The workspace, piece by piece.

01The example

The series of the Trend test guide: 41 annual Landsat medoid composites of a vegetation index, 1985 to 2025, over the coast of Sergipe and Alagoas in north-eastern Brazil (path/row 215/067), one GeoTIFF per year, 7478 × 7319 pixels in EPSG:4326 at about 30 m. As there, each year is opened through a VRT that declares 0 as no data, in a folder named 215_067, so the layer takes that name. One figure uses the Sentinel-2 series of the STAC guide, for its bands.

The times quoted were measured with Janus' processing threads limited; with all of a machine's cores they are shorter.

02The status bar

A bar along the foot of the window, always in view. On the left, what is under the cursor on the map:

Pixel

col 6804 row 4252: the active layer's pixel, counted from 0 at the top left.

Coordinates

In the layer's CRS (x, y to the centimetre), then in longitude and latitude (WGS 84, six decimals). A layer in degrees, like this one, gives lon and lat once.

Value

What the map shows there: value and the number, class and its name on a class map, the mean or the trend in those display modes, the largest drop's date, the maps of a run over it, the vector feature under the cursor. (approx.) while the value still comes from the overview rather than the file.

Over the place of section 06, in 2025, it reads col 6804 row 4252 | lon -36.583216 lat -10.283509 | value 0.171732 (the pixel's centre; the value is the file's). With the cursor off the map it says Point at the map: its pixel, coordinates and value here. On the right, from the left:

Zoom

zoom 60.0% (detail 1:1): screen pixels per pixel of the layer, and what is drawn (the full-resolution tiles, or the overview and its factor).

Scale

The map's scale on the screen, 1:190 000, at 96 points per inch and rounded to two figures, then the ground a screen point covers, 49.3 m/px. On a layer in degrees the metres are those of a degree of longitude at the latitude of the map's centre.

CRS

The active layer's, EPSG:4326; the pointer over it gives its full name.

Tasks

While something runs in the background (a Zeit tool, a deep learning model, a download, an export): how many, the oldest one's name and a progress bar. A click opens Tools → Tasks (or Exports).

The numbers check out by hand. At 60% the map's centre was at 9.37° S, where a pixel of 0.000269° is 29.6 m wide; 29.6 / 0.6 = 49.3 m per screen point, and 49.3 m divided by a point (0.0254 / 96 m) is 186 000, shown as 1:190 000. At 100% over Penedo (10.28° S, section 06) the bar read 29.5 m/px and 1:110 000.

03Tasks and notices

A tool run on the raster works in the background. When a task ends, a notice comes up at the bottom right, above the status bar: Done, the task's name and how long it took, with Show in Tasks and Open folder. A task that failed says Failed, gives the error and a Log button; an export gives Exports. With Janus in the background, the system is also asked for your attention: the taskbar's icon flashes (on a Mac, the Dock's icon bounces).

Tasks shorter than 3 s end without a notice, unless they fail. A notice goes after 8 s, a failure's after 30 s, or with its ×; four at most are shown, the newest at the bottom.

04The command palette

Ctrl+K (or Ctrl+Shift+P, or View → Command palette) opens one search over what Janus does: the items of every menu, every tool, the display modes, the panels, the open layers (make one active, zoom to it), the Layers panel's commands, and the spectral indices the active layer has the bands for. Each row gives its category and its keys. Type, then ↑ ↓ and Enter, or click; Esc or a click outside closes it.

How it matches

Every word typed must match somewhere: at the start of the name scores most, then at the start of a word in it, then inside a word, then the category, then the description. A short word (six letters or fewer) may also match the name's letters in order: gtc matches Go to coordinate.... Among equal matches, the shorter name first.

Used last first

Without a query, and among matches alike, the twelve commands used last come first (kept in the settings).

Not now

A command that cannot run is listed faint, the reason on hover: Blend: Normal when the layer already is, Paste style before a style was copied, an export before a series is open. Exit and Close all come after any other match, so that Enter on a short query does not close anything.

The commands call the same code as the menus: nothing is a copy that can drift. On a series with bands, the indices of the Awesome Spectral Indices join the list, under the category Index, and picking one shows it on the active layer (the calculator guide has more on them).

05Blend modes, groups, styles

The Layers panel is a table of contents: the series, the maps of the runs and the vector layers in one drawing order, the basemap last. Three things joined it in 1.5.

Blend modes

Beside the active layer's opacity, a list sets how its colours combine with what is under it (the layers below and the basemap). The same list is under Blend in a series' menu, in the palette (Blend: Multiply...), and on the command line (--blend multiply).

