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To work with temporal attributes, you need to have some in your stream. There are multiple ways to create temporal attributes. You can use the existing aggreagtion functions which "learn" a function from the previous elements. These create linear or spline functions and prdict, i.e. extrapolate or interpolate unknown points in time.
For example, you can create a temporal double from a stream of double values. "wh" is an attribute with a double value. In this case, there are "wh" measurements from different sources, which can be grouped by their "id". The eval_at_outdating is not necessary. It reduces the number of output elements of the aggregation operator and can be handy in some cases, but problematic in others.
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/// Convert the wh-attribute to a temporal double
temporalize = AGGREGATION({
aggregations = [['function' = 'ToTemporalDouble', 'input_attributes' = 'wh', 'output_attributes' = 'temp_wh']],
group_by = ['id'],
eval_at_outdating = false
},time) |
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) |
Another possibility is to crate a temporal spatial point with a spline or a linear function:
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/// Temporalize the location attribute
temporalize = AGGREGATION({
aggregations = [['function' = 'TOLINEARTEMPORALPOINT', 'input_attributes' = 'SpatialPoint', 'output_attributes' = 'temp_SpatialPoint']],
group_by = ['id'],
eval_at_outdating = false
}, createSpatialObject) |
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}, createSpatialObject) |
Another option is that you already know the future movement or at least some points. An example function which uses this mechanism is the "FromTemporalGeoJson" map function. It creates a temporal function from the given source. This can be an option, if you know the future values, e.g., because your navigation systems provides a route.
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/// A known trajectory
input_traj = ACCESS({
source='Source',
wrapper='GenericPull',
transport='File',
protocol='Text',
datahandler='Tuple',
metaattribute = ['TimeInterval', 'PredictionTimes'],
options=[
['filename', '/home/tobi/dev/odysseus_workspace/phd-workspace/Moving Object/Basic Queries/predefinedTrajectory/temporalGeoJson.txt'],
['Delimiter', ';']
],
schema=[['data', 'String']]
})
json = MAP({
expressions = [['FromTemporalGeoJson(data)','tempTrajectory']]
},input_traj) |
The schema of the temporal GeoJson is copied from the Leaflet library, because there is no common standard for temporal GeoJson: https://github.com/socib/Leaflet.TimeDimension#ltimedimensionlayergeojson
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