13. GeoMesa Processes¶

The following analytic processes are available and optimized on GeoMesa data stores, found in the geomesa-process module:

ArrowConversionProcess - encodes simple features in the Apache Arrow format
BinConversionProcess - encodes simple features in a minimized 16-byte format
DensityProcess - computes a density heatmap for a CQL query
DateOffsetProcess - modifies the specified date field in a feature collection by an input time period.
HashAttributeProcess/HashAttributeColorProcess - computes an additional ‘hash’ attribute which is useful for styling.
JoinProcess - merges features from two different schemas using a common attribute field
KNearestNeighborSearchProcess - performs a KNN search
Point2PointProcess - aggregates a collection of points into a collection of line segments
ProximitySearchProcess - searches near a set input features
QueryProcess - performs a Geomesa query, useful as input for nested requests
RouteSearchProcess - matches features traveling along a given route
SamplingProcess - uses statistical sampling to reduces the features returned by a query
StatsProcess - returns various stats for a CQL query
TrackLabelProcess - selects the last feature in a track based on a common attribute, useful for styling
TubeSelectProcess - performs a correlated search across time and space
UniqueProcess - identifies unique values for an attribute

Where possible, the calculations are pushed out to a distributed system for faster performance. Currently this has been implemented in the Accumulo data store and partially in the HBase data store. Other back-ends can still be used, but local processing will be used.

13.1. Installation¶

While they can be used independently, the common use case is to use them with GeoServer. To deploy them in GeoServer requires:

a GeoMesa datastore plugin
the GeoServer WPS extension

Note

Some processes also require custom output formats, available separately in the GPL licensed GeoMesa GeoServer WFS module

The GeoMesa datastore plugin is available in the binary distribution in the gs-plugins directory.

Documentation about the GeoServer WPS Extension (including download instructions) is available here.

To verify the install, start GeoServer, and you should see a line like INFO [geoserver.wps] - Found 15 bindable processes in GeoMesa Process Factory.

In the GeoServer web UI, click ‘Demos’ and then ‘WPS request builder’. From the request builder, under ‘Choose Process’, click on any of the ‘geomesa:’ options to build up example requests and in some cases see results.

13.2. Processors¶

13.2.1. ArrowConversionProcess¶

The ArrowConversionProcess converts an input feature collection to arrow format.

Parameters	Description
features	Input feature collection to encode
includeFids	Include feature IDs in arrow file
proxyFids	Proxy feature IDs to integers instead of strings
formatVersion	Arrow IPC format version
dictionaryFields	Attributes to dictionary encode
useCachedDictionaries	Use cached top-k stats (if available), or run a dynamic stats query to build dictionaries
sortField	Attribute to sort by
sortReverse	Reverse the default sort order
batchSize	Number of features to include in each record batch
doublePass	Build dictionaries first, then query results in a separate scan

13.2.2. BinConversionProcess¶

The BinConversionProcess converts an input feature collection to BIN format.

Parameters	Description
features	Input feature collection to query
track	Track field to use for BIN records
geom	Geometry field to use for BIN records
dtg	Use cached top-k stats (if available), or run a dynamic stats query to build dictionaries
label	Attribute to sort by
axisOrder	Reverse the default sort order

13.2.3. DensityProcess¶

The DensityProcess computes a density map over a set of features stored in GeoMesa. A raster image is returned.

Parameters	Description
data	Input Simple Feature Collection to run the density process over
radiusPixels	Radius of the density kernel in pixels. Controls the “fuzziness” of the density map
weightAttr	Name of the attribute to use for data point weights
outputBBOX	Bounding box and CRS of the output raster
outputWidth	Width of the output raster in pixels
outputHeight	Height of the output raster in pixels

13.2.4. DateOffsetProcess¶

The DateOffsetProcess modifies the specified date field in a feature collection by an input time period.

Parameters	Description
data	Input features
dateField	The date attribute to modify
timeOffset	Time offset (e.g. P1D)

13.2.5. HashAttributeProcess¶

The HashAttributeProcess adds an attribute to each SimpleFeature that hashes the configured attribute modulo the configured param.

