FieldglassView and render GRIB1, GRIB2, NetCDF and Zarr weather data in VS Code Installation Launch VS Code Quick Open ( Ctrl+P), paste the following command, and press enter.Copied to clipboard |
FieldglassOpen a GRIB or NetCDF file, or a Zarr store, in Visual Studio Code and see what's in it: every message listed with its parameter, level and time, and any field drawn as a map you can reproject, probe and contour. There's nothing else to install. You don't need Python, C libraries or a compiler, because the extension ships a prebuilt binary for your platform. Every decoder is written from scratch in Rust, which is what makes that possible. It decodes every GRIB2 packing the WMO defines and turns spherical-harmonic (spectral) fields back into a map.
Getting startedOpen any file ending in A file with another name can still be opened. Right-click it in the Explorer, choose Open With…, and pick Fieldglass Viewer. If it isn't a format Fieldglass reads, you get a hex and text view of its bytes instead. A Zarr store is a folder rather than a file, so it opens a different way. Run Fieldglass: Open Zarr Store… from the Command Palette and pick the folder. It opens straight into the render panel. What it opensGRIB1 and GRIB2GRIB is the format forecast centers share model output in. Fieldglass lists every message's metadata and draws any field it can decode as a color image. GRIB2 decodes every packing the WMO has defined, and the GRIB2 packing modes table lists them. Some fields, called spectral fields, store waves instead of values on a grid. Fieldglass turns global ones (spherical harmonics) back into a map and draws them. The map is half a degree, which shows detail up to T359, so a finer field is drawn at T359 and the panel says so ("shown at T359 of T1279"). Clicking a point shows both the value on the map and the field's full-detail value there. Limited-area spectral fields (bi-Fourier) aren't drawn yet. Two messages can be drawn together as wind or current arrows. NetCDFFieldglass shows the full structure of both classic and NetCDF-4 (HDF5) files: their dimensions, variables and attributes. Pick a variable and two axes to draw, then step through the rest, such as time or level, or play them as an animation. Click a cell to plot the variable through it as a time series, profile or transect, or pick two axes that aren't latitude and longitude for a cross-section. Grids with ordinary latitude and longitude axes work, and so do WRF and GOES files, and ocean or satellite files that give a position for every cell. ZarrFieldglass opens v2 and v3 stores. A store is drawn exactly as NetCDF is, with the same slice picker, animation, line plots, projections and overlays, and only the chunks a slice covers are read. What works whereSome things work the same way for every format. The three file formats, GRIB1, GRIB2 and NetCDF, open from the file types listed above or through Open With… for any other file, and are recognized from their first bytes either way. A Zarr store opens from the Command Palette instead. For every format, the render panel has the colormap picker (eight maps, each reversible, plus any GMT color tables you import), linear and log10 color scaling, the point probe, zoom and pan, and PNG export. The table covers the rest, where the formats differ. A bare tick means a feature works in full, and a tick followed by text means it works within the limit given. Where a format has no entry, the feature doesn't apply to it.