Normal

The layer over the others, with its opacity.

Multiply

Darkens by what is under it: the layer's colours tint the imagery, and the imagery's detail shows through.

Screen

Lightens: the opposite of Multiply.

Add

Sums the colours.

Darken, Lighten

Keep the darker or the lighter of the two, channel by channel.

The blending is done by the graphics card's own blending stage, a pipeline per mode, so a mode costs nothing more to draw than Normal.

Groups

Select rows (Ctrl + click adds one, Shift + click a run of them), then Group the N selected in the menu of one of them, or Group the selected layers in the palette. They go next to each other in the drawing order, under a row of their own named Group 1. The group's eye shows or hides them all, its arrow folds them, a click selects them (Delete then closes them), and its menu renames it, selects its layers, moves it to the top or the bottom, ungroups it (the layers stay where they are) or closes its layers. A row dropped on a member, or on the group's row, joins it; Out of its group takes one out.

Files opened together make one series, a date each. To see several of its dates at once, unfold the series and drag a date out of it: it becomes a layer of its own and the series is opened again without it. The series' menu Split into layers does it for every date, in a group named after the series, which closes. The new layers take the series' colours: its colormap, its range as it shows it, its classes' names.

Styles

A row's menu has Style:

Copy style

A series' display mode, each mode's colormap, the ranges set by hand (the others are computed again from the other layer's own values), the stretch per date, the RGB bands, the opacity, the blend mode, and its classes' names, colours and visibility; a vector layer's colour.

Paste style

On the row, or Paste style on the N selected.

Saved styles

A name and Save style keep it in the settings; it is then listed in every row's Style menu, given with a click, deleted with its x.

A style made once for a land-cover legend, or for a run's map of years, then goes on every other layer of the kind with two clicks.

06Go to and saved views

Ctrl+G (View → Go to coordinate...) opens a field that takes a place as you have it:

The decimal, comma, UTM and EPSG lines of the table are the same place, and each took the map to it. As you type, the window says where it lands (lat -10.283333, lon -36.583333 -> pixel (6804, 4251), or that it is off the layer). Enter or Go centres the map there, zoomed in to a pixel per screen point at least, with a mark that fades in 8 s and what you typed beside it; Drop a pin there also adds a pin. From the command line: --goto "10°17'S 36°35'W". Place names are not looked up: a coordinate is needed.

Saved views

View → Saved views: a name and Save view keep the area, the date shown and the layers shown. The area is kept as its centre in longitude and latitude and its width in metres, so a view saved on one layer goes back to the same ground on any other, in any CRS (a layer without a CRS keeps pixels). A click on a saved view goes back to it: the date by its label, the layers by their names when any of them is open. They are kept in the settings, listed in the palette as Saved view: name, and deleted with their x.

07Minimap and lens

Minimap

M (View → Minimap, --minimap): the active layer whole in the map's bottom right corner, 170 points on its longer side, the view as a rectangle on it. A click or a drag on it moves the map there. It is drawn again only when what it shows changes.

Lens

L (View → Lens, or Lens on the swipe's bar, --lens): the swipe (C) as a circle that follows the cursor, instead of a divider. Inside the circle, the swipe's comparison; outside, the map. Alt + wheel changes its size (a radius of 110 points at first, from 24 to 800) without zooming the map.

The comparison is set on the swipe's bar, as for the swipe: another open layer, or the same one at another date (Own date) or in another display mode (Own mode). With a single series open it starts at the date before the one shown.

The lens suits questions about one place: is this patch new, was the stripe there the year before? The swipe suits comparing two halves of the view. L goes back from the lens to the divider, C turns either off.

08Where a result came from

Every run of a Zeit tool, of a deep learning model applied and of the raster calculator writes provenance.json in its folder, next to job.json, job.log and its maps. It holds the tool, the versions of Janus and of Zeit (zeit-core's revision), when the run started, how long it took and how it ended, the series it read (its files, the band, index or expression shown, the quality mask), the scope and the window in pixels, the parameters (with those not at the tool's default named), what else it took (a model's file, the calculator's text), and the files it wrote. Here is the run of section 03, shortened:

{
  "format": 1,
  "kind": "zeit",
  "tool": "ar_trend",
  "tool_name": "AR(1) trend (remotePARTS)",
  "janus": "1.6.0",
  "zeit": "2.0.0",
  "zeit_core": "8cfbdbf5ecb2ab740332584749d26c18b724b24a",
  "started": "2026-10-29 00:00:11 UTC",
  "seconds": 13.4082103,
  "state": "done",
  "series": {
    "name": "215_067",
    "dates": 41, "first": "1985", "last": "2025",
    "width": 7478, "height": 7319, "crs": "EPSG:4326",
    "files": ["215_067\\landsat_medoid_1985.vrt", ... 41 files]
  },
  "scope": "ROI",
  "window": [1000, 500, 1700, 1200],
  "params": {"alpha": 0.05, "gaps": "exact", "harmonics": 0, "min_valid": 4, "time": "year"},
  "changed": [],
  "outputs": [{"name": "Significant slope", "path": "...\\ar_trend_sig_slope.tif"}, ... 8 maps],
  "python": "rerun.py"
}

In the Layers panel, the menu of a run's map (or of a series a run or the calculator wrote) gives:

Provenance...

