21. 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 formatBinConversionProcess
- encodes simple features in a minimized 16-byte format- DensityProcess - computes a density heatmap for a CQL query
HashAttributeProcess
/HashAttributeColorProcess
- computes an additional ‘hash’ attribute which is useful for styling.JoinProcess
- merges features from two different schemas using a common attribute fieldKNearestNeighborSearchProcess
- performs a KNN searchPoint2PointProcess
- aggregates a collection of points into a collection of line segmentsProximitySearchProcess
- searches near a set input features- QueryProcess - performs a Geomesa query, useful as input for nested requests
RouteSearchProcess
- matches features traveling along a given routeSamplingProcess
- 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 stylingTubeSelectProcess
- 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.
21.1. 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
- the
geomesa-process-wps_2.11-<version>.jar
deployed in${GEOSERVER_HOME}/WEB-INF/lib
Note
Some processes also require custom output formats, available separately in the GPL licensed GeoMesa GeoServer WFS module
The GeoMesa datastore plugin and GeoMesa process jars are both 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.
21.2. Processors¶
21.2.1. 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. |
21.2.2. 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. More info here Stat Strings. |
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. More info here transformationsAndProjections. |
21.2.2.1. Stat Strings¶
Stat strings are a GeoMesa domain specific language (DSL) that allows the specification of stats for the iterators to collect. The available stat function are listed below:
Note
Items marked with *
are the name of an attribute, either in your sft or as the result of a transformation or projection.
Note
A TimePeriod is defined as one of the following strings: “day”, “week”, “month”, “year”
Syntax | Parameters | Description |
---|---|---|
Count | ||
Count() |
Counts the number of features. | |
MinMax | ||
MinMax(attribute) |
|
Finds the min and max values of the given attribute. |
GroupBy | ||
GroupBy(attribute,stat) |
|
Groups stats by the given attribute and then runs the given stat on each group. Any stat can be provided. |
Descriptive Stats | ||
DescriptiveStats(attribute) |
|
Runs single pass stats on the given attribute calculating stats describing the attribute such as: count; min; max; mean; and population and sample versions of variance, standard deviation, kurtosis, excess kurtosis, covariance, and correlation. |
Enumeration | ||
Enumeration(attribute) |
|
Enumerates the values in the give attribute and the number of occurrences. |
TopK | ||
TopK(attribute) |
|
TopK of the given attribute |
Histogram | ||
Histogram(attribute,numBins,lower,upper) |
|
Provides a histogram of the given attribute, binning the results into a binned array using the numBins as the number of bins and lower and upper as the bounds of the binned array. |
Freqency | ||
Frequency(attribute,dtg,period,precision) |
|
Estimates frequency counts at scale. |
z3Histogram | ||
Z3Histogram(geom,dtg,period,length) |
|
Provides a histogram similar to Histogram but
treats the geometry and date attributes as a single
value. |
z3Frequency | ||
Z3Frequency(geom,dtg,period,precision) |
|
Provides a freqency estimate similar to Frequency
but treats the geometry and date attributes as a
single value. |
Iterator Stack | ||
IteratorStackCount() |
IteratorStackCount keeps track of the number of times Accumulo sets up an iterator stack as a result of a query. |
21.2.3. 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 |
|
filter |
<wps:ComplexData mimeType="text/plain; subtype=cql">
<![CDATA[some-query-text]]
</wps:ComplexData>
|
output |
<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. |
21.2.3.1. 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"
},
.
.
.
]
}
21.2.4. 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 |
|
attribute |
|
filter |
<wps:ComplexData mimeType="text/plain; subtype=cql">
<![CDATA[some-query-text]]
</wps:ComplexData>
|
histogram |
|
sort |
|
sortByCount |
|
output |
<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” |
21.2.4.1. 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"
}
]
}
21.2.5. 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"
}
]
}