23. Replaying estimated states¶

Once the estimated-state lake holds a day (ch. 22), the desktop app and the web console can replay it: the GB network on the map, one reconstructed state per 30-minute settlement period, each state fitted to that period's real telemetry. This chapter covers how to start a replay, what the three bridge pickers do, how to read the chi-square status pill that accompanies every estimated frame, and what the web console shows. The apps get their frames from the GDA bridge server, which ch. 24 covers.

Before you start¶

A reachable bridge. The apps are clients. A bridge server with the estimated lake behind it must be running and reachable, on your own machine or on a server you have access to (ch. 24).
An endpoint in the app settings. The desktop app lists a Live bridge model source when BridgeEndpoint in %LOCALAPPDATA%\GridSim\settings.json is non-empty. The default is empty, so a fresh install does not list Live bridge and connects to no bridge: set the endpoint first. The web console shows its bridge cards when the GridSim:BridgeEndpoint configuration key is set. For a bridge on your own machine set the value to ws://127.0.0.1:8770/ws/bridge and allow the unencrypted address (BridgeAllowUnencrypted, below). Ch. 3, Configuration lists both settings.
An estimated lake for the network you pick. The estimated lake is built on gb-spine (the 316-bus GSP-level network). Pick gb-spine for estimated replay. Any other network has no estimated lake, and the stream falls back to a live solve (see Pitfalls).
Days that were estimated. An estimated replay contains only the settlement periods the lake holds.

Worked example¶

Start the desktop app on the estimated source of gb-spine, anchored 60 days back:

dotnet run --project src/GridSim.Wpf -c Release -- "Live bridge" --zone gb-spine --back 60 --bridge-source estimated

The non-flag argument "Live bridge" boots the app straight onto the bridge source. --zone, --back and --bridge-source set the ZONE, FROM and SRC pickers before it connects. The app connects and sends one start action for gb-spine with source estimated, a start of now minus 60 days and 2 frames per second, and the server answers.

The reference lake holds one stored period, 2026-09-01 11:00 UTC. A stored-lake stream plays the periods at or after its start, up to the cutoff and at most 35 days from the start, so a preset shows that period only when it falls in the window. On 2026-10-03, the day of the captures, 60 days ago starts on 2026-08-04 and its window ends on 2026-09-08, so it reaches the period. Every other FROM preset starts after the period, finds no stored frame and gets a live solve instead (see Pitfalls).

The conversation below is the same action driven with a short socket client that prints what the app receives (the client is listed in ch. 24). It uses an explicit start of 2026-09-01 10:00 UTC, the day the example lake was built for, and 144 frames per second so that the stream finishes at once:

$ python bridge_probe.py '{"action":"start","case":"gb-spine","start":"2026-09-01T10:00:00Z","fps":144,"source":"estimated"}' 3
info      {"message": "GridSim-Bridge connected", "cases": ["gb-full", "gb-spine", "zone-enwl", "zone-nged", "zone-npg", "zone-spen", "zone-ssen", "zone-ukpn"]}
topology  case=gb-spine  buses=316  branches=579
info      {"message": "Replaying gb-spine from estimated lake: 1 stored frames 2026-09-01T11:00:00+00:00 -> 2026-09-01T11:00:00+00:00 at 144 FPS"}
state     t=2026-09-01T11:00:00+00:00  source=estimated  buses=316
          estimate={"objectiveJ": 225.414916686831, "chiThreshold": 359.5207249007415, "dof": 317, "measurementsN": 948, "removedN": 0, "iterations": 8, "chiPassed": true}
done      {"framesSent": 1, "source": "estimated"}
[exit 0]

The reference lake holds one estimated period, so the stream is one frame. The app draws the 316-bus topology once, paints the frame's bus voltages and line flows, and reads the estimate block into the pill:

ESTIMATED  *  gb-spine  *  chi-square PASS  *  J=225.4  n=948

J 225.4 sits below the chi-square threshold of 359.5 for 317 degrees of freedom, so the pill is green. Nothing was removed, so no removed= item appears. The stored period was estimated on an earlier build, which counted the prior-solved rows of a --prior solve run in J and in the degrees of freedom; a period estimated by the current build has far fewer degrees of freedom and a different threshold (ch. 22).

Reading the output¶

The three pickers¶

In bridge mode the transport bar shows three pickers. Changing any of them stops the stream and starts a new one on the same connection; nothing reconnects. The pill shows RESTARTING while the new stream starts.

