Transferring Satellite Imagery to Gaia GPS

In November of 2019 Greg Mills and I pulled off an incredible trip. We flew to the Inupiaq village of Selawik, then ice skated 125 miles to Kotzebue. Our route crossed the Arctic Circle three times, and we skated ~95 miles in the first 1.5 days.

This kind of trip just isn’t possible without relying on today’s remote sensing and other high-tech tools. I used all the tools in my toolbox– Google Earth, windy.com, Gaia GPS, and remote sensing resources. You should review my Remote Sensing tutorials before trying to make sense of the transfer process discussed here.

Sentinel Hub Playground and Sentinel Hub EO Browser are powerful resources for exploring near-real time satellite imagery, but the applications don’t support drawing waypoints or routes over the imagery. Fortunately, we can save georeferenced images from EO Browser, and work with them in in Google Earth or QGIS, producing a kml file that can be loaded into Gaia GPS.

Download Imagery

Create a (free) account with Sentinel Hub EO Browser, sign in. Pull up your layer of interest, at a relevant zoom level. What you see on the screen is what you will download. Click on the “Download image” icon from the options on the far right.

“Download image”

The “Basic” tab allows quick download of non-georeferenced images. Click on the “Analytical” tab to work with georeferenced images.

“Analytical” download options

Image format:

  • JPG or PNG: Not georeferenced
  • KMZ/JPG (smaller file) or KMZ/PNG (larger file): For use in Google Earth
  • Tiff: For use in Avenza (?), QGIS or other GIS applications

Choose an appropriate resolution for your needs. I’ve been using the default 3857 coordinate system.

Avenza Maps

Avenza Maps is a Gaia GPS rival that allows you to load custom maps, any georeferenced image, for navigation offline. You can load three maps before having to upgrade to a paid account. Use an online converter to convert your Tiff to a GeoPDF, then load the GeoPDF into Avenza.

Sentinel georeferenced image in Avenza Maps

Google Earth

The easiest option to work with EO Browser files is in Google Earth. Save as KMZ/JPG or KMZ/PNG (the smaller jpg works fine for me) and open in Google Earth (desktop or browser). Once in Google Earth, you can trace polygons or drop waypoints based on the image layer, then export those features to your phone or GPS like any other kml/kmz. Refer to 3D Route-Planning: Google Earth for tutorials on how to use Google Earth.

QGIS

QGIS is open-source GIS software, a free ~equivalent of ESRI’s ArcGIS. Working with QGIS is not as easy as Google Earth. I’m including it here in case you have a georeferenced image that is not compatible with Google Earth.

Save the EO Browser image as a Tiff. I assume the 8-bit option is fine four our needs. Drag the saved file into QGIS, it should load automatically.

You want a basemap to make sense of where the satellite image is located in the world. Load the QuickMapServices plugin to have access to many basemaps.

(Menu bar) Plugins –> Manage and Install Plugins –> QuickMapServices –> Install

Menu bar Web –> QuickMapServices –> select a basemap. I like OSM Standard and ESRI Satellite.

Note… to view the full list of the options, choose “Settings” from the bottom of the list, click the “More services” tab, and select “Get contributed pack.”

If you select multiple basemaps, you will only see the top layer. Arrange layers in the “Layers” panel, lower left quadrant of QGIS.

To add waypoints, lines, or polygons, you need to create a shapefile for each feature type. You can’t create a shapefile with mixed feature types. Click on the “New Shapefile Layer” button from the toolbar (or Layer –> Create Layer –> New Shapefile Layer from the menu bar), then select the appropriate Geometry type. I’m going to draw Polygons in this demo. Click “Ok”.

QGIS edit controls

The new shapefile should appear in the Layers panel. Select it, then press the pencil icon to edit. In edit mode, click on the green polygon icon to draw polygons (if you are drawing points or lines, you will have different green shapes instead of the polygon). Finish each polygon by right-clicking, and assign an integer id (“1”). You can draw as many polygons as you want within the single shapefile.

A polygon shapefile created in QGIS by tracing over Sentinel imagery

Double-click on the layer item to play with styling, though the styling won’t persist to your exported file. To export the shapefile, right-click on the layer in the layer list, select Export –> Save Feature as…

For use in Google Earth and Gaia GPS, export as KML. The KML file can be loaded directly into Google Earth or Gaia GPS.

Sentinel WMS tiles in QGIS

For folks that want to dive deeper… you can load Sentinel’s tiles directly into QGIS.

Open Developer Tools in your browser and reload the Sentinel EO Browser site with your layer of interest already selected. In Developer Tools, select Network and filter the results with the text “wms.” Right-click on any satellite tile (you can see the previewed tile), select Copy –> Copy Link Address. Open the link in a text editor and remove everything after the question mark (including the question mark).

https://services.sentinel-hub.com/ogc/wms/bfbfc449-320a-4a56-b493-61c9d4fc67e8?service=WMS&request=GetMap&layers=IW-DV-VV-DECIBEL-GAMMA0-ORTHORECTIFIED&styles=&format=image%2Fpng&transparent=true&version=1.1.1&showlogo=false&name=Sentinel-1%20AWS%20(S1-AWS-IW-VVVH)&width=512&height=512&pane=activeLayer&maxcc=100&evalscriptoverrides=&time=2019-11-16%2F2019-11-16&srs=EPSG%3A3857

Truncate to:

https://services.sentinel-hub.com/ogc/wms/bfbfc449-320a-4a56-b493-61c9d4fc67e8

In QGIS, right-click on “WMS/WMTS” in the Browser pane (upper left) –> New Connection. Give the connection a name and post your truncated url in the “URL” field. You should see your new connection as an option, navigate down to the specific layer you want to visualize.

Note that this process only gives you access to that day’s imagery. You can’t use this process to browse other dates.

Gaia GPS

Refer to Navigation with Gaia GPS for a tutorial on importing kml files.

Traced polygons in Gaia GPS

Gaia is actively working on functionality that will allow users to upload georeferenced images. This will allow us to view the actually satellite image, not just the traced features. I can’t wait!

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