">
                    <gml:lowerCorner>37.80811 -122.41276</gml:lowerCorner>
                    <gml:upperCorner>37.81163 -122.40817</gml:upperCorner>
                </gml:Envelope>
            </ogc:Intersects>
        </ogc:Filter>
    </Query>
</GetFeature>

This GML is used to specify the geospatial coordinates of a bounding box in the context of the EPSG:4326 Coordinate Reference System (CRS). The order of the coordinates in EPSG:4326 is longitude/latitude. If you specify WFS1.1 as a version the order of coordinates is latitude/longitude.

It is not necessary to specify the parameters of the request as GML in the body of the request. WFS accepts many request parameters that can be specified in the URL to achieve the same result as what would otherwise be specified in the body of a request. When the request parameters are included in the URL rather than as a GML payload in the request body, then an HTTP GET request may be used for the request instead of a POST request.

Maxar has added a width and height parameters to the WFS protocol to enable scale to be defined. It is recommended that developers include width and height with every request to ensure what is the resulting data is correct based on the scale defined by the width and height.

The "showTheRasterReturned" request parameter must be included in the request if the desire is to obtain imagery metadata that corresponds to a given raster output from WMS. The absence of this parameter results in all imagery metadata for that area being returned, which is what you would want if you plan to support multi-temporal.

TileMatrixFeature

A TileMatrixFeature is an easy way to obtain the metadata associated with an equivalent imagery tile request from WMTS. By being able to refer to a specific WMTS tile, it is not necessary to convert the geometry of a tile to that of a BBOX, width, and height as would otherwise be required by the standard WFS request syntax. It is recommended that this be done only on demand within the user interface, otherwise you have too many corresponding requests for a typical tiled viewport.

The following URL is an example of a WFS TileMatrixFeature request for the EPSG:3857 tile in row 58685 and column 39235 at zoom level 17:

Stacking Profiles, Filters, and Result Sorting

Stacking Profiles

Applications that construct maps of terrain using Maxar services must deal with the fact that a large number of high resolution images (features) of that terrain are available in the Maxar catalog and that each of those features has a number of different attributes. In some cases a single feature will cover the entire AOI. In other cases many features may be needed to create an entire map, each providing one piece of the overall image. If a large number of features are available, any given part of the AOI could be filled by any of a number of different features. Those features each have different attributes which may be preferable or undesirable depending on the intended goal for the final map.

Stacking profiles are defined based upon those attributes that are most important to most Maxar imagery applications. Maxar customers select a stacking profile that reflects those preferences and that stacking profile is used to assemble the features into a mosaic that best satisfies those preferences. They are referred to as "stacking profiles", because they determine how a number of features are stacked to cover a given geographic extent.

A target stacking profile name may be specified in the WFS using the "featureProfile" request parameter. It is not necessary to specify a stacking profile as a parameter to a WFS request. When no stacking profile parameter is specified with a request, then the default stacking profile that is associated with the account that is represented by the Connect ID parameter will be used as the basis for all other filter criteria that are specified with the request.

If selecting features using a custom CQL-based filter via the "CQL_Filter" request parameter is preferable outside of a stacking profile, then specify the "Default_Profile" as the stacking profile for the request. The default profile returns available features at all zoom levels. In addition, when multiple features are available, they are generally stacked in chronological order.

	For detailed information related to Maxar imagery stacking profiles, please refer to Stacking Profiles.

Filters

The "CQL_Filter" parameter is used specify custom imagery filtering criteria. This parameter takes a value that conforms to the Common Query Language (CQL) format. CQL is a formal language for representing queries to information retrieval systems. Imagery filtering criteria can be specified for one or more imagery attributes using logical comparison operators. For example, the following WFS request includes a CQL filter that filters all imagery with an ingest data that is less than or equal to "2017-04-09" and has greater than or equal to 15% cloud cover.

	https://evwhs.digitalglobe.com/catalogservice/wfsaccess?request=GetFeature&typeName=DigitalGlobe:TileMatrixFeature&SERVICE=WFS&VERSION=1.1.0&connectId=<CONNECTID>&CQL_FILTER=layer=((ingestDate>'2017-04-09')AND(cloudCover<.15))

	For detailed information about the CQL and how to use it in the context of service requests, please refer to Common Query Language.

Result Sorting

The "SORTBY" request parameter is used to specify a list of feature attributes upon which the features that are included in the result set are sorted. Optional text after the property name indicates whether the attribute value should be sorted in ascending or descending order. The default order is ascending. For example, in the following request, the result set will be sorted first in descending order by the value of the acquisitionDate attribution and then in ascending order by offNadirAngle.



https://services.digitalglobe.com/catalogservice/wfsaccess?request=GetFeature&typeName=DigitalGlobe:TileMatrixFeature&SERVICE=WFS&VERSION=1.1.0&connectId=<CONNECTID>&CQL_FILTER=layer='DigitalGlobe:ImageryTileService'and%20tileMatrixSet%20=%20'EPSG:3857'%20and%20tileMatrix%20=%20'EPSG:3857:17'%20and%20row%20=%2058685%20and%20column%20=%2039235&SORTBY=acquisitionDate%20D,offNadirAngle%20A

WFS API Resources

This document is not intended to be a comprehensive guide for the use of the Maxar WFS service. Please refer to WFS for a complete description of request parameters, CQL filters, and additional examples of WFS requests.