All of it in a window, the parameters changed from the default in the accent colour.

Run again with these parameters...

The tool's window with the run's parameters and scope. On the same series the scope The run's window is the very window it ran on, even if the ROI has moved or gone since. A deep learning run gets its model and post-processing back, the calculator its text.

Python of the run...

The run's code in the Python history's editor (Tools → Python history keeps every finished run, between sessions; copy it, or save it as a .py or a notebook). For a Zeit tool, rerun.py, written beside the run: it reads the series from its files over the run's window with rasterio, makes the same Zeit call with the same parameters, and writes every map the call returns as a GeoTIFF on the window's grid, in a folder python of the run. It needs numpy, rasterio, xarray and zeit-cdts. Reproject, resample, clip and Rasterize write a rerun.py of GDAL's Python, whose files equal Janus' own; the other tools give the run as data.

Open folder

The run's folder.

The run above has a script of 133 lines; its call is zeit.ar_trend(series, time='year', harmonics=0, gaps='exact', min_valid=4, nodata=None, n_jobs=-1) on the 700 × 700 pixels of the window. Run with Zeit's Python (with n_jobs=2, to use two threads), it wrote 11 maps. The six that match maps of Janus' run (the slope, its p-value, t and standard error, the intercept and the AR(1) rho) were equal to them on all 490 000 pixels, to the last bit.

09Preview on a corner

A Zeit tool's window has Preview under Run (see the figure of section 03): the tool on the ROI (its bounding box) or, without an ROI, on at most 256 × 256 pixels at the centre of the view, before the whole scene. Its maps open as layers named Preview: ..., marked preview in the Layers panel; its window is dashed on the map, labelled Preview... while it runs and preview when done. The next preview replaces it: the earlier one is cancelled if still running, and its maps and folder (under Janus' work folder) are deleted. Closing the tool's window removes its preview.

Auto-preview

Previews again 0.4 s after a parameter changes, when Zeit's estimate for the preview's window is 3 s or less. Under the buttons the window gives that estimate; when the parameters have changed since the preview on the map, it says so.

Then Run

Runs on the scope chosen (Whole image, Visible area, ROI), as before.

10Projects and the last session

File → New project, Open project..., Save project (Ctrl+S), Save project as... and Recent projects (the last ten). A project is a .janus file, JSON with a format number, that keeps:

The layers

The series in their drawing order (their files, the band, index or expression, the quality mask, the date shown, the style, opacity, blend mode and visibility), the vector layers (colour, visibility), the runs' maps (their GeoTIFFs, colours, range, and the run's folder with its provenance), the groups and the active layer.

The work on them

The pins, the ROI (a box or a polygon) and the transect.

The window

The view, the swipe or lens, the map panels, the basemap, the saved views and the season.

Each file is kept both relative to the project's file and absolute, the relative one tried first, so a folder with a project and its data can be moved to another disk or machine and still open. Opening a project opens its layers one at a time, as File → Open would, each with its state; a file not found leaves its layer out with a notice (Project opened without some of its layers), and the rest opens. A .janus file also opens from File → Open, dropped on the window, or from the command line: jn work.janus.

The window's title gives the project's name, with a * when it has changes not saved. New project and Open project... over such changes ask first: Save, Discard or Cancel.

The last session

Closing Janus does not ask anything. The session, changes included, is kept every minute and at exit (last-session.janus beside Janus' other data, %LOCALAPPDATA%\Janus on Windows), and, with Settings → Reopen the last session at start turned on (it is off by default), reopened at the next start when Janus is opened without files: the layers, their styles, the view, as they were.

11Undo

Ctrl+Z undoes the last change to the layers; Ctrl+Shift+Z or Ctrl+Y redoes it. The Edit menu (and the palette) says what: Undo Opacity of 215_067, Undo Close 215_067, Undo Layer order.

