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# StreamPriorityCalculator

Calculates the primary and secondary streams of multiple stream networks. The key to determining the priority is the shortest path algorithm using multiple iterations within a network graph.

This attribute defines, for each source junction of the network, a unique path (the shortest path) to reach the destination junction. All flow lines included in a path (from the sources to the destination) will have a stream priority attribute set to 1 (primary); all others are set to 2 (secondary).

Before using this transformer, you will need to specify the weights on the network lines in the source data by specifying the Forward Weight Attribute and optionally Reverse Weight Attribute if the network graph is non-oriented.

A weight is a property of a network line typically used to represent a cost for traversing across a network line. An example of a line weight is the length of the line. In a shortest path analysis, you would choose this weight if you wanted the resulting path to be of the shortest length. For line features, 2 weights can be used: one along the digitized direction of the line feature (the forward weight) and one against the digitized direction of the line feature (the reverse weight). The digitized direction of a line feature refers to the order of the vertices.

The goal is to flag the loops (cycles) in the network in order to highlight the primary network lines.

## Expected Output

• Network lines with a stream priority attribute set to 1 (primary) or 2 (secondary). If itâ€™s not possible to determine the priority (if there isn't a destination located on network graph) a stream priority attribute is set to -1. The network lines have also a Graph Identifier attribute. All network lines in a same graph will have the same value in this attribute.
• Unused destination (if the destination is not located on an end point of the network graph)

## Usage Examples

This transformer can be used on network linear flow lines. There are two ways to determine the stream priority attribute:

• To calculate the stream priority attribute for the oriented network lines: for these lines, the digitized direction represents a downstream flow direction.
• To calculate the stream priority attribute for the non-oriented network lines: for these lines, the digitized direction is not significant.

### Calculating the Stream Priority for Oriented Network Lines

When the network lines are oriented, the shortest path should not go against the digitized direction. So initially the weight along the digitized direction (the forward weight) is the length, and the weight against the digitized direction (reverse weight) is a bigger value.

Note that the reverse weight is optional, and usually not required.

### Calculating the Stream Priority for Non-Oriented Network Lines

When the network lines are not oriented, the digitized direction of network lines is not significant. So the weight along the digitized direction (forward weight) and the weight against the digitized direction (reverse weight) are the same. In this case, you can use the same attribute corresponding to the length for both weight parameters. In this way, the loops are removed for the primary network lines (stream priority=1) and you can apply other algorithm to modify the digitized direction. This is how you can make network lines primary (stream priority=1) where the digitized direction represents a downstream flow direction.

## Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

## FME Licensing Level

FME Professional edition and above