🧮 Band Math Expressions#

localtileserver supports on-the-fly band math expressions, enabling you to compute derived imagery like vegetation indices (NDVI), normalized difference water indices (NDWI), and custom band combinations without pre-processing your raster data.

Expressions use the syntax from rio-tiler where bands are referenced as b1, b2, b3, etc. (1-indexed).

Basic Usage#

Use the expression parameter with get_leaflet_tile_layer() or the TileClient methods:

from localtileserver import TileClient, get_leaflet_tile_layer, examples
from ipyleaflet import Map

client = examples.get_landsat()

# NDVI: (NIR - Red) / (NIR + Red)
# Landsat bands: b4 = NIR, b3 = Red
t = get_leaflet_tile_layer(client,
                           expression='(b4-b3)/(b4+b3)',
                           vmin=-0.5, vmax=0.5,
                           colormap='rdylgn')

m = Map(center=client.center(), zoom=client.default_zoom)
m.add(t)
m

We can also view expression results as a thumbnail:

client.thumbnail(expression='(b4-b3)/(b4+b3)', colormap='rdylgn',
                 vmin=-0.5, vmax=0.5)

Common Expressions#

Here are some frequently used band math expressions for Landsat-style imagery:

Index	Expression	Description
NDVI	`(b4-b3)/(b4+b3)`	Normalized Difference Vegetation Index
NDWI	`(b3-b4)/(b3+b4)`	Normalized Difference Water Index
EVI	`2.5(b4-b3)/(b4+6b3-7.5*b1+1)`	Enhanced Vegetation Index
Simple Ratio	`b4/b3`	NIR/Red ratio
Brightness	`(b1+b2+b3)/3`	Average visible brightness

Note

Band numbering is 1-indexed and corresponds to the band order in the source raster file. Check your file’s metadata to identify which bands correspond to which wavelengths.

REST API#

Expressions can also be used via the REST API:

# Tile with NDVI expression
GET /api/tiles/{z}/{x}/{y}.png?filename=multispectral.tif&expression=(b4-b1)/(b4+b1)&vmin=-1&vmax=1&colormap=RdYlGn

# Thumbnail with expression
GET /api/thumbnail.png?filename=multispectral.tif&expression=(b4-b1)/(b4+b1)

Note

When using expression, the indexes parameter is ignored. They are mutually exclusive: use one or the other.