Tag Archives: imagery

Little Bobtail Lake Fire: Before/After


You may recall the Little Bobtail Lake fire in the Prince George, BC area that burned over 25,000 ha in 2015 (curious to compare 25,000 ha to your area? Check here).

How does it look now? Did the fire burn and kill the entire area? These are some questions that can be explored quite easily now using archived and processed imagery from Astro Digital. I’ve made an example for the Little Bobtail Lake fire here that compares imagery from before the fire (April 9, 2015) and after the fire (June 28, 2015), and here are the steps I used to do it:

  1. Sign up for a free Astro Digital account here.
  2. Sign in and you’ll find yourself at “Mission Control”.
    1. Start a new “task”.
    2. Edit the task.
    3. Select the images you want to process
    4. Submit the task, choosing web map as the output. I wanted true color (visual), false color (mostly land vs. water differentiation), and NDVI (for vegetation health. Green = healthy vegetation, blue/black = dead/dormant/non-vegetated) images, so I chose all of those options.
    5. Submit the task and wait for the images to be processed.
  3. Once the images are ready, follow the instructions for Using Processed Imagery via Mapbox. You need to use Astro Digital’s public Mapbox key to access the web map imagery. I believe it would be possible to download the raw imagery from Astro Digital and make tiles yourself to upload to your own Mapbox account, but I have not done that here. The tradeoff is that Astro Digital limits the key to 100 map views/web page, so if this map is unavailable, you can rest assured that it has gone viral (yay me), so try back tomorrow.
  4. That’s it! The map is here. Try it out. Toggle the layers on and off – “on” layers at the top of the list cover up those underneath, so you need to turn off the upper layers to see the lower layers. Try flipping back and forth to see the difference in NDVI layers – notice that before the fire, the Little Bobtail Lake area looked just like the surrounding area (it’s dark because the vegetation is still coming online after winter), while after the fire, the results are quite striking. Have fun!

Inspiration: AstroDigital blog, Mapbox examples



PG Open Data & WMS


Yesterday, I provided an example for how to load GeoJSON from the City of Prince George Open Data site to your Google Maps API web map. You can also load imagery through OGC WMS. Here is an example showing how to do so.

Note: I recycled most of the code from GISDoctor.com.