spatial networks impact assessment library¶
snail is a Python package to help with analysis of the potential impacts of climate hazards on infrastructure networks.
Install using pip:
pip install nismod-snail
This should bring all dependencies with it. If any of these cause difficulties, try using a conda environment:
conda env create -n snail_env \
python=3.8 geopandas shapely rasterio python-igraph
conda activate snail_env
pip install nismod-snail
If all worked okay, you should be able to run python and import snail:
$ python
>>> import snail
>>> help(snail)
Help on package snail:
NAME
snail - snail - the spatial networks impact assessment library
Using the snail command¶
Once installed, you can use snail directly from the command line.
Split features on a grid defined by its transform, width and height:
snail split \
--features input.shp \
--transform 1 0 -180 0 -1 90 \
--width 360 \
--height 180 \
--output split.gpkg
Split features on a grid defined by a GeoTIFF, optionally adding the values from each raster band to each split feature as a new attribute:
snail split \
--features lines.geojson \
--raster gridded_data.tif \
--attribute \
--output split_lines_with_raster_values.geojson
Split multiple vector feature files along the grids defined by multiple raster files, attributing all raster values:
snail process -fs features.csv -rs rasters.csv
Where at a minimum, each CSV has a column path with the path to each file.
Transform¶
A note on transform - these six numbers define the transform from i,j cell index (column/row) coordinates in the rectangular grid to x,y geographic coordinates, in the coordinate reference system of the input and output files. They effectively form the first two rows of a 3x3 matrix:
| x | | a b c | | i |
| y | = | d e f | | j |
| 1 | | 0 0 1 | | 1 |
In cases without shear or rotation, a and e define scaling or grid cell size, while c and f define the offset or grid upper-left corner:
| x_scale 0 x_offset |
| 0 y_scale y_offset |
| 0 0 1 |