Connected Systems SWG

The 127^th OGC Member Meeting

Alex Robin, Sensiasoft / GeoRobotix

25 September 2023

​

1

Meeting

sponsors

SWG Progress Report

• Reviewer’s Guide
• SensorML JSON Schemas
• Alignment with Feature API logical schema approach
• Currently finalizing different aspects of the specification:
• Experiments with Sampling Features
• Experiments with different kinds of Hierarchical Systems
• Experiments with linking to WMS/WCS or Coverage/Maps API
• Experiments with generic binary formats (Protobuf, Flatbuff, Avro, etc…)
• OSH Implementation

2

SWG Roadmap

• Finalize Reviewer’s Guide - 10/2023
• Finalize SensorML Extensions - 10/2023
• Finalize CS API Part 1 - 11/2023
• Finalize CS API Part 2 - 11/2023
• OGC API Connected Systems ready for review - 11/2023

3

SWG Resources

4

• GitHub Site�https://github.com/opengeospatial/connected-systems
• Many examples in repo�https://github.com/opengeospatial/connected-systems/tree/master/api/part1/openapi/examples�https://github.com/opengeospatial/connected-systems/tree/master/api/part2/openapi/examples�https://github.com/opengeospatial/connected-systems/tree/master/api/usecases
• OpenAPI specs:�https://github.com/opengeospatial/connected-systems/blob/master/api/part1/openapi/openapi-connectedsystems-1.yaml�https://github.com/opengeospatial/connected-systems/blob/master/api/part2/openapi/openapi-connectedsystems-2.yaml�

​

​

​

SensorML JSON Schema�+ Extensions

5

SensorML Extensions

• Added Deployment and DerivedProperty classes
• Added JSON Schema
• Changes from XML encoding
• name -> label (conflict btw ‘name’ attribute and ‘name’ element from XML)
• Single lists for identifiers, classifiers, keywords, contacts, documents.
• Keep multiple lists for characteristics / capabilities
• Position as GeoJSON Point, SWE Vector or Pose (GeoPose)
• Position by linking to Datastream (remove process option)
• Use weblinking JSON for references (typeOf, components, etc…)

​

6

Logical Schemas

7

Formats Used

8

Feature API Logical Schema

• Goal is to align with logical schema approach of Feature API (future Part 5?)
• Logical schema = Encoding independent description of feature properties for a given collection
• CSAPI also uses the approach to describe observation results/parameters (via DataStream resource) and command parameters (via ControlStream resource)
• Encoding specific schemas also provided (links back to property description in the logical schema)
• SWG decided to use SWE Common JSON as our logical schema language as the modified JSON Schema language used by Feature API Part 5 doesn’t provide all needed functionality yet (future revisions will align on Part 5 if appropriate)
• Make it work with Protobuf and FlatBuffers

​

9

Example: Logical Schema with Protobuf

10

syntax = "proto3";

import "google/protobuf/timestamp.proto";

​

message Observation {

/* datastream ID */

optional int64 datastream_id = 1;

​

/* sampling feature ID */

optional int64 sf_id = 2 [ default = 0 ];

​

/* sampling time */

Timestamp time = 3 [ (schema_ref) = "phenomenonTime" ];

​

/* pan (deg) */

float pan = 1 [ (schema_ref) = "result/pan"];

/* tilt (deg) */

float tilt = 2 [ (schema_ref) = "result/tilt" ];

​

/* zoom factor (%) */

float zoom = 3 [ (schema_ref) = "result/zoom" ];

}

​

"resultSchema": {

"type": "DataRecord",

"fields": [

{

"name": "pan",

"type": "Quantity",

"definition": "http://sensorml.com/ont/swe/property/PanAngle",

"label": "Pan Angle",

"description": "Rotation of the camera around its vertical axis...",

"uom": {

"code": "deg"

}

},

{

"name": "tilt",

"type": "Quantity",

"definition": "http://sensorml.com/ont/swe/property/PanAngle",

"label": "Tilt Angle",

"description": "Rotation of the camera around its horizontal axis...",

"uom": {

"code": "deg"

}

},

{

"name": "zoom",

"type": "Quantity",

"definition": "http://sensorml.com/ont/swe/property/ZoomFactor",

"label": "Zoom Factor",

"description": "Amount of zoom, 0 being the highest FOV and 100 being the lowest",

"uom": {

"code": "%"

}

}

]

}

​

Protobuf Schema (.proto)

Logical Schema (SWE Common JSON)

"result": {

"pan": 145.0,

"tilt": 16.5,

"zoom": 25,

}

Hierarchical Systems

11

Hierarchical Systems - 1

• Use Cases: Different kinds of hierarchical Systems in scope
• Systems with built-in components
• Systems with interchangeable components/payloads
• Groups of Systems (Sensor Networks, etc.)
• Teams of persons carrying sensors or acting as sensors

