EO-me goes OpenSearch

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12. January 2018 | Category blog, EO-me, Landsat, Sentinel

EO-me – the Earth Observation Metadata Enhancer platform developed by mundialis enriches the footprints of Sentinel-2 and Landsat-8 scenes with new metadata including scene characterisations like average temperature, precipitation sums, land cover classes and human population of each tile and even dynamic values like the average NDVI at overpass time. Furthermore, EO-me allows users to filter satellite scenes based on their metadata through user defined thresholds.

Until now the EO-me data could be browsed and filtered via the graphical interface of our web application. Now EO-me can also be queried with any OpenSearch client implementation! OpenSearch is a collection of technologies based on XML for describing a search engine so search requests can be formulated in a standardized way as well as a predefined way of sharing search results which are displayed in a standardized and machine-readable format.

This blog post explains how to…

• initialize the search with EO-me
• formulate search requests
• query the search
• and provides some example requests.

 

Initialize Search

If you are using a browser which supports OpenSearch, simply visit https://eome.mundialis.de and a hint will appear in the browser that you can add EO-me as a new search engine. This hint might appear as a plus sign near the search icon in your status bar. Follow this hint to add EO-me as your new satellite data search engine. If your browser does not support the integration or you would like to use the OpenSearch API programmatically, you can reach the OpenSearch API at https://eome.mundialis.de/eome/opensearch.action?q=. How to formulate search requests is explained below. According to the OpenSearch specification, the OpenSearch description document can be used to describe the web interface of a search engine. It is found at https://eome.mundialis.de/eome/opensearch.xml. The document helps to formulate search requests. Within it you can find the tag “Url” with the template attribute. It describes the query string of the search request with the following parameters:

• q – required. Can be empty to return all results or a valid ECQL-Filter to filter results
• startIndex – default value: 0
• count – default value: 25

 

Formulate search requests

To query EO-me OpenSearch, the ECQL (Extended Common Query Language) format is used. ECQL provides a more compact and readable syntax compared to OGC XML filters. For more details look at the ECQL documentation. It explains how to formulate various predicates e.g. to compare expressions. An expression can be an attribute, literal, or computed value. If attributes are compared with literals, have a look at our Data Documentation or the more compact CSV file where we list all available attributes with their data types. The data type needs to be known when formulating requests, e.g. the literal compared with an attribute of the data type string must be delimited by single quotes. It is also possible to formulate spatial predicates with the attribute “wkb_geometry” or temporal predicates with the attribute “sensing_time”.

 

Searching

If you are using a browser which supports OpenSearch, type your ECQL-Filter directly into the search bar and select the EO-me search.
If your browser does not support the integration or you would like to use the OpenSearch API programmatically, follow the Url template from the description document. Replace the values in curly brackets with your request values, e.g. enter your ECQL-Filter behind the parameter “q=”.

 

Example requests

Here are some example requests:

Comments	Browser search field	URL
simple comparison filter	satellite=’sentinel2′	https://eome.mundialis.de/eome/opensearch.action?q=satellite%3D%27sentinel2%27
set start index and number of results returned	–	https://eome.mundialis.de/eome/opensearch.action?q=satellite%3D%27sentinel2%27&startIndex=0&count=10
set output format to application/json	–	https://eome.mundialis.de/eome/opensearch.action?q=satellite%3D%27sentinel2%27&format=application/json
filter with time attribute	sensing_time=2016-12-06T02:01:12Z	https://eome.mundialis.de/eome/opensearch.action?q=sensing_time%3D2016-12-06T02:01:12Z
filter between time attributes	sensing_time BETWEEN 2017-12-13 AND 2017-12-14	https://eome.mundialis.de/eome/opensearch.action?q=sensing_time%20BETWEEN%202017-12-13%20AND%202017-12-14
chain filter with AND	resolution=100 AND soil_podzols>=841 AND satellite=’landsat8′	https://eome.mundialis.de/eome/opensearch.action? q=resolution%3D100%20AND%20soil_podzols%3E%3D841%20AND%20satellite%3D%27landsat8%27
filter with geometry functions	INTERSECTS(wkb_geometry, POINT (5488045 9675519))	https://eome.mundialis.de/eome/opensearch.action?q=INTERSECTS(wkb_geometry,%20POINT%20(5488045%209675519))
filter with bounding box	BBOX(wkb_geometry, 16.005, 48.0408, 16.7686, 48.4585, ‘EPSG:4326’)	https://eome.mundialis.de/eome/opensearch.action?q=BBOX(wkb_geometry,16.005,48.0408,16.7686,48.4585,%27EPSG:4326%27)

 

The example request https://eome.mundialis.de/eome/opensearch.action?q=satellite%3D%27landsat8%27&count=1 will return a response that looks like this:

 

Depending on your browser, the response is recognized as an atom feed. In this case an atom feed response (with parameter count=20) will look like this:

We hope you enjoy the new EO-me OpenSearch interface!