Environment reference
Runtime configuration is done with environment variables. Set them before
launching ncv.
| Variable | Values | Default | Purpose |
|---|---|---|---|
NCVIEW_THREADS | integer | min(CPUs, 8) | Parallel rasterization threads (RAYON_NUM_THREADS is also honored). The conservative default avoids hogging HPC head-node resources. |
NCVIEW_IMAGE_PROTOCOL | kitty, sixel, iterm2, cells | auto-detected | Override graphics capability detection. Auto-detection identifies iTerm2 from environment hints; Kitty and Sixel are selected only through this override or a positive capability match. An explicit setting is honored as given. |
NCVIEW_SCIENTIFIC_RENDERING | 1 / 0 | 1 (locked) | Keep nearest-neighbor scientific rendering, or allow interpolation (0). |
NCVIEW_IMAGE_FILTER | nearest, lanczos3, catmull-rom, triangle, gaussian | nearest | Image filter when scientific rendering is unlocked. |
NCVIEW_CELL_PIXEL_SIZE | WxH pixels, e.g. 10x20 | from the terminal | Terminal cell size used to size graphics images and map mouse clicks. Set it when the terminal does not report usable pixel dimensions (common over SSH); known 640x480 placeholders and reports under 4x8 pixels per cell are ignored, and 10x20 is assumed. |
NCVIEW_ANONYMOUS_ACCESS | truthy (1, true, yes, on, y) | auto | Force credential-free access for public S3/GCS/Azure objects. Any other value, including 0, leaves the automatic decision in charge rather than forcing signed access. Auto mode uses ambient credentials if present, otherwise a cached metadata-endpoint probe, and selects anonymous access when neither yields credentials. |
NCVIEW_LAND_DETAIL | 110m, 50m, 10m, auto | 110m | Coastline resolution after enabling the b backdrop; auto selects by zoom level. |
NCVIEW_UG_INTERMEDIATE_SPACING_DEG | degrees, 0 < x <= 90 | 0.25 | Cell size of the regular latitude/longitude grid that unstructured-grid fields (currently MPAS) are regridded onto. Smaller values sharpen the map but cost more per read. |
NCVIEW_COLORMAPS | directory | — | Extra directory of .ncmap files for the palette catalog. |
NCVIEW_LIB_DIR | directory | — | Also searched for colormaps, including share/ncview/colormaps. |
NCVIEWBASE | directory | — | Also searched for colormaps, including share/ncview/colormaps. |
NCVIEW_EXPORT_DIR | directory | current directory | Where e writes exports. |
NCVIEW_EXPORT_BACKGROUND | transparent, white | transparent | Export canvas background. |
NCVIEW_EXPORT_TEXT | dark, light | dark | Export text/border color (light for dark slides). |
NCVIEW_EXPORT_FONT | font list | Fira Code, monospace | SVG export font selection (PNG always uses the embedded font). |
NCVIEW_SESSION_DIR | directory | platform default | Where per-dataset session state is stored. |
Notes
- Secrets are never read from arguments; cloud credentials come from ambient
provider configuration (
AWS_*,GOOGLE_*,AZURE_*). NCVIEW_IMAGE_FILTERandi-cycling only take effect whenNCVIEW_SCIENTIFIC_RENDERING=0; the default preserves exact scientific cells.- Malformed
.ncmapfiles discovered via any colormap path are ignored at startup rather than causing an error.