​

• Modeled with different combinations of Procedures / Systems / Deployments

​

12

Hierarchical Systems - 2

• In the API, components (a.k.a sub-systems) can be described:
• At the procedure level
• At the system (instance) level
• At the deployment level
• Procedure Level�Components are described as part of a procedure (i.e. "system model") if they are not designed to be interchangeable in each instance.
• System Level�Components are described as part of the system (instance) if they can be combined differently in each instance, but don't change often during the lifetime of the system.
• Deployment Level�Components are attached to a parent system at deployment time if they are interchangeable payloads (i.e. they can be changed during the lifetime of the parent system)

13

Hierarchical Systems - 3

• Procedure/System components can be described either:
• Inline as part of the parent description
• As a separate resource referenced from the parent description

​

• Same pattern as UML composition vs. aggregation

​

• Inline = UML composition: When components don't exist independently of the parent (i.e. they cannot be purchased separately / cannot be shared by multiple procedures or system instances) - ex: MavicPro�
• By Reference = UML aggregation: Components are described as separate resources and linked if they can be reused as part of multiple procedures or attached to different parent systems at different times - ex: Saildrone, Nexrad

14

Sampling Features

15

Sampling Features

• New Sampling Features defined in OGC API - Connected Systems
• SamplingSphere with center and radius
• SamplingFrustum (used for remote optical sensors, e.g. video cam, spaceborne EO instruments, etc.)
• FeaturePart to identify a part of a feature of interest by name (e.g. CPU, fuel tank, engine, etc.)
• TBD
• SamplingEllipsoid with center, major and minor radiuses
• RadarLobe?

​

16

Mobile Sampling Features - 1

• Extension of Spatial Sampling Features to provide position/pose relative to other system (platform)

• Saildrone Example

Several sampling features moving along with the platform

• need at least 3 sampling features since they have different sampled features
• don’t want to insert separate locations for each sampling features
• better to express position relative to platform

17

Web Links

18

General Approach for Links

• Two types of links:
• as resource properties (with @link suffix)
• in ‘links’ array�
• Use links within the resource itself when part of the model (i.e. everything that would be provided with the resource on POST/PUT)�
• Use ‘links’ array for auxiliary links (often auto-generated by server) such as:
• self link
• canonical URL
• alternate encoding formats

19

Links to External Resources

• Use JSON profile of Web Linking (RFC8288)�
• Use RFC 6690 to identify target API
• defines additional link properties (beyond ‘href’, ‘title’ and media type)
• ‘if’ = interface type: used to identify target service or API (e.g. API Coverages)
• ‘rt’ = resource type

20

Links to Domain Features - 1

• Can link to external domain features

21

Observation

System

Domain�Feature

Sampling

Feature

Link�href = URL of Feature resource �if = http://www.opengis.net/spec/ogcapi-features-1/1.0

e.g. GW_Aquifer�HY_River, HY_Lake

(Proxy)

Feature

Link�rel = alternate�

Links to Domain Features - 1

22

{

"type": "Feature",

"id": "SP001",

"geometry": {

"type": "Point",

"coordinates": [ 12.31, -86.98]

},

"properties": {

"uid": "urn:x-usgs:sites:301244087575701",

"name": "USGS Site #301244087575701",

"description": "Well at MOBILE RIVER SAWMILL CORP",

"featureType": "http://www.opengis.net/def/samplingFeatureType/OGC-OM/2.0/SF_SamplingPoint",

"sampledFeature@link": {

"href": "https://api.usgs.gov/collections/hydrological_features/items/112TRRC?f=json",

"type" : "application/geo+json",

"title": "Aquifer 112TRRC",

"if": "http://www.opengis.net/spec/ogcapi-features-1/1.0",

}

},

"links": [

{

"href" : "https://data.example.org/api/samplingFeatures/SP001?f=json",

"rel" : "self",

"type" : "application/geo+json",

"title" : "this document"

}, {

"href" : "https://data.example.org/api/samplingFeatures/SP001?f=html",

"rel" : "alternate",

"type" : "text/html",

"title" : "this resource as HTML"

}

]

}

​

​

​

​

Links to Coverage Results - 1

• Can link an Observation Result to external Coverage resource�(e.g. Coverages API, Maps API, WCS, WMS)

23

Datastream

System

External�Coverage

Embedded Result

Link�href = URL of coverage resource �if = http://www.opengis.net/spec/ogcapi-coverages-1/1.0

rt = Coverage�

Observation

Links to Coverage Results - 2

24

{

"id": "fefaig45w46v5186d6w",

"datastream@id": "f44f85rrt",

"foi@id": "55f48g48th",

"phenomenonTime": "2023-04-03T18:45:23Z",

"resultTime": "2023-04-03T18:45:23Z",

"result@link": {

"href": "https://data.x-ecmwf.int/wms?service=WMS&version=1.1.0&request=GetMap&format=image/tiff&� layers=HRES-2T-20230215-0600-T1&bbox=-180,90,180,-90&width=3600&height=1800&srs=EPSG:4326",

"title": "Imagery on external WMS server",

"type": "image/tiff; application=geotiff",

"if": "http://www.opengis.net/def/serviceType/ogc/wms/1.1"

}

}

OpenSensorHub Demo

25

OpenSensorHub Demo

• Hierarchical Systems (Procedures and Systems)
• Sampling Features
• Links to Ontologies

​

26

Thank you!

27