Getting Started with STAC APIs

Getting Started with STAC APIs

This post was originally published on James’s personal blog. You can read that post here.


STAC is a specification for “enabling online search and discovery of geospatial assets.” Right now, a lot of work has gone into the core specification, with a 1.0.0-rc1 for the core specification released at the beginning of March. Following the core spec’s 1.0.0 release, more work will go into the API spec.

STAC logo

The tooling story on the way to standing up a STAC API is pretty well ironed out. If you want to create a catalog that follows all the rules in the pretty sizable best practices doc, use PySTAC . If you just want a typed STAC datamodel for building applications on top of STAC, use [ stac-pydantic ] or [ stac4s ]. They’re both dogfooded in STAC API implementations, stac-pydantic in arturo-stac-api and stac4s in Franklin .

One area where tools are lacking is clients. Most clients in stacindex.org are either libraries that require you to write code or full on frontend applications. An exception to this is sat-search , which is a CLI tool. To support a more interactive browsing adventure, I wrote stac-repl , which is built on top of a PureScript client I wrote called purescript-stac . I completed both of these as part of 10% time work at Azavea.

The goal of stac-repl is to provide an interactive, ipython-ish experience around browsing STAC APIs. You can run it with node by downloading the bundled js file from the v0.1.1 release or in a container with docker run jisantuc/stac-repl:0.1.1 .

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You should be able to figure out everything you can do by mashing the <TAB> key. For example, when you start up stac-repl , you only get one completion:

stac > <TAB>
stac > set root url

For this example, I’ll point the root to a catalog of AVIRIS data that can be found at https://franklin.nasa-hsi.azavea.com . Tabbing from there, commands get a little more interesting:

stac > set root url https://franklin.nasa-hsi.azavea.com
stac https://franklin.nasa-hsi.azavea.com > <TAB>
set root url      get conformance   set collection    list collections

Now that we know where the catalog root is, we can check its conformance information, list collections, or pick a specific collection. We don’t know any collections yet, so let’s list some (naturally, by typing just an li and a <TAB>):

stac https://franklin.nasa-hsi.azavea.com > list collections
aviris-classic: AVIRIS is an acronym for the Airborne Visible InfraRed Imaging Spectrometer. AVIRIS is a premier instrument in the realm of Earth Remote Sensing. It is a unique optical sensor that delivers calibrated images of the upwelling spectral radiance in 224 contiguous spectral channels (also called bands) with wavelengths from 400 to 2500 nanometers (nm). AVIRIS has been flown on four aircraft platforms: NASA's ER-2 jet, Twin Otter International's turboprop, Scaled Composites' Proteus, and NASA's WB-57. The ER-2 flies at approximately 20 km above sea level, at about 730 km/hr. The Twin Otter aircraft flies at 4km above ground level at 130km/hr. AVIRIS has flown all across the US, plus Canada and Europe. This catalog contains all AVIRIS missions from 2006 - 2019.

aviris-ng: AVIRIS is an acronym for the Airborne Visible InfraRed Imaging Spectrometer. AVIRIS is a premier instrument in the realm of Earth Remote Sensing. It is a unique optical sensor that delivers calibrated images of the upwelling spectral radiance in 224 contiguous spectral channels (also called bands) with wavelengths from 400 to 2500 nanometers (nm). AVIRIS has been flown on four aircraft platforms: NASA's ER-2 jet, Twin Otter International's turboprop, Scaled Composites' Proteus, and NASA's WB-57. The ER-2 flies at approximately 20 km above sea level, at about 730 km/hr. The Twin Otter aircraft flies at 4km above ground level at 130km/hr. AVIRIS has flown all across the US, plus Canada and Europe. This catalog contains all AVIRIS missions from 2006 - 2019.

aviris-l2-cogs: AVIRIS L2 Refl Imagery converted to pixel-interleaved COGs

aviris-l2-chips: A STAC Collection containing COGs created by the nasa-hsi cog-clip activator

When you list collections, stac-repl remembers their ids, so when you want to pick a collection you can also get tab completions. For example, since all of these collection IDs start with aviris , set collection a<TAB><TAB> completes to:

stac https://franklin.nasa-hsi.azavea.com > set collection aviris-
set collection aviris-classic   set collection aviris-l2-chips  set collection aviris-l2-cogs   set collection aviris-ng

I’ll pick aviris-ng .

stac https://franklin.nasa-hsi.azavea.com > set collection aviris-ng
Set context to collection aviris-ng

Now that I’m in a different context, the available commands are different:

stac https://franklin.nasa-hsi.azavea.com > <TAB>
view               unset collection   locate collection  get conformance    list items         next page          locate item

Here, the new commands are view , unset collection , list items , next page , and locate item . Let’s see what items are available:

stac https://franklin.nasa-hsi.azavea.com > list items
...
Id: "aviris_ang20140605t182232"
Extensions: []
Bbox: [-122.73583300000001,38.558091,-122.676149,38.632746999999995]
Assets:
ftp: ftp://avng_dp:P73axIvP@avng.jpl.nasa.gov/y14_data/ang20140605t182232.tar.gz ((VendorMediaType "application/gzip"))
rgb: http://avirisng.jpl.nasa.gov/aviris_locator/y14_RGB/ang20140605t182232_RGB.jpeg (JPEG)
kml_overlay: http://avirisng.jpl.nasa.gov/aviris_locator/y14_KML/ang20140605t182232_overlay_KML.kml ((VendorMediaType "application/vnd.google-earth.kml+xml"))
rgb_small: http://avirisng.jpl.nasa.gov/aviris_locator/y14_RGB/ang20140605t182232_RGB-W200.jpg (JPEG)
flight_log: http://avirisng.jpl.nasa.gov/cgi/flights_14.cgi?step=view_flightlog&flight_id=ang20140605t (HTML)
kml_outline: http://avirisng.jpl.nasa.gov/aviris_locator/y14_KML/ang20140605t182232_outline_KML.kml ((VendorMediaType "application/vnd.google-earth.kml+xml"))

The API returns them 30 at a time, but I’m only showing the last one on the first page to avoid a huge wall of text. Similarly to listing collections, stac-repl remembers item IDs so that we can tab complete them for item-specific commands.

In this case, the only item-specific command is locate item , so tabbing after that, we can eventually get to

stac https://franklin.nasa-hsi.azavea.com > locate item aviris_ang20140605t182232

This gets us a delightful Mapscii map.

mapscii map

This first release of stac-repl covers only the most basic interactions, but I’m looking forward to building out support for more features like search and transactions.