Parameters	Description
data	Input Simple Feature Collection to run the hash process over
attribute	The attribute to hash on
modulo	The divisor

13.2.5.1. Hash example (XML)¶

HashAttributeProcess_wps.xml is a geoserver WPS call to the GeoMesa HashAttributeProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@HashAttributeProcess_wps.xml localhost:8080/geoserver/wps

The query should generate results that look like this:

{
    "id" : "d0971735-f8fe-47ed-a7cd-2e12280e8ac1",
    "geometry" : {
        "coordinates" : [
            151.1554,
            18.2014
        ],
        "type" : "Point"
    },
    "type" : "Feature",
    "properties" : {
        "Vitesse" : 614,
        "Heading" : 244,
        "Date" : "2016-05-02T18:00:44.030+0000",
        "hash" : 237,
        "CabId" : 150002,
     }
 }

13.2.6. HashAttributeColorProcess¶

The HashAttributeColorProcess adds an attribute to each SimpleFeature that hashes the configured attribute modulo the configured param and emit a color.

Parameters	Description
data	Input Simple Feature Collection to run the hash process over
attribute	The attribute to hash on
modulo	The divisor

13.2.7. JoinProcess¶

The JoinProcess queries a feature type based on attributes from a second feature type.

Parameters	Description
primary	Primary feature collection being queried
secondary	Secondary feature collection to be joined
joinAttribute	Attribute field to join on
joinFilter	Additional filter to apply to joined features
attributes	Attributes to return. Attribute names should be qualified with the schema name, e.g. foo.bar

13.2.8. KNearestNeighborSearchProcess¶

The KNearestNeighborSearchProcess performs a K-nearest-neighbor search on a feature collection using a second feature collection as input. It returns k neighbors for each point in the input data set. Note that if a feature is the nearest neighbor of multiple points in the input data set, it is returned only once.

Parameter	Description
inputFeatures	Input feature collection. The geometries of the features defines the KNN search
dataFeatures	The data set to query for neighbors
numDesired	`k`, number of nearest neighbors to return
estimatedDistance	Estimate of the distance in meters for the `k`-th nearest neighbor, used for the initial query window
maxSearchDistance	Maximum search distance in meters, used to prevent runaway queries of the entire data set

13.2.8.1. K-Nearest-Neighbor Example (XML)¶

KNNProcess_wps.xml is a geoserver WPS call to the GeoMesa KNearestNeighborSearchProcess. In this example, it is chained with a Query process (see Chaining Processes), in order to avoid returning the query features as data. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@KNNProcess_wps.xml localhost:8080/geoserver/wps

13.2.9. Point2PointProcess¶

The Point2PointProcess aggregates a collection of points into a collection of line segments.

Parameters	Description
data	Input feature collection
groupingField	Field on which to group
sortField	Field on which to sort (must be Date type)
minimumNumberOfPoints	Minimum number of points
breakOnDay	Break connections on day marks
filterSingularPoints	Filter out segments that fall on the same point

13.2.9.1. Point2Point example (XML)¶

Point2PointProcess_wps.xml is a geoserver WPS call to the GeoMesa Point2PointProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@Point2PointProcess_wps.xml localhost:8080/geoserver/wps

The query should generate results that look like this:

{
    "id" : "367152240-4",
    "geometry" : {
        "coordinates" : [
            [
                -13.4041,
                37.8067
            ],
            [
                -13.4041,
                37.8068
            ]
        ],
        "type" : "LineString"
    },
    "type" : "Feature",
    "properties" : {
        "Date_end" : "2018-02-05T14:54:36.598+0000",
        "CabId" : 367152240,
        "Date_start" : "2018-02-05T14:53:58.078+0000"
    }
}

13.2.10. ProximitySearchProcess¶

The ProximitySearchProcess performs a proximity search on a Geomesa feature collection using another feature collection as input.

Parameters	Description
inputFeatures	Input feature collection that defines the proximity search
dataFeatures	The data set to query for matching features
bufferDistance	Buffer size in meters

13.2.10.1. Proximity search example (XML)¶

ProximitySearchProcess_wps.xml is a geoserver WPS call to the GeoMesa ProximitySearchProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@ProximitySearchProcess_wps.xml localhost:8080/geoserver/wps

13.2.11. RouteSearchProcess¶

The RouteSearchProcess finds features around a route that are heading along the route and not just crossing over it.

