07: Raster 2 - Reprojection, Clipping, Sampling, Zonal Stats

UW Geospatial Data Analysis
CEE467/CEWA567
David Shean

Overview

This week, we are going to revisit rasters. We will cover common operations and strategies, including reprojection, clipping, sampling, zonal statistics, and creating rasters from unstructured point data.

Reading and Tutorials

Please take some time to review the following material (especially if you have limited GIS experience), and come with questions on topics that are unclear, so we can discuss together. There is some overlap in content, but different presentation of the essential material, so hopefully one or more will work for you:

rioxarray

We will dive into xarray in a few weeks, but we will introduce some raster processing and analysis concepts using rioxarray this week. It will be useful to have a general understanding of these two packages from the high-level “quick overview” docs:

• https://docs.xarray.dev/en/stable/getting-started-guide/why-xarray.html

• https://corteva.github.io/rioxarray/stable/getting_started/getting_started.html

Raster Reprojection

• GDAL: https://gdal.org/programs/gdalwarp.html

• rasterio: https://rasterio.readthedocs.io/en/latest/topics/reproject.html

• rioxarray: https://corteva.github.io/rioxarray/stable/examples/reproject.html (much closer to the geopandas to_crs() method)

  • reproject_match: https://corteva.github.io/rioxarray/stable/examples/reproject_match.html (very useful for comparing two rasters)

Raster clipping/masking

• Using rasterio:

  • https://autogis-site.readthedocs.io/en/2021/notebooks/Raster/clipping-raster.html

  • https://rasterio.readthedocs.io/en/latest/topics/masking-by-shapefile.html

• Using rioxarray:

  • https://corteva.github.io/rioxarray/stable/examples/clip_geom.html

Raster resampling/interpolation

• https://rasterio.readthedocs.io/en/latest/topics/resampling.html#resampling-methods

• https://support.esri.com/en/technical-article/000008915

Sampling a raster over polygon areas: zonal statistics

• https://pythonhosted.org/rasterstats/

• https://autogis-site.readthedocs.io/en/2021/notebooks/Raster/zonal-statistics.html

• https://pysal.org/scipy2019-intermediate-gds/deterministic/gds2-rasters.html#zonal-statistics

Sampling a raster at points

• https://github.com/uw-cryo/raster_sampling

Gridding points to raster

• https://www.earthdatascience.org/courses/use-data-open-source-python/data-stories/what-is-lidar-data/lidar-points-to-pixels-raster/

• We will revisit point interpolation and gridding in Lab08

Useful examples of basic raster processing

• https://www.earthdatascience.org/courses/use-data-open-source-python/intro-raster-data-python/raster-data-processing/

  • Nice examples of raster reprojection, clipping, subtraction and export