Vegetation indices (NDVI, GNDVI, NDRE)
Vegetation indices are calculated values that reflect the condition of the crop (healthy, stressed, weed, diseased). DroneField supports three classical indices: NDVI, GNDVI and NDRE.
All three require a multispectral drone (P4M or M3M). RGB-only drones (P4R, M3E) cannot produce them.
What the indices mean
Section titled “What the indices mean”NDVI — Normalized Difference Vegetation Index
Section titled “NDVI — Normalized Difference Vegetation Index”The classic “how good is the stand” measure. From the NIR (Near Infrared) and Red bands:
NDVI = (NIR - R) / (NIR + R)Range: −1 … +1. Positive values indicate photosynthesis; around 0 indicates bare soil, water or shadow; negative values are rare on ground imagery.
NDVI works best on dense stands. A saturated canopy (>0.85) is no longer differentiated — everything “very green” gets pushed to ~1.0.
GNDVI — Green NDVI
Section titled “GNDVI — Green NDVI”Uses Green instead of Red:
GNDVI = (NIR - G) / (NIR + G)More sensitive to chlorophyll content and nitrogen stress. Better at separating healthy and very-mature plants than NDVI.
NDRE — Normalized Difference Red Edge
Section titled “NDRE — Normalized Difference Red Edge”Uses the Red Edge band instead of Red:
NDRE = (NIR - RE) / (NIR + RE)The most accurate index for mature, dense stands — it does not saturate where NDVI does. The go-to index for precision N fertilisation. Use this on mature corn, wheat or rapeseed.
Video: NDVI or NDRE? Pick the wrong index and dense crops all look “healthy” while problems hide under the canopy:
How they are computed
Section titled “How they are computed”Indices are part of the processing flow:
- Enable Process multispectral images in the Process panel.
- At the end of processing all three indices appear in the
Layers/folder. - The map shows a new NDVI layer (NDVI is active by default; you switch between indices in the side panel).
Vegetation index panel
Section titled “Vegetation index panel”When the NDVI layer is on, a floating panel appears at the bottom-right of the map:
- AI analysis — AI-assisted zoning and a draft spray plan from the Luna assistant (see AI vegetation analysis)
- Index selector — NDVI, GNDVI, NDRE (switches instantly)
- Range — min/max for the visualisation
- Preset ranges — one-click settings
- Colour ramp — legend underneath
- Export — PNG / JPEG / GeoTIFF (QGIS)
- Process — for on-demand index processing (see below)
Preset ranges
Section titled “Preset ranges”The full index range (−1 … +1) is usually too wide for visual interpretation. DroneField offers four one-click presets:
Highlights the small NDVI differences between bare soil and
weeds. Range: roughly 0.05 … 0.30.
Use it for a spring field, to see where weed populations are springing up between rows.
Stress
Section titled “Stress”For detecting stressed canopy (water, nutrient, disease).
Range: roughly 0.30 … 0.65.
Use it for summer rapeseed, corn — where the canopy is already dense but yellowing in places.
Healthy
Section titled “Healthy”Fine-grained view of the mature, healthy canopy. Range:
roughly 0.65 … 0.90.
Use it for dense stands — e.g. pea before flowering — to see where development is faster / slower.
Water / Soil
Section titled “Water / Soil”Focuses on near-zero and negative values. Range:
roughly −0.20 … 0.10.
Use it for standing water detection, bare-soil patches.
Colour ramp
Section titled “Colour ramp”Every preset uses a six-step colour ramp:
| Index value | Colour | Meaning |
|---|---|---|
| Lowest | Dark red | Water, soil, bare |
| Low | Red | Stress |
| Mid-low | Orange | Weak |
| Mid-high | Yellow | Average |
| High | Yellow-green | Healthy |
| Highest | Dark green | Strong, dense |
The ramp maps linearly onto the chosen range. With a range
0.30 … 0.65, 0.475 is yellow.
Custom range
Section titled “Custom range”The panel’s Range slider accepts any min/max. Useful for:
- Centring on a decision threshold (e.g. NDRE 0.40–0.65 = treatment zone for N fertilisation)
- Matching your field’s typical range
Changes take effect immediately — you see the result live on the map.
On-demand index processing
Section titled “On-demand index processing”If you ran processing without the multispectral switch (e.g. quick orthomosaic only), you can request the indices later:
- Click Process in the vegetation index panel.
- The list of missing bands appears (e.g. “NDRE — missing bands: RE, NIR”).
- Click Continue.
- DroneField processes only the missing indices without redoing existing work.
Faster than rerunning the whole processing.
Export
Section titled “Export”The panel’s Export button offers three formats:
PNG / JPEG
Section titled “PNG / JPEG”The visualisation is saved as an image with the chosen colour ramp. No georeference — a simple picture, fine for email or presentations.
GeoTIFF (QGIS)
Section titled “GeoTIFF (QGIS)”The most valuable export. A .tif (GeoTIFF) file:
- Float32 depth — every pixel is the actual index value (e.g.
0.6234) - Georeferenced in WGS84, EPSG:4326
- Loads directly in QGIS, ArcGIS, ENVI and other GIS programs
QGIS auto-detects the projection on import. You can re-render the values with any colour ramp.
See Exporting to QGIS for details.
Exported file names
Section titled “Exported file names”Export/├─ NDVI/│ ├─ ndvi_visualisation.png│ ├─ ndvi_visualisation.jpg│ └─ ndvi_geotiff.tif├─ GNDVI/│ └─ ...└─ NDRE/ └─ ...What not to do
Section titled “What not to do”- Don’t base decisions on NDVI alone — no index tells the whole story. Soil sampling and ground inspection always complement it.
- Don’t compare two different drones — P4M and M3M filter spectra differently; values are not 1:1 comparable.
- Don’t mix morning and afternoon flights within one project — changing solar angle shifts index values.