Legend: ✅ supported, and any text after it names the scope · ❌ not available · n/a doesn't apply to the format. The render panelThe render panel is where a field becomes a map. Each of the controls below works the same way whichever format the field came from, except where it says otherwise. ProjectionsThe projection picker offers eight targets. Source draws the grid in its own shape. The others are equirectangular, Web Mercator, orthographic, polar stereographic, and three whole-world maps: Mollweide, Robinson and Equal Earth. Most of them take a center you choose. Orthographic recenters on any longitude and latitude, polar stereographic takes either pole with any central meridian, and the three world maps take a central meridian. These grids reproject into every target:
Spherical-harmonic fields from either GRIB edition, and GRIB2 HEALPix fields, are turned into a latitude and longitude grid first, so they reproject too. Zoom and panOn the equirectangular and Web Mercator maps, scroll over the map to zoom around the pointer, and drag to pan, including across the date line. The image follows the gesture straight away and is redrawn at full detail when you let go. The Bounds row gains zoom in, zoom out and Reset view buttons, and each gesture writes the new window into its latitude and longitude fields, so you can finish by typing an exact one. A click without a drag still reads the value under the pointer. ColorsThere are eight colormaps: five sequential (viridis, plasma, cividis, turbo and grayscale) and three diverging (red–blue, brown–teal and cool–warm), and each can be reversed. Viridis is the default. Diverging maps suit anomaly and difference fields, where the middle value is the one that matters. The colors are applied in Rust, and the legend is drawn from the same table that paints the grid. The Log₁₀ toggle switches from linear scaling to base-10 log. It spreads a field that spans orders of magnitude, such as precipitation, aerosol optical depth or chlorophyll, evenly across the colors. Values of zero or below are drawn as missing, and the toggle is grayed out unless the color range's minimum is above zero. Your own color tablesFieldglass: Import Color Table… in the Command Palette reads a GMT color
palette table ( A table that uses another color model (HSV or CMYK), transparency, pattern fills, or one key and color per line is refused, with the line it failed on, and nothing is imported. Wind and current arrowsA GRIB file stores a wind or current as two messages, one for each direction. The field you opened is one component, and the Vectors row picks the other. Tick Arrows and choose the v component, and the arrows are drawn over the map in the color and weight the other overlays use. You can set the spacing, or let it fit about twenty-four arrows across the grid. An arrow's length on screen depends only on its speed, so two equal speeds draw equal arrows anywhere on any map. The arrow for the fastest flow is about as long as the gap between arrows, up to a quarter of the map's shorter side, so when you zoom in the arrows spread apart and keep their heads. A key in the corner is an arrow labeled with a speed in the field's own units, and it goes into an exported PNG with the arrows. Each arrow points the way the flow runs on the map, so on an orthographic globe or a polar view the arrows turn with it. Some files, including HRRR, NAM and Canada's polar-stereographic winds, give their components along the grid's axes rather than east and north. Those are turned through the grid's own north, and the panel says so. It also says when the two messages aren't a u and v pair, such as wind speed with wind direction, or are a pair picked the wrong way round, though it still draws the arrows. A cell missing either component draws no arrow. Cross-sectionsThe slice picker's X and Y selectors take any two of a variable's dimensions. So a time–latitude Hovmöller diagram, a latitude–depth section or a time–level plot is a matter of picking the axes. A pair that isn't the file's own latitude and longitude isn't a map, since nothing places it on the Earth. The panel says so, puts away the projection picker and the map overlays, and labels the axes from their own coordinates instead: a CF time as a date (or, on a calendar other than the standard one, its value with its units), and everything else as its value with units. Files that hold nothing but cross-sections, such as a moored time series of depth against time, draw the same way. AnimationA NetCDF or Zarr panel with a dimension to step through, such as time, shows
an Animate row. It has first, back, play and pause, forward and last, a speed
from half a step to ten steps a second, and a Loop toggle. It starts on the
