Dear community,
regarding one of our projects we utilized your open-source
*PointStacker* and adjusted the source code to our needs.
First of all, thanks a lot for providing this highly helpful code as
open-source code! If you are interested, we would
like to contribute to the development of the code with our extensions.We
added input parameters, and
output attributes that might be requested for other use cases as well.
If you are interested in these code extensions, I
would be happy to create a Merge Request. I am refering to
/org/geotools/process/vector/PointStackerProcess.java
<https://github.com/geotools/geotools/blob/master/modules/unsupported/process-feature/src/main/java/org/geotools/process/vector/PointStackerProcess.java>.
Here you can see our customized PointStackerProcess as forked repository
<https://github.com/SaCodematix/geotools/blob/master/modules/unsupported/process-feature/src/main/java/org/geotools/process/vector/PointStackerProcess.java>
as well as the additional unit tests
<https://github.com/SaCodematix/geotools/blob/master/modules/unsupported/process-feature/src/test/java/org/geotools/process/vector/PointStackerProcessTest.java>
(see "CM_POINSTACKER" comments).
In the following you can find more detailed information about our code
extensions:
(Definition: The data set consists of features that are stacked to
cluster. A cluster point then is representing the assigned features. A
StackedPoint contains a feature that is stacked to a cluster. Original
attributes are column names of the data set connected through the
GeoServer datastore. Single points are features that are not assigned to
a cluster with other features, thus, count equals 1.)
In addition to the original source code and the clustering by grid,
our adjustments allow GeoServer users to cluster by an original
attribute, such as state or district (depending on the given data set).
The already existing location options 'nearest' and 'weighted' of how to
position the cluster point are expanded by 'average' (average of all
coordinates of the clustered features) and 'extent' (center of the
minimum and maximumcoordinates in x and y direction). For this, an
additional input parameter _clusterBasis_ is added. Depending on the
data and use case, these locating approaches result in more suitable
cluster point locations on the final map visualization.
The output is expanded by additional returning values. The fids
(*listStackedPointsIDs*) and coordinates (*listStackedPtsCoos*) of the
features belonging to the cluster are listed, as well as all available
properties (attributes & values) for single points
(*singlePointOrigAttributes*) which might be required as FeatureInfo on
the final map.
If the user wants to sort the resulting data collection
(*sortedByField *by overwriting default values of result.SortBy()) by a
specified original attributefield, for instance grades from 1 to 6,
three additional parameters are introduced: _sortField_ (e.g. 'grade'),
_sortBy_ (can be either 'DESCENDING' or 'ASCENDING' (default)), and
_sortValueStackedPt_ to set a representative value for cluster points
that otherwise would contain a list of grades, instead of a single
number that can be sorted. We required this sorting method to influence
the rendered z-order of several PointSymbolizers in the style .sld file,
since the available VendorOption SortBy
<https://docs.geoserver.org/latest/en/user/styling/sld/extensions/z-order/syntax.html>
option had no influence on the z-order of the PointSymbolizers in our
single FeatureTypeStyle since a transformation (PointStacker) is included.
With these extensions, the user also has the possibility to add
original attributes to the output result (_originalAttributes)_. For
instance, ifthe following list is given in the style as list of original
attributes,
<ogc:Function name="parameter">
<ogc:Literal>originalAttributes</ogc:Literal>
<ogc:Literal>*attrA,attrB*,*attrC*</ogc:Literal>
</ogc:Function>
the *extended output* is a FeatureCollection containing the following
attributes:
* fid - the fid of the point representing the cluster
* count - the total number of points in the cluster
* countunique - the number of unique point locations in the cluster
* envBBOX - bounding box coordinates
* *listStackedPointsIDs* - list of all IDs of the stacked features in
the cluster
* *listStackedPtsCoos* - list of all coordinates of the stacked
features in the cluster
* *singlePointOrigAttributes* - only for single points, all of its
data properties (attributes & values)
* *sortedByField* contains the original attribute values of the
sortField, or the representative sortValueStackedPt for cluster
points, or nothing, if no sortField is indicated
* *attrA* - list of values for the first attribute of the input
parameter originalAttributes
* *attrB* - list of values for the second attribute of the input
parameter originalAttributes
* *attrC* - list of values for the third attribute of the input
parameter originalAttributes, and so on.
To approach this output, the following input parameters are added:
@DescribeParameter(
name = "_clusterBasis_",
description = "Indicate basis for clustering methods: 'grid'
(default), or an original " +
"attribute such as state or district (data-dependent).",
defaultValue = "grid"
)
@DescribeParameter(
name = "_originalAttributes_",
description = "List of original attributes that are requested
to be returned. If these " +
"indicated attributes are no actual original
attributes of data, they will be ignored. " +
"Required as comma-separated list of format, e.g:
a,b,c. All in lower case!",
min = 0
)
String argOrigAttributes,
@DescribeParameter(
name = "_sortField_",
description = "Attribute field by which resulting collection
(optionally) can be sorted.",
min = 0
)
String argSortField,
@DescribeParameter(
name = "_sortBy_",
description = "If collection is desired to be sorted through
a specified 'sortField', one can " +
"indicate the method to sort, either 'DESCENDING' or
'ASCENDING' (default) .",
min = 0
)
String argSortOrder,
@DescribeParameter(
name = "_sortValueStackedPt_",
description = "If a collection is desired to be sorted vy a
specified column 'sortField', here" +
"you can indicate the value that will be used for
clustered points as sort value since only" +
"single points will keep the original value of the
'sortField' while clustered points " +
"gather the values of the 'sortField's to an array
which will be replaced by this value " +
"instead, such as 0 (default).",
min = 0
)
String argSortValueStackedPt __
Please let me know, if you have any questions or unclarity. I am looking
forward to any responses, discussions and more information about a
possible Merge Request.
--
All the best
Sabrina Arnold
logo
Felsbachstr. 5/7
D-07745 Jena
Tel: +49 (3641) 30 38-12
Fax: +49 (3641) 30 38-20
Internet: www.codematix.de <https://www.codematix.de/>
e-mail: sarn...@codematix.de
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