sankee 0.0.4

Visualize classified time series data with interactive Sankey plots in Google Earth Engine.

sankee

Visualize changes in classified time series data with interactive Sankey plots in Google Earth Engine

Contents

• Description
• Installation
  • Using Pip
  • Using Conda
  • For Developers
• Requirements
• Quick Start
  • Using a Premade Dataset
  • Using a Custom Dataset
• Features
  • Modular Datasets
  • Flexible Time Series
  • Integration with geemap
  • Editable Plots
• API
• Contributing

Description

sankee provides a dead-simple API that combines the power of GEE and Plotly to visualize changes in land cover, plant health, burn severity, or any other classified imagery over a time series in a region of interst using interactive Sankey plots. Use a library of built-in datasets like NLCD, MODIS Land Cover, or CGLS for convenience or define your own custom datasets for flexibility.

sankee works by randomly sampling points in a time series of classified imagery to visualize how cover types changed over time.

Installation

Using Pip

pip install sankee

Using Conda

sankee can be downloaded through conda-forge within a Conda environment.

conda create -n sankee
conda activate sankee
conda install -c conda-forge sankee

For Developers

Currently, pipenv is used to track development dependencies. The following steps install and activate a pipenv development environment.

# Create a local repository
git clone https://github.com/aazuspan/sankee
cd sankee

# Install all dependencies, including development tools, and activate the environment
pip install pipenv
pipenv install -d
pipenv shell

# Set the directory so that pre-commit testing will be run
scripts/install-hooks.bash

# Optionally, tests can be run manually
scripts/run-tests.bash

Requirements

• An authenticated GEE Python environment (offical guide)

Quick Start

Using a Premade Dataset

Datasets in sankee are used to apply labels and colors to classified imagery (e.g. a value of 42 in an NLCD 2016 image should be labeled "Evergeen forest" and colored green). sankee includes premade Dataset objects for common classified datasets in GEE like the National Land Cover Dataset (NLCD), MODIS land cover, Copernicus Global Land Service (CGLS), and the Landscape Change Monitoring System (LCMS). See datasets for a detailed explanation.

import ee
import sankee

ee.Initialize()

# Choose a premade dataset object that contains band, label, and palette information for NLCD
dataset = sankee.datasets.NLCD2016

# Select images to compare
nlcd2001 = ee.Image("USGS/NLCD/NLCD2001")
nlcd2016 = ee.Image("USGS/NLCD/NLCD2016")

# Build a list of images
img_list = [nlcd2001, nlcd2016]
# Build a matching list of labels for the images (optional)
label_list = ["2001", "2016"]

# Define an area of interest
vegas = ee.Geometry.Polygon(
    [[[-115.01184401606046, 36.24170785506492],
      [-114.98849806879484, 36.29928186470082],
      [-115.25628981684171, 36.35238941394592],
      [-115.34692702387296, 36.310348922031565],
      [-115.37988600824796, 36.160811202271944],
      [-115.30298171137296, 36.03653336474891],
      [-115.25628981684171, 36.05207884201088],
      [-115.26590285395109, 36.226199908103695],
      [-115.19174513910734, 36.25499793268206]]])

# Choose a title to display over your plot (optional)
title = "Las Vegas Urban Sprawl, 2001 - 2016"

# Generate your Sankey plot
plot = sankee.sankify(img_list, vegas, label_list, dataset, max_classes=4, title=title)
plot

Note on NLCD1992

The 1992 version of NLCD used a different legend and classification technique than later versions. Making comparisons between 1992 and later years is not recommended, but can technically be done by reclassifying 1992 data using the sankee.datasets.convert_NLCD1992_to_2016 function, as shown below. This function uses the crosswalk published in Completion of the National Land Cover Database (NLCD) 1992–2001 Land Cover Change Retrofit Product by Fry et al., 2009 to approximately match 1992 classes to the classes used in later years. However, users should be aware that changes in classification between years may be due to changes in classification method rather than changes actual land cover.