time axis, which it finds from the file's CF metadata ( While it plays on an automatic color range, every frame is colored on the range of the frame you started from, so a color means the same value in every frame. A start frame with the same value in every cell has no range to hold, so then each frame sets its own. Each step waits for the one before it to finish drawing, so a slow file plays slower rather than falling behind. Moving a slice slider by hand stops playback. Each slice stepper shows the coordinate at its index beside the number, such as 500 millibar or a date, and so does the Animate label. The line under the heading names the slice drawn, so an exported PNG says which one it is. Line plotsIn a NetCDF or Zarr panel, tick Line plot, and a click that reads the value under the pointer also draws a line plot below the readout. It shows the variable through that cell along an axis you choose: a time series, a vertical profile or a transect. The box starts unticked, so a click only reads the value until you ask for the plot. Points are placed by the axis's own coordinates and labeled with their units, gaps stay gaps, and a dashed line marks the slice on screen. Only the chunks the line crosses are read. Zonal averageThe Zonal average checkbox draws the field's mean along each row of latitude as a line below the map. It works for regular latitude and longitude, Gaussian, Mercator and reduced grids in any format. On a reduced grid only the values each row stores are averaged, and a row with no data is a gap. Rotated and projected grids have no rows of latitude, so there the checkbox is hidden, and the "Not available for this grid" line under the grid caption says why. Comparing two fieldsThe Compare row picks a second field and an operation: A − B, B − A, A + B, mean(A, B), or A / B. A difference map is the classic way to read an anomaly, a bias, or the change between two time steps. For GRIB, the second field is another message in the file. For NetCDF and Zarr, it's the same variable at a second slice, with its own dimension steppers. A cell missing in either field is missing in the result, and the two fields must be on the same grid. The result is drawn like any other field, so the projection, overlays, colors and scaling all apply. Reading a valueClick anywhere on a field to read the point under the pointer, with the decoded value and its units there. The readout uses the same pixel-to-point mapping as the picture, so the number is exactly the one the color shows, on every projection. A click off the globe reports nothing. Contour linesThe Contours toggle draws lines of equal value over the field, and they follow the map through every projection. Fieldglass picks round levels (1, 2 or 5 times a power of ten), or you can set an interval. Lines break cleanly around missing data. A "contours only" mode hides the colors so the lines read on a blank background. The lines are traced on the grid and then placed through the same mapping the picture uses, so they line up with the data. Contours work on the latitude and longitude family (regular, Mercator, rotated, regular and reduced Gaussian, and reduced latitude and longitude) and on the projected grids (Lambert conformal, polar stereographic, transverse Mercator and Lambert azimuthal equal-area). On a geostationary scan-angle grid the panel says contours aren't available, instead of drawing them wrong. Map overlaysFive layers can be drawn over any field: coastlines, country borders, lakes, rivers, and a latitude and longitude grid. Each one is toggled on its own and has its own color and line weight, so you can tell a coastline from a border at a glance. The four map layers are Natural Earth 1:110m data, bundled with the extension, so nothing is fetched while you work. They're projected in Rust through the same mapping as the field, so an overlay can never drift from the picture under it. LimitsFieldglass is a viewer, and it doesn't edit a file's metadata. The Rust library can patch a GRIB1 message's forecast period byte by byte, but the viewer doesn't offer it. The extension reads a whole file into memory, so that remote and virtual workspaces keep working. That makes archives of several gigabytes a poor fit. A Zarr store is the exception, because it's read one document or chunk at a time. A few formats and grids fall outside what's drawn:
Lambert and polar-stereographic grids are placed on the Earth shape the file declares, which matches an independent decode point for point for the spherical shapes nearly all data uses. A grid that declares an oblate spheroid is projected on that spheroid's mean radius instead, which is within about 0.1%. Transverse Mercator and Lambert azimuthal equal-area are the exceptions: they run on the declared spheroid, because the mean radius would place a UK-area field about 2.8 km out and a European one about 13.5 km out. InstallingSearch for "Fieldglass" in the Extensions view and install it from the Marketplace. To install a particular release by hand, download the
Then run Extensions: Install from VSIX… from the Command Palette and pick the file, or install it from a terminal: Reload the VS Code window when it's done. Fieldglass needs VS Code 1.85 or newer. AttributionThe bundled colormaps are third-party color specifications, used under their own terms:
The GRIB code tables are third-party data too. The WMO parameter, surface,
time-range, center and constituent names are from the WMO's The coastline, border, lake and river overlays are Natural Earth 1:110m data, which is in the public domain. MoreFieldglass is open source, under MIT or Apache-2.0 at your option. The project page has the Rust crates and the browser package the extension is built on, the changelog, the roadmap, and the place to report a problem. AI disclosureMuch of this project's code, tests and documentation was written with AI assistance (Anthropic's Claude), under the maintainer's direction and review. How do I maintain quality?I treat the AI as a fast contributor whose work I don't take on trust:
Where do I currently notice gaps?
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