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lib/main/google/olc/README.md

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+Open Location Code
+==================
+
+[![Build Status](https://api.travis-ci.org/google/open-location-code.svg?branch=master)](https://travis-ci.org/google/open-location-code)
+[![CDNJS](https://img.shields.io/cdnjs/v/openlocationcode.svg)](https://cdnjs.com/libraries/openlocationcode)
+
+Open Location Code is a technology that gives a way of encoding location into a form that is
+easier to use than latitude and longitude. The codes generated are called plus codes, as their
+distinguishing attribute is that they include a "+" character.
+
+The technology is designed to produce codes that can be used as a replacement for street addresses, especially
+in places where buildings aren't numbered or streets aren't named.
+
+Plus codes represent an area, not a point. As digits are added
+to a code, the area shrinks, so a long code is more precise than a short
+code.
+
+Codes that are similar are located closer together than codes that are
+different.
+
+A location can be converted into a code, and a code can be converted back
+to a location completely offline.
+
+There are no data tables to lookup or online services required. The
+algorithm is publicly available and can be used without restriction.
+
+Links
+-----
+ * [Demonstration site](http://plus.codes/)
+ * [Mailing list](https://groups.google.com/forum/#!forum/open-location-code)
+ * [Comparison of existing location encoding systems](https://github.com/google/open-location-code/wiki/Evaluation-of-Location-Encoding-Systems)
+ * [Open Location Code definition](https://github.com/google/open-location-code/blob/master/docs/olc_definition.adoc)
+
+Description
+-----------
+
+Codes are made up of a sequence of digits chosen from a set of 20. The
+digits in the code alternate between latitude and longitude. The first
+four digits describe a one degree latitude by one degree longitude
+area, aligned on degrees. Adding two further digits to the code,
+reduces the area to 1/20th of a degree by 1/20th of a degree within the
+previous area. And so on - each pair of digits reduces the area to
+1/400th of the previous area.
+
+As an example, the Parliament Buildings in Nairobi, Kenya are located at
+6GCRPR6C+24. 6GCR is the area from 2S 36E to 1S 37E. PR6C+24 is a 14 meter
+wide by 14 meter high area within 6GCR.
+
+A "+" character is used after eight digits, to break the code up into two parts
+and to distinguish codes from postal codes.
+
+There will be locations where a 10 digit code is not sufficiently precise, but
+refining it by a factor of 20 is i) unnecessarily precise and ii) requires extending
+the code by two digits. Instead, after 10 digits, the area is divided
+into a 4x5 grid and a single digit used to identify the grid square. A single
+grid refinement step reduces the area to approximately 3.5x2.8 meters.
+
+Codes can be shortened relative to a location. This reduces the number of digits
+that must be remembered, by using a location to identify an approximate area,
+and then generating the nearest matching code. Shortening a code, if possible,
+will drop four or more digits from the start of the code. The degree to which a
+code can be shortened depends on the proximity of the reference location.
+
+If the reference location is derived from a town or city name, it is dependent
+on the accuracy of the geocoding service. Although one service may place
+"Zurich" close to the Google office, another may move it by a hundred meters or
+more, and this could be enough to prevent the original code being recovered.
+Rather than a large city size feature to generate the reference location, it is
+better to use smaller, neighbourhood features, that will not have as much
+variation in their geocode results.
+
+Guidelines for shortening codes are in the [wiki](https://github.com/google/open-location-code/wiki).
+
+Recovering shortened codes works by providing the short code and a reference
+location. This does not need to be the same as the location used to shorten the
+code, but it does need to be nearby. Shortened codes always include the "+"
+character so it is simple to compute the missing component.
+
+ * 8F+GG is missing six leading characters
+ * 6C8F+GG is missing four leading characters
+
+Example Code
+------------
+
+The subdirectories contain sample implementations and tests for different
+languages. Each implementation provides the following functions:
+
+ * Test a code to see if it is a valid sequence
+ * Test a code to see if it is a valid full code
+   Not all valid sequences are valid full codes
+ * Encode a latitude and longitude to a standard accuracy
+   (14 meter by 14 meter) code
+ * Encode a latitude and longitude to a code of any length
+ * Decode a code to its coordinates: low, high and center
+ * Shorten a full code relative to a location
+ * Extend a short code relative to a location