Picker	Choices	Default	What it sets
ZONE	`NGED - Midlands/SW/S.Wales`, `UKPN - London/South East/East`, `SSEN - N.Scotland/Southern`, `SPEN - Scotland/Merseyside`, `NPg - North East/Yorkshire`, `ENWL - North West` (the six DNO zone cases), `GB full`, `GB spine - GSP-level`	`NGED - Midlands/SW/S.Wales`	The network the server streams: `zone-nged`, `zone-ukpn`, `zone-ssen`, `zone-spen`, `zone-npg`, `zone-enwl`, `gb-full` or `gb-spine`
FROM	9 days ago, 12 days ago, 2 weeks ago, 3 weeks ago, 30 days ago, 60 days ago	9 days ago	The instant the stream starts: now minus the preset, computed when the stream starts
SRC	`PRESOLVED`, `ESTIMATED`, `LIVE`	`PRESOLVED`	The reconstruction that plays

The three sources:

PRESOLVED replays the presolved lake: a demand-scaled re-solve of each period. Per-bus state varies from frame to frame.
ESTIMATED replays the estimated lake. Every frame was fitted to that period's real telemetry and carries its fit quality.
LIVE solves the network once and moves only the system scalars (frequency, inertia, demand) from tick to tick.

Every FROM preset is older than the 169-hour no-forward-inference horizon, so the server never rejects a desktop start. A stored source (PRESOLVED, ESTIMATED) runs forward from the start to the horizon cutoff, one settlement period per frame, at 2 frames per second, and one stream covers at most 35 days. LIVE has no 35-day cap: it runs from the next half hour at or after the start to the earlier of the cutoff and the newest reconstructed scalar record, and when the start is later than that record the server moves the start to 7 days before the record and sends an info message (ch. 24). For a stored source, the table gives how many frames a preset produces, to within one period, if the lake holds every period in the window:

FROM	Window to the cutoff	Periods	Playing time at 2 frames/s
9 days ago	47 h	94	47 s
12 days ago	119 h	238	119 s
2 weeks ago	167 h	334	167 s
3 weeks ago	335 h	670	335 s
30 days ago	551 h	1,102	551 s
60 days ago	35 days (cap)	1,680	840 s

The reference lake holds one estimated period, so ESTIMATED produces 1 frame from 60 days ago on the capture date and a live solve from every other preset.

The chi-square status pill¶

The pill sits on the transport bar. In estimated replay it is rebuilt from every frame's estimate block:

ESTIMATED  *  <case>  *  chi-square PASS|FAIL  *  J=<J>  n=<measurements>  [removed=<count>]

chi-square PASS or FAIL. Whether that period's fit is consistent with the uncertainties its measurements declared. The pill is green on PASS and red on FAIL. A FAIL frame is still drawn; its numbers are uncorroborated until you know why the test failed (ch. 21).
J is the weighted sum of squared residuals, to one decimal place, the statistic the test judges. The threshold it is judged against (chiThreshold) and the degrees of freedom (dof) travel in the frame but are not on the pill.
n is how many measurements the fit consumed.
removed is how many measurements the bad-data pass removed in that period. It is omitted when zero. A measurement removed at the same bus period after period is a measurement or model defect, which the closure report's outlier league ranks (ch. 22).

The pill takes other forms around the stream:

Pill text	Colour	Meaning
`CONNECTING * <case>`	amber	The socket is opening.
`LIVE * streaming <case>`	green	Frames are arriving. On `PRESOLVED` and `LIVE` this is the steady state. On `ESTIMATED` it shows only until a frame with a quality block arrives, or throughout if none does.
`ESTIMATED * ...`	green or red	An estimated frame, as above.
`RESTARTING * <case>`	amber	A picker changed.
`QUERY * <op> ...`, `WHAT-IF * <verdict>`	amber	An on-demand query is running or its result is on the map (ch. 24).
`CONNECT FAILED * <message>`, `RESTART FAILED * <message>`, `QUERY FAILED * <op>: <message>`	red	The connection, the new stream or the query failed.
`BRIDGE FAULT * disconnected`	red	The server sent an `error` or the socket dropped.
`HORIZON REJECTION * stream stopped`	red	The client refused a tick newer than now minus 169 hours. The connection's receive loop has ended.

The server's message for a fault is written to the app's event log.

What a frame carries¶

Each state frame carries the slim result (bus voltage magnitude and angle, injections, line flows), the system scalars (frequency, rate of change of frequency, generation, demand, inertia, condition index, RoCoF headroom), the map overlays (branch stress, bus condition), the operator and market series for that period, the source tag and, on an estimated frame, the estimate block. In the example, buses=316 is the bus count of the result block.