# Reclassify NLCD1992 before attempting to make comparisons with other NLCD years
nlcd1992 = sankee.datasets.convert_NLCD1992_to_2016(ee.Image("USGS/NLCD/NLCD1992"))

Using a Custom Dataset

Datasets can also be manually defined for custom images. In this example, we'll classify 1-year and 5-year post-fire Landsat imagery using NDVI and visualize plant recovery using sankee.

import ee
import sankee

ee.Initialize()

# Load fire perimeters from MTBS data
fires = ee.FeatureCollection("users/aazuspan/fires/mtbs_1984_2018")
# Select the 2014 Happy Camp Complex fire perimeter in California
fire = fires.filterMetadata("Fire_ID", "equals", "CA4179612337420140814")

# Load imagery 1 year after fire and 5 years after fire
immediate = ee.Image("LANDSAT/LC08/C01/T1_TOA/LC08_045031_20150718")
recovery = ee.Image("LANDSAT/LC08/C01/T1_TOA/LC08_046031_20200807")

# Calculate NDVI
immediate_NDVI = immediate.normalizedDifference(["B5", "B4"])
recovery_NDVI = recovery.normalizedDifference(["B5", "B4"])

# Reclassify continuous NDVI values into classes of plant health
immediate_class = ee.Image(1) \
  .where(immediate_NDVI.lt(0.3), 0) \
  .where(immediate_NDVI.gt(0.5), 2) \
  .rename("health")

recovery_class = ee.Image(1) \
  .where(recovery_NDVI.lt(0.3), 0) \
  .where(recovery_NDVI.gt(0.5), 2) \
  .rename("health")

# Specify the band name for the image
band = "health"

# Assign labels to the pixel values defined above
labels = {
    0: "Unhealthy",
    1: "Moderate",
    2: "Healthy"
}
# Assign colors to the pixel values defined above
palette = {
    0: "#e5f5f9",
    1: "#99d8c9",
    2: "#2ca25f"
}

# Define the images to use and create labels to describe them
img_list = [immediate_class, recovery_class]
label_list = ["Immediate", "Recovery"]

# Generate your Sankey plot
plot = sankee.sankify(img_list, fire, label_list, band=band, labels=labels, palette=palette, scale=20)
plot

Features

Modular Datasets

Datasets in sankee define how classified image values are labeled and colored when plotting. label and palette arguments for sankee functions can be manually provided as dictionaries where pixel values are keys and labels and colors are values. Every value in the image must have a corresponding color and label. Datasets also define the band name in the image in which classified values are found.

Any classified image can be visualized by manually defining a band, palette, and label. However, premade datasets are included for convenience in the sankee.datasets module. To access a dataset, use its name, such as sankee.datasets.NLCD2016. To get a list of all dataset names, run sankee.datasets.names(). Datasets can also be accessed using sankee.datasets.get() which returns a list of Dataset objects that can be selecting by indexing.

# List all sankee built-in datasets
sankee.datasets.names()

>> ['LCMS_LU',
    'LCMS_LC',
    'NLCD2016',
    'MODIS_LC_TYPE1',
    'MODIS_LC_TYPE2',
    'MODIS_LC_TYPE3',
    'CGLS_LC100']

# Preview a list of available images belonging to one dataset
sankee.datasets.CGLS_LC100.get_images(3)

>> ['COPERNICUS/Landcover/100m/Proba-V-C3/Global/2015',
    'COPERNICUS/Landcover/100m/Proba-V-C3/Global/2016',
    'COPERNICUS/Landcover/100m/Proba-V-C3/Global/2017',
    '...']

Flexible Time Series

sankee can handle any length of time series. The number of images will determine the number of time steps in the series. The example below shows a three-image time series.

Integration with geemap

geemap is a great tool for exploring changes in GEE imagery before creating plots with sankee. Integration is quick and easy. Just use geemap like you normally would, and pass the images and feature geometries to sankee for plotting. Click here for an interactive notebook that demonstrates using sankee with geemap.

Editable Plots

The plot returned by sankee.sankify is a plotly.graph_objs._figure.Figure which can be easily edited after creation like any other Plotly Graph Object. The plot.update_layout function has many options which can be used to change things like plot size or label styles. For example, we can update plot size and title color of an existing plot using the code below.

plot = sankee.sankify( ... )
plot.update_layout(height=1000, width=2400, title_font_color="red")

API

Core function

sankee.sankify(image_list, region, label_list, dataset, band, labels, palette, exclude, max_classes, n, title, scale, seed, dropna)

Generate n random samples points within a region and extract classified pixel values from each image in an image list. Arrange the sample data into a Sankey plot that can be used to visualize changes in image classifications.

