Geoskill: 河流形态变化

Extract shorelines, centerlines and channel widths from multi-temporal water body masks. Quantify shoreline migration, channel migration, change hotspots and migration zones. Use when analyzing river channel changes, identifying erosion/deposition areas, or generating river morphology reports.

ruiduobao@ruiduobao

Install

openclaw skills install @ruiduobao/geoskill-river-morphology-change

River Morphology Change

Extracts shorelines, centerlines, and channel widths from multi-temporal water body masks. Quantifies shoreline migration, channel migration, and change hotspots.

Trigger

Use when the user wants to:

Analyze river channel migration from multi-temporal imagery
Identify erosion and deposition areas along river banks
Compute channel width changes over time
Detect change hotspots where migration is most severe
Generate river morphology change reports
Compare shorelines between different time periods

CLI Usage

bash

# Basic analysis with default parameters
python scripts/river_morphology_change.py --output-dir ./rmc-output

# Custom transect spacing and hotspot percentile
python scripts/river_morphology_change.py \
  --transect-spacing 30.0 \
  --hotspot-percentile 85.0 \
  --output-dir ./rmc-output

# With custom water threshold
python scripts/river_morphology_change.py \
  --water-threshold 0.1 \
  --min-channel-width 15.0 \
  --output-dir ./rmc-output

Parameters

Parameter	Default	Description
`--input-masks`	None	Input water mask GeoTIFF files (ordered by time)
`--transect-spacing`	50.0	Distance between transects in map units
`--min-channel-width`	20.0	Minimum channel width for quality flagging
`--shoreline-method`	threshold	Shoreline extraction method: threshold, canny, manual
`--water-threshold`	0.0	Water extraction threshold (NDWI/MNDWI)
`--hotspot-percentile`	90.0	Percentile threshold for hotspot detection
`--output-dir`	./rmc-output	Output directory

Output

File	Description
`shorelines.geojson`	Shoreline features for each time period
`centerlines.geojson`	Centerline features for each time period
`transects.geojson`	Perpendicular transect lines along centerline
`migration_rates.csv`	Migration distances and rates per transect
`change_hotspots.geojson`	Hotspot features where migration exceeds threshold
`request.json`	Analysis request metadata
`dataset-manifest.json`	Dataset inventory and period information
`output-manifest.json`	Output file inventory and statistics
`qa.json`	Quality assurance checks

Quality Codes

Code	Name	Description
1	high	Clean intersection, single shoreline crossing
2	medium	Small migration or minor complexity
3	low	Multiple intersections, complex geometry
4	invalid	No intersection or processing error

Direction Codes

Code	Name	Description
-1	erosion	Shoreline retreats (water expands)
0	stable	No significant change
1	deposition	Shoreline advances (water contracts)

Key Algorithms

Water Body Extraction

Uses NDWI (Normalized Difference Water Index) or MNDWI (Modified NDWI) to extract water bodies from multispectral imagery:

NDWI = (Green - NIR) / (Green + NIR)
MNDWI = (Green - SWIR1) / (Green + SWIR1)

Centerline Extraction

Uses Voronoi-based medial axis extraction:

Sample points along water polygon boundary
Compute Voronoi diagram of boundary points
Extract Voronoi vertices inside polygon as centerline
Fallback to bounding box centerline if scipy unavailable

Transect Generation

Generates perpendicular transects along the centerline at regular intervals. Each transect is perpendicular to the local tangent direction.

Migration Rate Computation

Uses perpendicular intersection method:

For each transect, find intersection with both shorelines
Measure distance between intersection points
Determine direction (erosion/deposition) based on distance from center

Change Hotspot Detection

Identifies transects where migration distance exceeds the specified percentile threshold (default: 90th percentile).

Exit Codes

Code	Meaning
0	Success
2	Argument error
3	Dependency missing
6	Data validation failure
7	Processing failure

Limitations

Water level changes may be misinterpreted as morphological change
Narrow channels near pixel resolution limit have reduced accuracy
Centerline topology handling is complex for braided/anastomosing channels
Results are auxiliary analysis only; engineering decisions require manual review
Same-season imagery recommended to minimize water level effects

References

Pavelsky & Smith 2008, IEEE GRSL (RivWidth algorithm)
Isikdogan et al. 2017, IGARSS (RivMap automatic river width extraction)
Fisher et al. 2013, Nature Geoscience (global river delta assessment)

数据下载

本 skill 可自动从 Microsoft Planetary Computer 下载数据 (无需 API key):

bash

python river_morphology_change.py --bbox 116,39,117,40 --date-range 2024-06-01,2024-06-30 --output-dir <tmp>

--bbox W,S,E,N: WGS-84 边界框 (西, 南, 东, 北)
--date-range START,END: 日期范围 (YYYY-MM-DD,YYYY-MM-DD)
--aoi-file <path.geojson>: 替代 --bbox 的 GeoJSON 多边形
--cache-dir <path>: 缓存目录 (默认 ~/.geoskill_cache)

当用户只给 --bbox + --date-range (没有 --image) 时，skill 自动下载数据。当用户给 --image 时，走原文件路径 (向后兼容)。