Parameters	Description
features	Input feature collection to query
routes	Routes to search along. Features must have a geometry of LineString
bufferSize	Buffer size (in meters) to search around the route
headingThreshold	Threshold for comparing headings, in degrees
routeGeomField	Attribute that will be examined for routes to match. Must be a LineString
geomField	Attribute that will be examined for route matching
bidirectional	Consider the direction of the route or just the path of the route
headingField	Attribute that will be examined for heading in the input features. If not provided, input features geometries must be LineStrings

13.2.11.1. Route search example (XML)¶

RouteSearchProcess_wps.xml is a geoserver WPS call to the GeoMesa RouteSearchProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@RouteSearchProcess_wps.xml localhost:8080/geoserver/wps

13.2.12. SamplingProcess¶

The SamplingProcess uses statistical sampling to reduces the features returned by a query.

Parameters	Description
data	Input features.
samplePercent	Percent of features to return, between 0 and 1.
threadBy	Attribute field to link associated features for sampling.

13.2.12.1. Sampling example (XML)¶

SamplingProcess_wps.xml is a geoserver WPS call to the GeoMesa SamplingProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@SamplingProcess_wps.xml localhost:8080/geoserver/wps

13.2.13. StatsProcess¶

The StatsProcess allows the running of statistics on a given feature set.

Parameters	Description
features	The feature set on which to query. Can be a raw text input, reference to a remote URL, a subquery or a vector layer
statString	Stat string indicating which stats to instantiate - see below
encode	Return the values encoded as json. Must be `true` or `false`; empty values will not work
properties	The properties / transforms to apply before gathering stats

13.2.13.1. Stat Strings¶

Stat strings are a GeoMesa domain specific language (DSL) that allows the specification of stats for the iterators to collect. See Statistical Queries for an explanation of the available stats.

13.2.14. TrackLabelProcess¶

The TrackLabelProcess returns a single feature that is the head of a track of related simple features.

Parameters	Description
data	Input features
track	Track attribute to use for grouping features
dtg	Date attribute to use for ordering tracks

13.2.14.1. TrackLabel example (XML)¶

TrackLabelProcess_wps.xml is a geoserver WPS call to the GeoMesa TrackLabelProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@TrackLabelProcess_wps.xml localhost:8080/geoserver/wps

13.2.15. TubeSelectProcess¶

The TubeSelectProcess performs a tube select on a Geomesa feature collection based on another feature collection. To get more informations on TubeSelectProcess and how to use it, you can read this tutorial.

Parameters	Description
tubeFeatures	Input feature collection (must have geometry and datetime)
featureCollection	The data set to query for matching features
filter	The filter to apply to the featureCollection
maxSpeed	Max speed of the object in m/s for nofill & line gapfill methods
maxTime	Time as seconds for nofill & line gapfill methods
bufferSize	Buffer size in meters to use instead of maxSpeed/maxTime calculation
maxBins	Number of bins to use for breaking up query into individual queries
gapFill	Method of filling gap (nofill, line)

13.2.15.1. TubeSelect example (XML)¶

TubeSelectProcess_wps.xml is a geoserver WPS call to the GeoMesa TubeSelectProcess. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@TubeSelectProcess_wps.xml localhost:8080/geoserver/wps

13.2.16. QueryProcess¶

The QueryProcess takes an (E)CQL query/filter for a given feature set as a text object and returns the result as a json object.

Parameters	Description
features	The data source feature collection to query. Reference as `store:layername`. For an XML file enter `<wfs:Query typeName=store:layername />` For interactive WPS request builder select `VECTOR_LAYER` & choose `store:layername`
filter	The filter to apply to the feature collection. For an XML file enter: <wps:ComplexData mimeType="text/plain; subtype=cql"> <![CDATA[some-query-text]] </wps:ComplexData> For interactive WPS request builder select TEXT & choose `"text/plain; subtype=cql"` enter the query text in the text box
output	Specify how the output feature collection will be presented. For an XML file enter: <wps:ResponseForm> <wps:RawDataOutput mimeType="application/json"> <ows:Identifier>result</ows:Identifier> </wps:RawDataOutput> </wps:ResponseForm> For interactive WPS request builder check the Generate box and choose “application/json”
properties	The properties / transforms to apply before gathering stats.

