Table 3 Methods offered by the application programming interface of the OSHDB framework
From: OSHDB: a framework for spatio-temporal analysis of OpenStreetMap history data
Method | Description |
|---|---|
Data Filters | |
areaOfInterest | Sets the geographical area of interest of the query, i.e. a bounding box or a bounding (multi)polygon. |
timestamps | Sets the temporal limits of the query. Depending on the analysis view, this can either represent a list of independent timestamps (snapshots) or represent a list of time intervals. |
osmType | Filters data by their OSM entity type, i.e. a node, way or relation. |
osmTag | Filters data by their OSM tags. Can either filter for key=* presence of a tag with a given key, key=value presence of a specific tag (key-value combination), key=[values] presence of a tag whose value is in the given list of values, key regex presence of a tag whose value matches the given regular expression, [key=value] presence of at least one tag from the given collection of key-value pairs. |
Aggregation Methods | |
aggregateBy | Defines a custom aggregation method. When applied on a MapReducer, it transforms it into a new MapAggregator with the same settings as the original MapReducer, but which processes the input data in chuncks defined by the indices returned by the given aggregate-by function. When applied on a MapAggregator, the already existing aggregation indices are refined further by the new aggregate-by function (where the resulting index set is defined as the cross product of the existing and the new set of indices). |
aggregateByTimestamp | Aggregates results by a temporal index. This knows about the overall query timestamps parameter and if necessary associates timestamps to the respective time intervals defined for the whole query. |
aggregateByGeometry | Aggregates results by their geometries (spatial position and extent). Accepts a set of arbitrary (multi)polygons which define the aggregation index. If necessary, this method splits and clips the geometries of OSM entities, when they extend over multiple polygons. |
MapReduce Methods | |
map | Performs a data transformation step that calculates one output object for each input object of the processing stream. |
flatMap | Performs a data transformation step that calculates arbitrarily many output objects for each input object of the data stream and flattens the resulting output object in the processing stream. |
filter | Filters the processing stream by the given predicate. |
reduce | Performs a generic reduce operation of the processing stream, which ultimately generates a single result object for the entire processing stream. |
Specialized Reducers | |
sum | Calculates the sum of all values. |
count | Returns the number of entries in the processing stream. |
uniq | Returns the set of unique values in the processing stream. |
countUniq | Returns the number of unique entries in the processing stream. |
average | Calculates the average of all values. |
weightedAverage | Calculates a weighted average over all values. |
estimatedMedian | Returns an estimation of the median of all values in the processing stream, using the T-Digest method [50]. |
estimatedQuanitle(s) | Returns an estimation of the quantile(s) of the distribution of all values in the processing stream, using the T-Digest method [50]. |
collect | Returns a list of all objects in the processing stream. See the stream method below, for a less memory intensive variant of this. |
Other | |
stream | Returns all values as a (JAVA) stream. Equivalent to the collect reducer, but doesn’t need to buffer the whole dataset in memory before returning. |
groupByEntity | Special map function that groups consecutive entries of the processing stream together which belong to the same original OSM entity. |