- Variety of protocols, including [http](#http) (curl), [websockets](#websockets), [telnet](#telnet), and the [Redis RESP](https://redis.io/topics/protocol).
- Server responses are [RESP](https://redis.io/topics/protocol) or [JSON](https://www.json.org).
Perhaps the easiest way to get the latest Tile38 is to use one of the pre-built release binaries which are available for OSX, Linux, FreeBSD, and Windows. Instructions for using these binaries are on the GitHub [releases page](https://github.com/tidwall/tile38/releases).
Tile38 can be compiled and used on Linux, OSX, Windows, FreeBSD, and probably others since the codebase is 100% Go. We support both 32 bit and 64 bit systems. [Go](https://golang.org/dl/) must be installed on the build machine.
Tile38 can natively export Prometheus metrics by setting the `--metrics-addr` command line flag (disabled by default). This example exposes the HTTP metrics server on port 4321:
```
# start server and enable Prometheus metrics, listen on local interface only
./tile38-server --metrics-addr=127.0.0.1:4321
# access metrics
curl http://127.0.0.1:4321/metrics
```
If you need to access the `/metrics` endpoint from a different host you'll have to set the flag accordingly, e.g. set it to `0.0.0.0:<<port>>` to listen on all interfaces.
Use the [redis_exporter](https://github.com/oliver006/redis_exporter) for more advanced use cases like extracting key values or running a lua script.
Fields are extra data that belongs to an object. A field is always a double precision floating point. There is no limit to the number of fields that an object can have.
To set a field when setting an object:
```
> set fleet truck1 field speed 90 point 33.5123 -112.2693
> set fleet truck1 field speed 90 field age 21 point 33.5123 -112.2693
Tile38 has support to search for objects and points that are within or intersects other objects. All object types can be searched including Polygons, MultiPolygons, GeometryCollections, etc.
NEARBY searches a collection for objects that intersect a specified radius.
<BRCLEAR="ALL">
### Search options
**WHERE** - This option allows for filtering out results based on [field](#fields) values. For example<br>```nearby fleet where speed 70 +inf point 33.462 -112.268 6000``` will return only the objects in the 'fleet' collection that are within the 6 km radius **and** have a field named `speed` that is greater than `70`. <br><br>Multiple WHEREs are concatenated as **and** clauses. ```WHERE speed 70 +inf WHERE age -inf 24``` would be interpreted as *speed is over 70 <b>and</b> age is less than 24.*<br><br>The default value for a field is always `0`. Thus if you do a WHERE on the field `speed` and an object does not have that field set, the server will pretend that the object does and that the value is Zero.
**MATCH** - MATCH is similar to WHERE except that it works on the object id instead of fields.<br>```nearby fleet match truck* point 33.462 -112.268 6000``` will return only the objects in the 'fleet' collection that are within the 6 km radius **and** have an object id that starts with `truck`. There can be multiple MATCH options in a single search. The MATCH value is a simple [glob pattern](https://en.wikipedia.org/wiki/Glob_(programming)).
**CURSOR** - CURSOR is used to iterate though many objects from the search results. An iteration begins when the CURSOR is set to Zero or not included with the request, and completes when the cursor returned by the server is Zero.
**NOFIELDS** - NOFIELDS tells the server that you do not want field values returned with the search results.
**LIMIT** - LIMIT can be used to limit the number of objects returned for a single search request.
A <ahref="https://en.wikipedia.org/wiki/Geo-fence">geofence</a> is a virtual boundary that can detect when an object enters or exits the area. This boundary can be a radius, bounding box, or a polygon. Tile38 can turn any standard search into a geofence monitor by adding the FENCE keyword to the search.
This command opens a geofence that monitors the 'fleet' collection. The server will respond with:
```
{"ok":true,"live":true}
```
And the connection will be kept open. If any object enters or exits the 6 km radius around `33.462,-112.268` the server will respond in realtime with a message such as:
The most basic object type is a point that is composed of a latitude and a longitude. There is an optional `z` member that may be used for auxiliary data such as elevation or a timestamp.
A [geohash](https://en.wikipedia.org/wiki/Geohash) is a string representation of a point. With the length of the string indicating the precision of the point.
[GeoJSON](https://tools.ietf.org/html/rfc7946) is an industry standard format for representing a variety of object types including a point, multipoint, linestring, multilinestring, polygon, multipolygon, geometrycollection, feature, and featurecollection.
A QuadKey used the same coordinate system as an XYZ tile except that the string representation is a string characters composed of 0, 1, 2, or 3. For a detailed explanation checkout [The Bing Maps Tile System](https://msdn.microsoft.com/en-us/library/bb259689.aspx).
It's recommended to use a [client library](#tile38-client-libraries) or the [Tile38 CLI](#running), but there are times when only HTTP is available or when you need to test from a remote terminal. In those cases we provide an HTTP and telnet options.
Websockets can be used when you need to Geofence and keep the connection alive. It works just like the HTTP example above, with the exception that the connection stays alive and the data is sent from the server as text websocket messages.
The server will respond in [JSON](https://json.org) or [RESP](https://redis.io/topics/protocol) depending on which protocol is used when initiating the first command.
