# OPC UA Relative Spatial Location and Global Positioning

The Positioning libraries implement two OPC UA companion specifications:

- Relative Spatial Location (RSL), defined by
  [OPC 10000-210](https://reference.opcfoundation.org/specs/OPC-10000-210).
- Global Positioning (GPOS), defined by
  [OPC 10000-211](https://reference.opcfoundation.org/specs/OPC-10000-211).

The libraries use the released RSL 1.00.1 and GPOS 1.0.0 NodeSets. GPOS
depends on RSL.

## Contents

- [Packages](#packages)
- [Minimal standalone server](#minimal-standalone-server)
- [Server authoring](#server-authoring)
- [Client](#client)
- [Transform conventions](#transform-conventions)
- [Robot and OpenUSD sample](#robot-and-openusd-sample)

## Packages

| Package | Purpose |
|---|---|
| `OPCFoundation.NetStandard.Opc.Ua.Positioning` | Source-generated RSL and GPOS models plus frame, WGS84, ENU, and ground-control-point transformations. |
| `OPCFoundation.NetStandard.Opc.Ua.Positioning.Server` | Standalone/composed node-manager hosting, address-space builders, providers, lifecycle, validation, and logging. |
| `OPCFoundation.NetStandard.Opc.Ua.Positioning.Client` | Continuation-safe discovery, typed reads and streams, frame-chain resolution, and Zone transforms. |

Generated model types remain in the specification namespaces:

- `Opc.Ua.Rsl`
- `Opc.Ua.Gpos`

The base package exposes generated NodeIds, NodeStates, encodeables, model
loaders, and generated ObjectType clients. The hand-written APIs compose those
generated basics instead of replacing or inheriting from them.

## Minimal standalone server

`AddPositioningServer` owns an RSL/GPOS node manager. Configure the address
space after the generated models are loaded:

```csharp
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Opc.Ua.Positioning.Server;
using Opc.Ua.Positioning.Server.Hosting;

HostApplicationBuilder host = Host.CreateApplicationBuilder(args);

IPositioningServerBuilder positioning = host.Services
    .AddOpcUa()
    .AddServer(options =>
    {
        options.ApplicationName = "PositioningServer";
        options.EndpointUrls.Add(
            "opc.tcp://localhost:4840/PositioningServer");
    })
    .AddPositioningServer();

positioning
    .AddGeoLocationProvider<MyGpsProvider>()
    .AddRelativeSpatialLocationProvider<MyRelativeLocationProvider>()
    .ConfigurePositioningFor<PositioningNodeManager>(async context =>
    {
        PositioningAddressSpaceBuilder model = context.AddressSpace;

        // Create a SpatialObjectsList, SpatialObject AddIns and concrete
        // Cartesian frames, then register each completed subtree.
        // Create Zones and attach GlobalPosition or GlobalLocation Variables
        // in the same callback.

        await ValueTask.CompletedTask;
    });

await host.Build().RunAsync();
```

For a server that already owns the companion address space, keep that manager
as the single namespace owner:

```csharp
IPositioningServerBuilder positioning = serverBuilder
    .AddNodeManager<MyNodeManagerFactory>()
    .AddPositioningFor<MyNodeManager>();

positioning.ConfigurePositioningFor<MyNodeManager>(
    context => ((MyNodeManager)context.Manager)
        .ConfigurePositioningAsync(context));
```

The owning composite manager must load the RSL model before GPOS and advertise
both namespace URIs.

## Server authoring

`PositioningAddressSpaceBuilder` creates instances through the generated
factories and supports:

- `SpatialObjectsListType` AddIns below the standardized
  `RelativeSpatialLocations` entry point.
- `SpatialObjectType` AddIns attached to existing objects through `HasAddIn`.
- Cartesian world, position, attach-point, internal, and alternative frames.
- GPOS `ZoneType` instances defined by ground control points or a
  position/radius.
- `GlobalPositionType` and `GlobalLocationType` Variables attached to tracked
  objects.
- Coherent aggregate/component updates, optional-field status, `NodeVersion`,
  and model-change notifications.

Provider bindings publish an initial value and then consume a cancellation-aware
async stream:

```csharp
PositioningProviderSubscription subscription =
    await model.BindGlobalLocationAsync(
        globalLocation,
        provider,
        sourceId,
        cancellationToken: ct);
```

Dispose the subscription asynchronously during server shutdown. Provider
failures retain the last value, set its status to `BadCommunicationError`, log
the failure through `ITelemetryContext`, and fault `Completion`.

`IGeoLocationProvider` is intentionally technology-neutral, and lives in
`Opc.Ua.Server` (namespace `Opc.Ua`) rather than in a companion-model assembly.
Global Positioning System (GPS) and World Geodetic System 1984 (WGS84)
coordinates are built-in use cases. Real-time location systems (RTLS),
ultra-wideband (UWB), radio-frequency identification (RFID), local
floor-plan coordinates, and other tracking systems can use the same contract.
An RSL provider
is also useful when a robot controller, metrology system, or kinematic service
is authoritative for a relative frame rather than a global coordinate.