13.2.16.1. Query example (XML)¶

QueryProcess_wps.xml is a geoserver WPS call to the GeoMesa QueryProcess that performs the same query shown in the Accumulo-quickstart. It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@QueryProcess_wps.xml localhost:8080/geoserver/wps

The query should generate results that look like this:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [
          -76.513,
          -37.4941
        ]
      },
      "properties": {
        "Who": "Bierce",
        "What": 931,
        "When": "2014-07-04T22:25:38.000+0000"
      },
      "id": "Observation.931"
    }
  ]
}

13.2.17. UniqueProcess¶

The UniqueProcess class is optimized for GeoMesa to find unique attributes values for a feature collection, which are returned as a json object.

Parameters	Description
features	The data source feature collection to query. Reference as `store:layername`. For an XML file enter `<wfs:Query typeName=store:layername />` For interactive WPS request builder select `VECTOR_LAYER` & choose `store:layername`
attribute	The attribute for which unique values will be extracted. Attributes are expressed as a string. For an XML file enter `<wps:LiteralData>attribute-name</wps:LiteralData>`
filter	The filter to apply to the feature collection. For an XML file enter: <wps:ComplexData mimeType="text/plain; subtype=cql"> <![CDATA[some-query-text]] </wps:ComplexData> For interactive WPS request builder select TEXT & choose `"text/plain; subtype=cql"` enter the query text in the text box.
histogram	Create a histogram of attribute values. Expressed as a boolean (true/false). For an XML file enter `<wps:LiteralData>true/false</wps:LiteralData>`
sort	Sort the results. Expressed as a string; allowed values are ASC or DESC. For an XML file enter `<wps:LiteralData>ASC/DESC</wps:LiteralData>`
sortByCount	Sort by histogram counts instead of attribute values. Expressed as a boolean (true/false). For an XML file enter `<wps:LiteralData>true/false</wps:LiteralData>`
output	Specify how the output feature collection will be presented. For an XML file enter: <wps:ResponseForm> <wps:RawDataOutput mimeType="application/json"> <ows:Identifier>result</ows:Identifier> </wps:RawDataOutput> </wps:ResponseForm> For interactive WPS request builder check the Generate box and choose “application/json”

13.2.17.1. Unique example (XML)¶

UniqueProcess_wps.xml is a geoserver WPS call to the GeoMesa UniqueProcess that reports the unique names in in the ‘Who’ field of the Accumulo quickstart data for a restricted bounding box (-77.5, -37.5, -76.5, -36.5)). It can be run with the following curl call:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@UniqueProcess_wps.xml localhost:8080/geoserver/wps

The query should generate results that look like this:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "value": "Addams",
        "count": 37
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd6"
    },
    {
      "type": "Feature",
      "properties": {
        "value": "Bierce",
        "count": 43
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd5"
    },
    {
      "type": "Feature",
      "properties": {
        "value": "Clemens",
        "count": 48
      },
      "id": "fid--21d4eb0_15b68e0e8ca_-7fd4"
    }
  ]
}

13.2.18. Chaining Processes¶

WPS processes can be chained, using the result of one process as the input for another. For example, a bounding box in a GeoMesa QueryProcess can be used to restrict data sent to StatsProcess. GeoMesa_WPS_chain_example.xml will get all points from the AccumuloQuickStart table that are within a specified bounding box (-77.5, -37.5, -76.5, -36.5), and calculate descriptive statistics on the ‘What’ attribute of the results.

The query should generate results that look like this:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [
          0,
          0
        ]
      },
      "properties": {
        "stats": "{\"count\":128,\"minimum\":[29.0],\"maximum\":[991.0],\"mean\":[508.5781249999999],\"population_variance\":[85116.25952148438],\"population_standard_deviation\":[291.74691004616375],\"population_skewness\":[-0.11170819256679464],\"population_kurtosis\":[1.7823482287566166],\"population_excess_kurtosis\":[-1.2176517712433834],\"sample_variance\":[85786.46628937007],\"sample_standard_deviation\":[292.893267743337],\"sample_skewness\":[-0.11303718280959842],\"sample_kurtosis\":[1.8519712064424219],\"sample_excess_kurtosis\":[-1.1480287935575781],\"population_covariance\":[85116.25952148438],\"population_correlation\":[1.0],\"sample_covariance\":[85786.46628937007],\"sample_correlation\":[1.0]}"
      },
      "id": "stat"
    }
  ]
}