Time Dependent Locations
In the case that FEWS is used as a forecasting system the locations dont need to be time dependent in the majority of the cases. The time span of a forecating system is usually several weeks.
For such a short time span the configuration of the locations can be static and if something changes in one of the forecasting locations this can be changed in the FEWS system without keeping track of the situation was before the change.
However when FEWS is used for a Water Information System (WIS) it is important that FEWS also has knowledge of how the location configuration was in the past. In a WIS the time span is much larger and can be as large as 10 or 20 years.
To make it possible to reproduce the time series generated in the past it is necessary that FEWS still has knowledge about how the location configuration was in the past.
The chapter will describe how it is possible to configure time dependent locations. It is also very important to note that only the functionality which is described in this chapter can be considered time depedent.
Configuration of time dependent locations
What exactly is a time dependent location? A time dependent location has a start- and a endtime. In addition the attributes, but also the related locations of the location can vary in time.
A set of time depedent locations can be configured int the LocationSets.xml file. Below is een example file.
The tags visibilityStartTime and visibilityEndTime relate to a columns in the in the file mapLayers/myLocationFile.dbf. The dbf file defines which locations are in the locationSet example.
The column ID defines the id of the location. The column NAME defines the name. The tag visibilityStarTime refers to the column START.
The tag visibiltyEndTime refers to the column END. The combination of both defines for which period this location is valid.
The tag relation with id relation defines a related location. The value is stored in the column REL. The value should be the location id of the related location.
if, for example, the related location of location A changes over time than this should be configured in the following way. In this example we will assume that location A has a related location B
until 1-1-2014. After this date the related location should be location C. First a row should exists in the dbf file of this locationset with the value A in column ID and the column which defines the relation (REL) should have the id
B of location B. The END column should indicate that this is valid until 1-1-2014. A second row with the same value A for the ID column should exists. The START column should indicate that this row is valid from 1-1-2014.
The column REL should have the value C to indicate that the related location is C.
In the case that the related location of a location can vary over time but that a lot of attribute stay constant it is usefull to define the constant attributes in a seperate attribute file. In the example above an attribute file is configured.
The attributes which dont vary over time can be placed in this file. However the attributeFile support the definition of a starttime and endtime in the same way it can be defined for a locationSet.
The grid display supports the usage of time dependent locations and polygons. The time step displayed in the grid display can be varied by using the time slider at the top of the display. In a FEWS system were the locations are not time
dependent the locations and polygons shown will not change when another time step is selected. However when the locations are time dependent the locations and polygons which are shown in the display will change when another time step is selected.
The polygons of the locations of the time series shown in the display will vary automaticly over time when locations are configured to be time dependent. The map layers can be time dependent. An example configuration is shown below.
Time dependent map layers
The explorer and the grid d