Because the contract is shared, **one provider implementation serves every
model that publishes location**. The same instance can back GPOS
`GlobalLocation` Variables here and OPC 10030 (ISA-95) `GeoSpatialLocationType`
Variables — see [ISA-95](ISA95.md#geospatiallocationtype-provider-seam).
A sample can include:

- `GeoPosition` with latitude, longitude, optional height, accuracy, floor,
  and EPSG code
- `GeoOrientation`
- Text labels

```csharp
public sealed class MyGpsProvider : IGeoLocationProvider
{
    public bool SupportsPush => true;

    public ValueTask<GeoLocationSample> ReadAsync(
        string sourceId,
        CancellationToken ct = default)
    {
        return new ValueTask<GeoLocationSample>(
            GeoLocationSample.Good(
                new GeoPosition(47.3769, 8.5417, 408.0, EpsgCode: 4326)));
    }

    public async IAsyncEnumerable<GeoLocationSample> WatchAsync(
        string sourceId,
        [EnumeratorCancellation] CancellationToken ct = default)
    {
        // Yield a sample whenever the receiver reports a new fix.
    }
}
```

Set `SupportsPush` to `false` when the source can only be polled; the binding
layer then never calls `WatchAsync` and reads through `ReadAsync` at the
Variable's sampling interval instead.

A GPOS Variable requires coordinates. If a sample has `Position` set to
`null`, the server rejects it with `BadNoDataAvailable`. If the position's
`EpsgCode` differs from the Variable's configured
`CoordinateReferenceSystem`, the binding fails rather than mis-georeference
the value silently. Set `EpsgCode` to `null` to accept the Variable's
configured coordinate reference system.
`InMemoryGeoLocationProvider` ships as a reference implementation for tests and
for servers whose positions are pushed in from elsewhere. Watching an unknown
source does not create a sample: reads return `BadNotFound` until `Update`
supplies one. `Fault` makes reads surface the supplied exception even for an
unknown source; a subsequent `Update` clears the fault and publishes its sample.

## Client

Register client factories over the managed-session registration:

```csharp
services.AddOpcUa()
    .AddClient(options => { /* endpoint and application options */ })
    .AddPositioningClient();
```

Direct constructors are also available:

```csharp
var rsl = new RelativeSpatialLocationClient(session, telemetry);
var gpos = new GlobalPositioningClient(session, telemetry);

await foreach (PositioningObjectEntry list in
    rsl.EnumerateSpatialObjectListsAsync(ct))
{
    await foreach (PositioningObjectEntry spatialObject in
        rsl.EnumerateSpatialObjectsAsync(list.NodeId, ct))
    {
        RelativeSpatialFrameValue frame =
            await rsl.ReadPositionFrameAsync(spatialObject.NodeId, ct);
    }
}

await foreach (PositioningObjectEntry zone in gpos.EnumerateZonesAsync(ct))
{
    GroundControlPointFitResult transform =
        await gpos.ReadZoneTransformAsync(zone.NodeId, cancellationToken: ct);
}
```

`ResolveFrameToWorldAsync` follows the RSL `Base` chain, composes each
`ThreeDFrame`, and rejects missing nodes, bad status, cycles, and excessive
depth. `ObserveFrameAsync`, `ObservePositionFrameAsync`,
`ObserveNodeVersionAsync`, `ObserveGlobalPositionAsync`, and
`ObserveGlobalLocationAsync` use `IStreamingSubscription`.

GPOS structured types are registered with both the session and message-context
encodeable factories before reads, so binary `ExtensionObject` values decode to
the generated types.

## Transform conventions

RSL uses a right-handed coordinate system:

- `A`: roll about X
- `B`: pitch about Y
- `C`: yaw about Z
- column-vector matrix: `Rz(C) * Ry(B) * Rx(A)`

`RslFrameTransform` supports conversion, composition, inversion, point
transformation, and deterministic gimbal-lock handling.

The built-in coordinate-reference-system transformer supports WGS84 /
EPSG:4326, ECEF, and local East-North-Up coordinates. Inject
`ICoordinateReferenceSystemTransformer` for another CRS.

`GroundControlPointFitter` supports rigid, similarity, and affine fits. When
elevation or rank is insufficient, it selects a horizontal 2D fit. It forces
a proper rotation for rigid and similarity modes, and rejects affine
reflections unless you enable them. The fitter reports residual, determinant,
rank, dimension, and invertibility diagnostics.

## Robot and OpenUSD sample

[`MinimalRobotServer`](../samples/Robotics/MinimalRobotServer) composes RSL and GPOS into
its Robotics node manager. Both robots publish `GlobalLocation` values and
derived local RSL frames. Each robot independently selects `Fixed`,
`FigureEight`, `Circle`, or `Shuttle` motion. RSL position/orientation drive
OpenUSD `double3` transform operators, while GPOS longitude, latitude, and
elevation drive live custom attributes.

The generic OpenUSD connector has no Positioning dependency; it handles core
`ThreeDCartesianCoordinates`, `ThreeDOrientation`, and `ThreeDFrame` values.