Arguments

• image_list (list)

  • An ordered list of images representing a time series of classified data. Each image will be sampled to generate the Sankey plot. Any length of list is allowed, but lists with more than 3 or 4 images may produce unusable plots.

• region (ee.Geometry)

  • A region to generate samples within.

• label_list (list, default: None)

  • An ordered list of labels corresponding to the images. The list must be the same length as image_list. If none is provided, sequential numeric labels will be automatically assigned starting at 0. Labels are displayed on-hover on the Sankey nodes.

• dataset (sankee.datasets.Dataset, default: None)

  • A premade dataset that defines the band, labels, and palette for all images in image_list. If a custom dataset is being used, provide band, labels, and palette instead.

• band (str, default: None)

  • The name of the band in all images of image_list that contains classified data. If none is provided, dataset must be provided instead.

• labels (dict, default: None)

  • The labels associated with each value of all images in image_list. Every value in the images must be included as a key in the labels dictionary. If none is provided, dataset must be provided instead.

• palette (dict, default: None)

  • The colors associated with each value of all images in image_list. Every value in the images must be included as a key in the palette dictionary. If none is provided, dataset must be provided instead. Colors must be supported by Plotly.

• exclude (list, default: None)

  • An optional list of pixel values to exclude from the plot. Excluded values must be raw pixel values rather than class labels. This can be helpful if the region is dominated by one or more unchanging classes and the goal is to visualize changes in smaller classes.

• max_classes (int, default: None)

  • If a value is provided, small classes will be removed until max_classes remain. Class size is calculated based on total times sampled in the time series.

• n (int, default: 100)

  • The number of samples points to randomly generate for characterizing all images. More samples will provide more representative data but will take longer to process.

• title (str, default: None)

  • An optional title that will be displayed above the Sankey plot.

• scale (int, default: None)

  • The scale in image units to perform sampling at. If none is provided, GEE will attempt to use the image's nominal scale, which may cause errors depending on the image projection.

• seed (int, default: 0)

  • The seed value used to generate repeatable results during random sampling.

• dropna (bool, default: True)

  • If the region extends into areas that contain no data in any image, some samples may have null values. If dropna is True, those samples will be dropped. This may lead to fewer samples being returned than were requested by n.

Returns

• A Plotly Sankey plot object.

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Dataset functions

sankee.datasets.names()

Get a list of supported dataset names. Names can be used to access datasets using sankee.datasets.{dataset_name}.

Arguments

• None

Returns (list)

• A list of strings for supported dataset names.

sankee.datasets.get(i)

Get a list of supported sankee.datasets.Dataset objects.
Arguments

• i (int, default: None)
  • An optional index to retrieve a specific dataset.

Returns (list)

• A list of supported sankee.datasets.Dataset objects. If i is provided, only one object is returned.

Example

# Get the first Dataset object
sankee.datasets.get(0)

>> <sankee.datasets.Dataset> USFS Landscape Change Monitoring System v2020.5

sankee.datasets.convert_NLCD1992_to_2016(img)

Convert the values of an NLCD1992 image to match the legend of other NLCD years using the Fry et al., 2009 crosswalk. This function must be run before attempting to use NLCD1992 with the NLCD2016 dataset because the 1992 legend contains values that are not included in the 2016 dataset. This function should be used with caution because NLCD1992 is not directly comparable with later years due to differences in the classification methodology.

Arguments

• img (ee.Image)
  • The NLCD1992 image to reclassify.

Returns (ee.Image)

• An image with the 1992 NLCD legend reclassified to match the 2016 NLCD legend.

sankee.datasets.Dataset.get_images(max_images)

Get a list of image names in the collection of a specific dataset.
Arguments

• max_images (int, default: 20)
  • The max number of images to return.

Returns (list)

• A list of image names that can be used to load ee.Image objects.

Example

sankee.datasets.NLCD2016.get_images(3)

>> ['USGS/NLCD/NLCD1992', 'USGS/NLCD/NLCD2001', 'USGS/NLCD/NLCD2001_AK', '...']

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Dataset properties and attributes

sankee.datasets.Dataset.collection

• Return the image collection associated with the dataset as an Earth Engine object.

sankee.datasets.Dataset.df

• Return a Pandas dataframe describing the classes, labels, and colors associated with the dataset.

sankee.datasets.Dataset.id

• Return the system ID of the image collection.

Contributing

If you find bugs or have feature requests, please open an issue!

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