Variations¶

Launch straight into a replay. The first launch argument that does not start with - is the model text, and the app opens on the first model source whose label contains it. Put the model text before any flag: a flag's value (gb-spine after --zone) also starts without a dash, so without model text it is matched as model text. When no label contains the model text, the app opens on the first model source, not the last-used one. --zone matches a case name as a substring in the picker's order (--zone nged selects zone-nged; --zone gb selects gb-full because it comes first, so use gb-spine in full). --back N takes 9, 12, 14, 21, 30 or 60; any other value leaves the default of 9. --bridge-source takes presolved, estimated or live.

Switch source mid-stream. Change SRC from PRESOLVED to ESTIMATED on the same zone and start to compare the two routes frame by frame. The divergence product (ch. 22) quantifies the gap per period.

The web console. Configure GridSim:BridgeEndpoint (for example the environment variable GridSim__BridgeEndpoint=ws://127.0.0.1:8770/ws/bridge with GridSim__BridgeAllowUnencrypted=true), start the web app, and the home screen shows two bridge cards. The Estimated bridge card opens:

/dashboard/bridge:gb-spine@estimated

The address is bridge:<case>[@<source>]. The source is presolved (the default when @source is omitted), estimated, live, solves or raw; an unrecognised suffix falls back to presolved, and an empty case means gb-full. /dashboard/live-bridge opens gb-full on the presolved source; its card reads GDA lake: presolved states (gb-full) (it read "live stream" until October 2026). On an estimated stream the header shows a quality pill with the desktop pill's text, for example ESTIMATED: chi-square PASS * J=41.3 n=120, green on a pass and red on a fail. The web console has no pickers. A stored source (presolved, estimated, solves) plays from the case's earliest stored frame, wraps at the end of the window and starts playing on connect. A case with no stored frame gets an info message and no stream; there is no fallback to a live solve. The live source starts 169 hours plus 2 days before now and waits for Play.

Chart the lake's quality series. The GDA repository's DataExplorer (python DataExplorer/server.py, then http://localhost:8077; --port changes it) has a State estimation group with two charts, each defaulting to the last 7 days: Estimation quality (gb-spine) plots objective J against the chi-square gate on the left axis and iterations and removals on the right, and Solve vs estimate divergence (gb-spine) plots the largest voltage, angle and flow differences between the two routes. J above the gate is an inconsistent fit.

Pitfalls¶

ESTIMATED is selected and the pill says LIVE. The case has no estimated lake, or the lake holds no frame in the window. The server answers with an info message and streams a live solve instead, for example No estimated lake for 'zone-nged'; streaming the live on-demand solve instead. The desktop app does not show info messages, so the only sign is the missing chi-square pill. Choose GB spine - GSP-level, or a FROM preset that falls on an estimated day. On the reference lake only 60 days ago does.
The stream is one frame long, or empty. The estimated lake holds the periods that were built. A FROM anchor at or before a stored period replays from the anchor to the cutoff or the end of the 35-day window; an anchor after every stored period finds no frame and falls back to a live solve. The example lake holds one frame.
The pill turns red and the stream stops. HORIZON REJECTION means the client refused a tick newer than now minus 169 hours (against its own clock). The receive loop has ended, so a picker change does not revive it; select another model source and then Live bridge again to open a new connection. BRIDGE FAULT * disconnected means the server sent an error or the socket closed, and the event log carries the message, for example Bridge fault: The bridge closed the connection. After a server error the connection is still open, and a picker change starts a new stream; after a closed socket, reselect Live bridge.
A PASS is not a plausibility check. The chi-square verdict says the fit agrees with the declared sigmas. Read the voltages on the map beside it: a state can pass with a bus voltage well outside the operating band (ch. 22).
--zone picked the wrong network. The match is a substring against the case names in the picker's order.
Right-click does not trip a generator. In bridge mode a right-click on a bus or branch opens the on-demand physics menu, not the local trip (ch. 24). A right-click that hits no bus or branch opens nothing unless a what-if result is showing.

Limits¶

The web console streams estimated states but shows no fit-quality block, so it has no chi-square pill.
The desktop pill shows the verdict, J, n and the removal count. The chi-square threshold, the degrees of freedom and the list of removed measurements are in the frame and are not displayed.
The estimated lake covers gb-spine only, and only days that were built.
The desktop FROM picker has six presets and no date field, and a stored-lake stream is capped at 35 days.
The desktop app has no scrubber in bridge mode; a different start needs a different FROM preset.
After HORIZON REJECTION the desktop app does not reconnect; a new connection needs the model source reselected.
On ESTIMATED, the next estimated frame replaces the QUERY or WHAT-IF pill while the what-if result stays on the map.