PSRI index for S2 added.

Author: avrecko

sentinel-2/psri/README.md

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+# Plant Senescence Reflectance Index (PSRI)
+
+<a href="#" id='togglescript'>Show</a> script or [download](script.js){:target="_blank"} it.
+<div id='script_view' style="display:none">
+{% highlight javascript %}
+      {% include_relative script.js %}
+{% endhighlight %}
+</div>
+
+## Evaluate and visualize
+ - [Sentinel Playground](https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=41.9027835&lng=12.496365500000024&zoom=12&preset=CUSTOM&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2018-08-01%7C2019-02-20&atmFilter=&showDates=false&evalscript=bGV0IG1pblZhbCA9IC0wLjI7CmxldCBtYXhWYWwgPSAwLjQ7CgpsZXQgdml6ID0gbmV3IEhpZ2hsaWdodENvbXByZXNzVmlzdWFsaXplclNpbmdsZShtaW5WYWwsIG1heFZhbCk7CgpmdW5jdGlvbiBldmFsdWF0ZVBpeGVsKHNhbXBsZXMpIHsKICAgIGxldCB2YWwgPSAoc2FtcGxlc1swXS5CMDYgPiAwKSA%2FIChzYW1wbGVzWzBdLkIwNCAtIHNhbXBsZXNbMF0uQjAyKSAvIHNhbXBsZXNbMF0uQjA2IDogSkFWQV9ET1VCTEVfTUFYX1ZBTDsKICAgIHJldHVybiB2aXoucHJvY2Vzcyh2YWwpOwp9CgpmdW5jdGlvbiBzZXR1cChkcykgewogICAgc2V0SW5wdXRDb21wb25lbnRzKFtkcy5CMDIsIGRzLkIwNCwgZHMuQjA2XSk7CiAgICBzZXRPdXRwdXRDb21wb25lbnRDb3VudCgxKTsKfQ%3D%3D){:target="_blank"}
+ - [EO Browser](https://apps.sentinel-hub.com/eo-browser/?lat=41.9000&lng=12.5000&zoom=10&time=2017-10-08&preset=CUSTOM&datasource=Sentinel-2%20L1C&layers=B01,B02,B03&evalscript=bGV0IG1pblZhbCA9IC0wLjI7CmxldCBtYXhWYWwgPSAwLjQ7CgpsZXQgdml6ID0gbmV3IEhpZ2hsaWdodENvbXByZXNzVmlzdWFsaXplclNpbmdsZShtaW5WYWwsIG1heFZhbCk7CgpmdW5jdGlvbiBldmFsdWF0ZVBpeGVsKHNhbXBsZXMpIHsKICAgIGxldCB2YWwgPSAoc2FtcGxlc1swXS5CMDYgPiAwKSA%2FIChzYW1wbGVzWzBdLkIwNCAtIHNhbXBsZXNbMF0uQjAyKSAvIHNhbXBsZXNbMF0uQjA2IDogSkFWQV9ET1VCTEVfTUFYX1ZBTDsKICAgIHJldHVybiB2aXoucHJvY2Vzcyh2YWwpOwp9CgpmdW5jdGlvbiBzZXR1cChkcykgewogICAgc2V0SW5wdXRDb21wb25lbnRzKFtkcy5CMDIsIGRzLkIwNCwgZHMuQjA2XSk7CiAgICBzZXRPdXRwdXRDb21wb25lbnRDb3VudCgxKTsKfQ%3D%3D){:target="_blank"}
+
+## General description
+
+The plant senescence reflectance index, abbreviated PSRI, is defined as   
+$$PSRI = \frac{B04-B02}{B06}.$$   
+
+It is used for studying vegetation; see [1] for details.
+
+## References
+ [1] Index DataBase, [index.de: PSRI](https://www.indexdatabase.de/db/i-single.php?id=69). Accessed on February 20th 2019.

sentinel-2/psri/script.js

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+let minVal = -0.2;
+let maxVal = 0.4;
+
+let viz = new HighlightCompressVisualizerSingle(minVal, maxVal);
+
+function evaluatePixel(samples) {
+    let val = (samples[0].B06 > 0) ? (samples[0].B04 - samples[0].B02) / samples[0].B06 : JAVA_DOUBLE_MAX_VAL;
+    return viz.process(val);
+}
+
+function setup(ds) {
+    setInputComponents([ds.B02, ds.B04, ds.B06]);
+    setOutputComponentCount(1);
+}