DEM Terrain Analysis

Generate common terrain derivatives from DEM (Digital Elevation Model) data using pure Python.

Features

• Slope — rate of elevation change (degrees or percent)
• Aspect — compass direction of slope (degrees from north)
• Hillshade — simulated illumination visualization
• Contour — iso-line vectors at specified intervals (GeoJSON)
• Curvature — plan and profile curvature
• Terrain Ruggedness Index (TRI) — elevation difference with neighbors
• Topographic Position Index (TPI) — relative neighborhood elevation
• Roughness — max elevation difference in neighborhood
• Flow Direction (D8) — steepest descent direction
• Flow Accumulation — upstream contributing cells
• Watershed — upstream catchment from outlet point
• Viewshed — visible area from observer point

Usage

# Slope analysis
python dem-terrain-analysis.py slope input_dem.tif --output slope.tif --unit degrees

# Aspect analysis
python dem-terrain-analysis.py aspect input_dem.tif --output aspect.tif

# Hillshade
python dem-terrain-analysis.py hillshade input_dem.tif --output hillshade.tif --azimuth 315 --altitude 45

# Contour
python dem-terrain-analysis.py contour input_dem.tif --output contour.geojson --interval 10

# Curvature
python dem-terrain-analysis.py curvature input_dem.tif --output curvature.tif --type plan

# TRI / TPI / Roughness
python dem-terrain-analysis.py tri input_dem.tif --output tri.tif
python dem-terrain-analysis.py tpi input_dem.tif --output tpi.tif --window 3
python dem-terrain-analysis.py roughness input_dem.tif --output roughness.tif

# Hydrology analysis
python dem-terrain-analysis.py flowdir input_dem.tif --output flowdir.tif
python dem-terrain-analysis.py flowacc input_dem.tif --output flowacc.tif

# Batch generate all products
python dem-terrain-analysis.py batch input_dem.tif --output-dir ./terrain/

Algorithm Notes

• 3x3 window convolution: slope, aspect, hillshade, curvature use Zevenbergen-Thorne algorithm
• D8 flow direction: computes slope in 8 directions, picks steepest
• Marching Squares: contour generation via marching squares algorithm
• Pure Python: no external dependencies

---

中文说明

从DEM（数字高程模型）数据派生常见地形产品的纯Python CLI工具。

功能特性

• 坡度 (Slope) - 高程变化率，支持度数和百分比
• 坡向 (Aspect) - 坡面朝向（北向起算角度）
• 山体阴影 (Hillshade) - 模拟光照的可视化产品
• 等高线 (Contour) - 指定间距的等值线（GeoJSON矢量）
• 曲率 (Curvature) - 平面曲率和剖面曲率
• 地形粗糙度指数 (TRI) - 相邻像元高程差
• 地形位置指数 (TPI) - 相对邻域高程
• 粗糙度 (Roughness) - 邻域最大高程差
• 流向 (Flow Direction) - D8算法最陡下降方向
• 汇流累积 (Flow Accumulation) - 上游汇流像元数
• 流域划分 (Watershed) - 给定出口点划定上游流域
• 视域 (Viewshed) - 给定观察点的可视区域

使用方法

# 坡度分析
python dem-terrain-analysis.py slope input_dem.tif --output slope.tif --unit degrees

# 坡向分析
python dem-terrain-analysis.py aspect input_dem.tif --output aspect.tif

# 山体阴影
python dem-terrain-analysis.py hillshade input_dem.tif --output hillshade.tif --azimuth 315 --altitude 45

# 等高线
python dem-terrain-analysis.py contour input_dem.tif --output contour.geojson --interval 10

# 曲率
python dem-terrain-analysis.py curvature input_dem.tif --output curvature.tif --type plan

# TRI/TPI/粗糙度
python dem-terrain-analysis.py tri input_dem.tif --output tri.tif
python dem-terrain-analysis.py tpi input_dem.tif --output tpi.tif --window 3
python dem-terrain-analysis.py roughness input_dem.tif --output roughness.tif

# 水文分析
python dem-terrain-analysis.py flowdir input_dem.tif --output flowdir.tif
python dem-terrain-analysis.py flowacc input_dem.tif --output flowacc.tif

# 批量生成所有产品
python dem-terrain-analysis.py batch input_dem.tif --output-dir ./terrain/

算法说明

• 3×3窗口卷积: 坡度、坡向、山体阴影、曲率使用3×3窗口的Zevenbergen-Thorne算法
• D8流向: 计算8个方向的坡度，选择最陡方向作为流向
• Marching Squares: 等高线生成使用marching squares算法提取等值线
• 纯Python实现: 仅使用Python标准库，无外部依赖