A layer closed by mistake comes back by Ctrl+Z in its place, with its files, band, style and date, opened again as a project opens its layers. A slider or a layer dragged is one step, whatever the frames in between: nothing is recorded while a button is held. The last 100 steps are kept; New project and opening a project start the history again. A text field keeps its own Ctrl+Z, and drawing an ROI polygon or a transect its own Backspace for the last vertex.

12Web layers

File → Add web layer... (also the Layers panel's + Add and the palette) adds a layer from a map server: a URL, or a preset (INPE's TerraBrasilis, DETER and PRODES; IBGE's geoservices; an OGC API demo). The service is found from the URL (OGC API - Features, WFS and WMS tried in turn) or chosen; Connect reads its capabilities and lists its layers with their titles, a filter above them (IBGE's server has more than ten thousand), the abstract on hover.

Maps: WMS and WMTS

A map becomes a layer of the drawing order, drawn as the basemap is: tiles of Web Mercator asked for around the view (a WMS GetMap per tile, its box computed by GDAL's WMS driver; a WMTS layer by its tile matrix), warped onto the active layer's grid, transparent where the server draws nothing, at its own opacity, its credit at the bottom of the map and in the exports. A layer with a time dimension shows the server's default time, a time typed, the series' date (the last time listed not after the date shown) or up to the series' date (every time from the first to it: PRODES' yearly deforestation accumulated to the date shown, following the slider). Its row's menu: opacity, time, reload, move, remove. A click on the map asks the WMS layers that answer GetFeatureInfo what is there, at the time they show: the Map info window lists each one's features and their fields (a DETER alert: its class, day, satellite, municipality and area). A WMTS layer is drawn from its image tiles (vector tiles are not drawn).

Features: WFS and OGC API

Features are fetched for the visible area, the ROI, the active layer or the whole layer (the box sent to the server), between two dates of a date field and with an attribute filter (sent to the server when it takes it), paged, up to a cap: when the server has more there, the layer is named (first N) and a notice says so. The fetch is a task of Tools → Tasks, with its progress and Cancel; its GeoPackage, in Janus' cache, opens as a vector layer: its colour, attribute table, an alert as the ROI (Alt+click), the series of every alert, zonal statistics, rasterize, Export as... to keep it. The same request within twelve hours is read from the cache. A project keeps the map layers and the fetched layers' requests: opened again, a GeoPackage no longer there is fetched again.

Against Python

The same requests by Janus, by geopandas.read_file on the same source (GDAL's same drivers), by OWSLib and by requests asking the server's GeoJSON directly (tools/bench_ogc_vs_python.py, the median of three, the network included):

The same features, with the same keys, in all four. Janus and geopandas take the same time: both read the server's capabilities and the layer's description first, then page; a single GeoJSON request is faster when its form is known beforehand. IBGE's server answers the box with a third municipality whose outline does not meet it (the box of its outline does): GDAL keeps the two that do, as the table counts them. A WMS tile of DETER (zoom 10) read as the map reads it and a GetMap of the same box asked for directly: the same 21121 drawn pixels, 0 different, 6.1 and 6.2 s (the server renders each).

13Keys

Help → Shortcuts and usage lists them all, with the map's own keys.

14References

• Ives, A. R., Zhu, L., Wang, F., Zhu, J., Morrow, C. J., Radeloff, V. C. (2021). Statistical inference for trends in spatiotemporal data. Remote Sensing of Environment, 266, 112678. doi:10.1016/j.rse.2021.112678 (the AR(1) trend run in this guide; see the Trend test guide).
• Montero, D., Aybar, C., Mahecha, M. D., Martinuzzi, F., Söchting, M., & Wieneke, S. (2023). A standardized catalogue of spectral indices to advance the use of remote sensing in Earth system research. Scientific Data, 10, 197 (the Awesome Spectral Indices).
• Esri World Imagery basemap: Esri, Vantor, Earthstar Geographics, and the GIS User Community.
• INPE, TerraBrasilis: PRODES and DETER (terrabrasilis.dpi.inpe.br). Assis, L. F. F. G., Ferreira, K. R., Vinhas, L., Maurano, L., Almeida, C., Carvalho, A., Rodrigues, J., Maciel, A., Camargo, C. (2019). TerraBrasilis: a spatial data analytics infrastructure for large-scale thematic mapping. ISPRS International Journal of Geo-Information, 8(11), 513.
• IBGE's geoservices (geoservicos.ibge.gov.br); the OGC's Web Map Service 1.3.0, Web Feature Service 2.0 and API - Features, Part 1: Core.
• Zeit: the library behind the tools of Janus, whose Python rerun.py calls.
• The full reference of the window: docs/usage.md.