geoskill-map-algebra-calculator

Evaluate band math expressions like NDVI on rasters with a safe expression parser

地图代数计算器 | Map Algebra Calculator

Perform map algebra on multiband rasters using a safe expression evaluator based on Python ast, supporting band references b1..bN, arithmetic, powers and common math functions, with built-in presets for NDVI/NDWI/SAVI/EVI and other indices.

Expressions are validated against a whitelist: attribute access, imports and non-whitelisted calls are rejected; division by zero is automatically set to 0, so the results contain no inf/nan.

Core Algorithm / 核心算法

ast.parse(mode='eval') → whitelisted recursive evaluation (numbers/bands/pi,e/whitelisted functions/+-*/% **) → division-by-zero set to 0 → float32 raster.

Dependencies / 依赖

bash

pip install numpy rasterio scipy matplotlib geopandas shapely pillow

Usage / 使用方法

Example 1 (synthetic data, offline)

bash

python geoskill-map-algebra-calculator.py --bbox 116.0 39.0 117.0 40.0 --synthetic --output-dir ./out

Example 2 (custom expression)

bash

python geoskill-map-algebra-calculator.py --input scene.tif --expr "(b4-b3)/(b4+b3)"

Example 3 (NDWI preset)

bash

python geoskill-map-algebra-calculator.py --input scene.tif --preset ndwi --green 2 --nir 4

Example 4 (ratio + scaling)

bash

python geoskill-map-algebra-calculator.py --input scene.tif --expr "b2/b1 * 100"

Example 5 (synthetic NDVI)

bash

python geoskill-map-algebra-calculator.py --bbox 116 39 117 40 --synthetic --preset ndvi

Output / 输出

File	Format	Description
result.tif	GeoTIFF	Result raster of the operation (main/verifiable deliverable)
expression_meta.json	JSON	Expression and result statistics

Each run also produces output-manifest.json (run manifest).

Data Source / 数据源 / Source

Local GeoTIFF / vector files; --synthetic mode generates physically consistent simulated data, fully offline.

Privacy / 隐私声明 / Privacy

• Runs offline by default; --synthetic mode requires no network at all.
• All processing is performed locally; no user data is uploaded.

License / License

MIT

---

---

name: geoskill-map-algebra-calculator description: 'Evaluate band math expressions like NDVI on rasters with a safe expression parser'

地图代数计算器 | Map Algebra Calculator

对多波段栅格做地图代数运算，用基于 Python ast 的安全表达式求值器支持波段引用 b1..bN、四则运算、幂与常用数学函数，内置 NDVI/NDWI/SAVI/EVI 等预设指数。

表达式经白名单校验，拒绝属性访问、导入与非白名单调用；除零自动置 0，结果无 inf/nan。

核心算法

ast.parse(mode='eval') → 白名单递归求值（数字/波段/pi,e/白名单函数/+-*/% **) → 除零置 0 → float32 栅格。

依赖

bash

pip install numpy rasterio scipy matplotlib geopandas shapely pillow

使用方法

示例 1（合成数据，离线）

bash

python geoskill-map-algebra-calculator.py --bbox 116.0 39.0 117.0 40.0 --synthetic --output-dir ./out

示例 2（自定义表达式）

bash

python geoskill-map-algebra-calculator.py --input scene.tif --expr "(b4-b3)/(b4+b3)"

示例 3（NDWI 预设）

bash

python geoskill-map-algebra-calculator.py --input scene.tif --preset ndwi --green 2 --nir 4

示例 4（比值 + 缩放）

bash

python geoskill-map-algebra-calculator.py --input scene.tif --expr "b2/b1 * 100"

示例 5（合成 NDVI）

bash

python geoskill-map-algebra-calculator.py --bbox 116 39 117 40 --synthetic --preset ndvi

输出

文件	格式	说明
result.tif	GeoTIFF	运算结果栅格（主产物/可验证产物）
expression_meta.json	JSON	表达式与结果统计

每次运行还会产出 output-manifest.json（运行清单）。

数据源 / Source

本地 GeoTIFF / 矢量文件；--synthetic 模式生成物理一致的模拟数据，完全离线。

隐私声明 / Privacy

• 默认离线运行，--synthetic 模式完全无网络。
• 所有处理在本地完成，不上传用户数据。

License

MIT