# Greyhound

## Exercise

This exercise uses PDAL to fetch data from a Greyhound server. Greyhound is a web server for point cloud data. You can learn more about what it is by visiting http://lidarnews.com/articles/open-source-point-cloud-web-services-with-greyhound/

See the Dublin data used in this example in your browser at

http://potree.entwine.io/data/dublin.html

1. View the `greyhound.json` file in your editor

   >     {
   >         "pipeline": [
   >             {
   >                 "type": "readers.greyhound",
   >                 "url":"data.greyhound.io",
   >                 "depth_begin":0,
   >                 "depth_end":11,
   >                 "resource":"dublin",
   >                 "filter":{
   >                     "Classification": 2
   >                 }
   >             },
   >             {
   >                 "type": "writers.las",
   >                 "compression": "true",
   >                 "minor_version": "2",
   >                 "dataformat_id": "0",
   >                 "filename":"just-ground.laz"
   >             }
   >         ]
   >     }

   > Note

   > If you use the Developer Console when visiting http://speck.ly or http://potree.entwine.io, you can see the browser making requests against the Greyhound server at http://data.greyhound.io

2. Issue the following command in your OSGeo4W Shell.

   >     pdal pipeline greyhound.json

3. Verify that the data look ok:

   >     pdal info just-ground.las | ^
   >         jq .stats.bbox.native

4. Visualize the data in http://plas.io

## Notes

1. readers.greyhound contains more detailed documentation about how to use PDAL’s Greyhound reader .
2. As `depth_end` gets larger, the number of possible points goes up by nearly a factor of 4. Use the `bounds` option of the reader to split up the boxes you are querying to decrease the potential number of points a query might return.