Playing back a run¶
A completed Run does more than leave three maximum-value rasters behind. It also writes a playback store: the depth and velocity fields on the model mesh, at every output timestep. The Results menu plays that store back in your browser, so you can watch the flood arrive, pause it, scrub to any moment, and click the mesh to read values at that instant.
Playback is the primary way to look at a Run in Hydrata. The maximum rasters answer "how bad did it get here"; playback answers "what happened, and when".
Opening a run¶
Two routes, both landing in the same place:
- Click Results in the left toolbar.
- Or click View Results on a completed Scenario in the Scenarios panel. That closes the Scenarios panel and opens the Results menu for you.
The Results menu lists one row per Scenario whose most recent completed Run has a playback store. Click a row and the run loads: the mesh downloads, the first frames buffer, and play starts on its own. You do not need a second click.
A Scenario whose Run finished but has no store gets a row that is deliberately not clickable, with a short note saying so: playback exists only for Runs that finished after the feature was introduced. For those Runs, use the downloadable outputs instead (see Exporting Results).
Only one run plays at a time. Loading another row swaps the run, and the close control on the player unloads the current one and frees its memory. Leaving the map unloads it too, so coming back to a map always starts from a clean player.
What you are looking at¶
Playback draws the mesh itself, not a raster. Each vertex carries the values
the solver wrote for the timestep on screen, and the colours are interpolated
across the triangles between them. That is a different surface from the
*_max GeoTIFFs, which are gridded and hold each cell's maximum over the whole
Run, so a reading taken here can differ visibly from the maximum raster at the
same point. Dry ground is drawn as dry ground rather than as a very small depth.
Pick what is coloured with Result quantity:
| Quantity | What it is |
|---|---|
| Depth | Water depth at this timestep, in metres |
| Velocity | Flow speed, in m/s |
| Stage | Water surface elevation (ground plus depth), in metres |
| Depth-integrated velocity (dIV) | Depth multiplied by speed, in m²/s, the usual conveyance and hazard product |
| Flood hazard (H1 to H6) | The AIDR hazard classification, as fixed classes rather than a continuous ramp |
| Froude number | Speed against the shallow-water wave speed: below 1 is subcritical flow, above 1 supercritical |
| Manning shear stress | Bed shear in Pa, from the Manning form |
| Courant number | An approximate stability number, computed from the solver's single global timestep rather than per cell, and labelled approximate in the app for exactly that reason |
The store itself holds only depth and the two velocity components. The other six quantities are formulas evaluated in your browser as each frame renders, so switching between them is instant and needs no new download.
The controls¶
The player is a bar at the bottom of the map. It stays on screen while a run is loaded, whichever menu you have open.
| Control | What it does |
|---|---|
| Play / Pause | Start and stop the clock |
| Timeline position | Scrub to any moment in the Run. The tick labels are model time (seconds, minutes, hours or days), not wall-clock time |
| Playback speed | Whole run in a fixed wall-clock time, real time, or slow motion |
| Result quantity | Which of the eight quantities is coloured |
| Legend | Show the colour legend for the current quantity |
| Inspect | Click the mesh to read values at the current timestep |
| Flow | Velocity arrows over the colour, with adjustable density and scale |
| Trails | Particle trails seeded on the velocity field, with adjustable density and speed exaggeration |
| Wireframe | Overlay the mesh triangle edges, so you can see the resolution you actually built |
| Max | Swap the current timestep for the peak value reached anywhere during the whole Run |
| Display | A drawer holding appearance (result and background opacity), the overlays above, and the colour scale below |
| Close | Unload the run and release the memory it holds |
Max is an envelope, not a moment
With Max on you are looking at the highest value each point reached at any time, so different points on screen are showing different instants. It answers the same question as the maximum rasters. Some stores carry no envelope for the quantity you have selected, and the control says so instead of guessing.
Reading the legend and the colour scale¶
The legend names the quantity and its units, and shows the ramp currently in use. Two things are worth knowing before you compare one run against another:
- You can move the ends of the ramp. Each quantity has a colour scale ceiling and an optional floor. Values under the floor are hidden, which is the tidy way to drop a film of shallow water off the map. A reset control puts back the shipped value, so a changed scale is never permanent.
- The shipped bounds are chosen for flood work, not for the data's range.
Depth and velocity open on the same ends as the maximum-value map layers, with a
shallow floor hiding the thinnest water, so above the floor the player and the
Depth Maxlayer colour a value the same way. Depth-integrated velocity and shear stress are deliberately stretched into the range studies actually read, so those two do not match their raster's colours. - Every run opens on the same bounds, because they are fixed defaults rather than something derived per run. That is what makes two runs comparable by eye, and it is also why a bound you changed is gone when the next run loads.
- A run that exceeds the standard scale says so. Rather than clipping silently, the legend notes that the ramp was extended to this run's maximum.
The legend also carries the tolerance note described above: it reads the smoothed vertex field, not the maximum rasters.
Inspect: values at a point and a time¶
Switch Inspect on and click anywhere on the mesh. The readout gives the values at that point for the timestep on screen, and it is explicit about what it sampled: the smoothed vertex field, not the maximum raster. Click dry ground and it says dry ground; click outside the mesh and it says there is no mesh data there.
Buffering, and what a slow connection does¶
The store streams in chunks while you watch, so the player has honest states for "waiting for data", and none of them mean the model went wrong:
| What you see | What it means |
|---|---|
| Buffering, with a percentage | The first frames are still arriving. Play starts on its own at the end of it |
| Buffering scrub target | You scrubbed somewhere the player has not fetched yet |
| Buffering, waiting for data | The chunks for the next frames have not arrived yet |
| Out of buffered frames, waiting for the connection | The stream fell behind. Playback resumes on its own when frames arrive |
| Paced, with a multiplier | The connection cannot keep up with the speed you chose, so playback is running slower on purpose. Your selected speed comes back on its own once the buffer recovers |
All five are network conditions. A Run that failed never reaches the player at all: it stops at Error in the Scenarios panel, where the failure message lives. See Troubleshooting.
A run left open for a long time is fine too. The links the player streams through are time limited, and when they lapse the player fetches fresh ones and carries on.
When a device cannot play a run¶
Before a single frame is downloaded, the player checks the run's declared size against the memory it can expect on this device. A mesh too large for the device is not attempted: instead of failing halfway through a large download, the player shows the Run's maximum-depth layer and says playback is unavailable on this device. A phone opening a large public model therefore still sees the flood extent, which is usually the question a visitor came with.
If a run will not play on a laptop that ought to manage it, close other tabs and try again: the budget is computed from what the browser reports at the moment the run is opened.
What a visitor to a public project sees¶
A Public project is reachable by its link, and playback is part of what a visitor gets: the Results menu, the player, the legend and Inspect, all read-only. Nothing needs to be signed in, and nothing needs to be installed.
The public Msimbazi River Demo project is the worked example: hydrata.com/catalogue/#/map/6755. Open it, click Results, and pick a Scenario.
A visitor holding no role on the project is deliberately shown less than a member. They get the Run's identity, its status, its mesh size and its two time axes, plus the result layers the map needs. They do not get the Run's price, the download links, the run log, the raw failure text, or the names of the people who built the model. The inputs side of the project stays read-only for them as well: there is no Build and no Run.
See Sharing your project for how visibility, members and the project link fit together.
Related pages¶
- Viewing Results for the result layers, the cross-section tool and how to compare two Scenarios
- Exporting Results for the downloadable GeoTIFFs, the SWW time series and the scenario package
- Sharing your project for who can open a project and what they see
- ANUGA Concepts for the physical meaning of depth, velocity, stage and momentum