Schooner

I’ve had my eyes on schooner-tk for a while now. I don’t remember how I came across it, but it probably has something to do with @btjakes. Anyways, it looks like a useful library, let’s take a look at what it can do.

As usual, I’m going to assume you’re working on OSX and are comfortable with the command line for this tutorial.

From the README:

Schooner-tk is a collection of utilities for averaging, color correcting,
and removing artifacts from satellite images. It complements the GDAL
utilities and the wonderful landsat util.

Schooner-tk currently consists of 5 utilities:

Installation

Schooner requires OpenCV 3, which Homebrew doesn’t install by default. Make sure you get the correct version by running the following:

brew install opencv --devel --without-opencl
brew info opencv

From there, we can install Schooner with:

git clone git@github.com:jacquestardie/schooner-tk.git
cd schooner-tk/src
make

Acquiring data

We’re going to need some data; Landsat-util is the fastest way to get it. I’ll be working with scenes from Landsat 8 taken over Northern Maine.

pip install landsat-util
landsat download LC80110272014262LGN00 LC80100272014255LGN00

Your data will be downloaded to the ~/landsat directory on your machine.

Stitching scenes together

I created color infrared (543) composites of our two scenes. They’re great, but they’re separate, and that’s not what I want.


Let’s use Schooner to stitch them together:

./schooner-stitch \
  ~/landsat/processed/LC80100272014255LGN00/LC80100272014255LGN00_bands_543.TIF \ 
  ~/landsat/processed/LC80110272014262LGN00/LC80110272014262LGN00_bands_543.TIF \
  ~/Desktop/543-stitched.tif

Boom!

But will it blend?

So we can easily stitch images together that are adjacent to one another, but what if we want to combine a stack of scenes together that all have the same boundaries? Depth, instead of width?

Landsat-util provides a handy -p flag to the download parameter that automatically builds a composite for you. By default, it builds a Natural color (432) composite. We’ll take 3 scenes, and see what they look like averaged together.

landsat download -p LC80100272014255LGN00 
landsat download -p LC80100272014223LGN00 
landsat download -p LC80100272013236LGN00



I’m not sure what’s happening with that last composite, but it’s way too dark and is going to affect our blended image significantly so let’s fix the color contrast first.

./schooner-contrast \
    ~/landsat/processed/LC80100272013236LGN00/LC80100272013236LGN00_bands_432.TIF \
    improve-the-contrast.tif

Now that we have the necessary data, we can use schooner-blend.

./schooner-blend \
    ~/landsat/processed/LC80100272014255LGN00/LC80100272014255LGN00_bands_432.TIF \
    ~/landsat/processed/LC80100272014223LGN00/LC80100272014223LGN00_bands_432.TIF \
    improve-the-contrast.tif \
    blend.tif

Yes.

Honestly, the blended image isn’t particularly useful, but I think you can see how finding the average pixel values could be useful.

As always, if you have questions, get in touch!

@jqtrde 27 May 2015