OpenLR decoder configuration

The decoding process is based on four main steps:

1. Find candidate Lines
2. Rate candidate Lines
3. Finding shortest path
4. Filtering shortest path

Find candidates Lines

During the OpenLR Linear location decoding process, each LRP is associated to a set of nodes included in the circle with radius MaxNodeDistance (→ MaxNodeDistance). To each node is associated a candidate line (belonging to the Optima reference network). This candidate line is given a score in order to define the best network link for each LRP.

Candidate lines are both “candidates at nodes” and “direct lines”.

“Candidates at nodes” are lines where end node or start node is equal to a candidate node for the LRP.

“Direct lines” are all lines that are around the LRP coordinate. The LRP coordinate is projected onto the line and the distance between this projection point and the coordinate should be smaller than MaxNodeDistance.

Rate candidate Lines

The rating of a candidate line is computed with the formula:

r = β_n • n_r + β_l • l_r

Parameter	Description
r	Candidate line rating.
lr	Line rating.
nr	Rating of the node associated to the candidate line.
br	Bearing rating.
βn	Node factor. In the OpenLR-Decoder-Properties.xml file, is represented by NodeFactor (→ NodeFactor).
βl	Line factor. In the OpenLR-Decoder-Properties.xml file, is represented by LineFactor (→ LineFactor).

Node rating

n_r = distdiff = max {0, MaxNodeDist − dist[lrp,node]}

Parameter	Description
MaxNodeDist	Maximum node distance. In the OpenLR-Decoder-Properties.xml file, is represented by MaxNodeDistance.
dist[lrp,node]	Distance between the location reference point and the node.

Line rating

l_r = b_r + fow_r + frc_r

Bearing rating

lrpb = location reference point

bdiff = |lrpb - lb|

if bdiff > 180°

  bdiff = 360° - Bdiff

if bdiff > bmax 

  br= -1

else

  if bdiff ≤ bi[Excellent]

    br = br[Excellent]

  else if bdiff ≤ bi[Good]

    br = br[Good]

  else if bdiff ≤ bi[Average]

    br = br[Average]

  else

    br = br[Poor]

Parameter	Description
lb	Bearing of current line.
bi[category]	Bearing interval of the given category (such as Excellent ). In the OpenLR-Decoder-Properties.xml file, is represented by Bearing_Intervals (→ Bearing_Intervals).
br[category]	Bearing rating of the given category (such as Excellent). In the OpenLR-Decoder-Properties.xml file, is represented by Bearing_Rating (→ Bearing_Rating).
bmax	Maximum bearing difference. In the OpenLR-Decoder-Properties.xml file, is represented by maxBearingDiff (→ maxBearingDiff).

A direct line may have been already selected as a candidate at some node. In this case, if the line’s new score is greater than the previous score, the line’s rating is updated with the highest score.

Form of Way rating

Quote from the OpenLR Javadoc:

“The formula uses the rating values defined in the OpenLR properties. The matching between the line and lrp fow attribute is EXCELLENT if both IDs are equal. Otherwise if one of the attributes is undefined then the match is AVERAGE and if no former rule matches then we have a POOR match of the attributes.”

if fowlrp = UNDEFINED OR fowl = UNDEFINED

  fowr = fowr[AVERAGE]

else if fowlrp = fowl

  fowr = fowr[EXCELLENT]

else if fowlrp = MOTORWAY AND fowl = MULTIPLE_CARRIAGEWAY OR

  fowlrp = MULTIPLE_CARRIAGEWAY AND fowl = MOTORWAY OR

  fowlrp = MULTIPLE_CARRIAGEWAY AND fowl = SINGLE_CARRIAGEWAY OR

  fowlrp = SINGLE_CARRIAGEWAY AND fowl = MULTIPLE_CARRIAGEWAY

  fowr = fowr[GOOD]

else if fowlrp = MULTIPLE_CARRIAGEWAY AND fowl = ROUNDABOUT OR

  fowlrp = SINGLE_CARRIAGEWAY AND fowl = ROUNDABOUT OR

  fowlrp = SINGLE_CARRIAGEWAY AND fowl = TRAFFIC_SQUARE OR

  fowlrp = ROUNDABOUT AND fowl = MULTIPLE_CARRIAGEWAY

  fowlrp = ROUNDABOUT AND fowl = SINGLE_CARRIAGEWAY

  fowlrp = ROUNDABOUT AND fowl = TRAFFIC_SQUARE

  fowlrp = TRAFFIC_SQUARE AND fowl = SINGLE_CARRIAGEWAY

  fowlrp = TRAFFIC_SQUARE AND fowl = ROUNDABOUT

  fowlrp = TRAFFIC_SQUARE AND fowl = ROUNDABOUT

  fowr = fowr[AVERAGE]

else

  fowr = fowr[POOR]

Parameter	Description
fowr[category]	Form of way rating of the given category (such as Excellent). In the OpenLR-Decoder-Properties.xml file, is represented by FOW_Rating (→ FOW_Rating).
fowr	Form of way rating.
fowlrp	Form of way of the location reference point.
fowl	Form of way of the current line.

Functional Road Class rating

frcdiff = | frclrp - frcl |

if frcdiff ≤ frci[Excellent]

  frcr = frcr[Excellent]

else if frcdiff ≤ frci[Good]

  frcr = frcr[Good]

else if frcdiff ≤ frci[Average]

  frcr = frcr[Average]

else

  frcr = frcr [Poor]

Parameter	Description
frcr	Functional road class rating.
frclrp	Functional road class of the location reference point.
frcl	Functional road class of the current line.
frci[category]	Functional road class interval of the given category (such as Excellent). In the OpenLR-Decoder-Properties.xml file, is represented by FRC_Intervals (→ FRC_Intervals).
frcr[category]	Functional road class rating of the given category (such as Excellent). In the OpenLR-Decoder-Properties.xml file, is represented by is FRC_Rating (→ FRC_Rating).

FOW definition in Optima

If the table of the lines to map of the Optima DB has a column named fow(of type character varying) and is not null for a given record, then this value is considered. Else it is defined according to the lines attributes as follows:

If strt.fow is not null

  fow = strt.fow

else

  If strt.rdbt  is not null and strt.rdbt > 0

    fow = ROUNDABOUT

  else strt.ramp  if is not null and strt.ramp > 0

    fow = SLIP_ROAD

  else if strt.cont if is not null and strt.cont > 0

    fow = MOTORWAY

  else if strt.hier <= 2

    fow = MULTIPLE_CARRIAGEWAY

  else if (strt.disa  is null or strt.disa = 0) and (strt.daut is null or strt.daut = 0)

    fow = SINGLE_CARRIAGEWAY

  else

    fow = UNDEFINED

Therefore:

• strt.rdbt>0 if the street is a roundabout.
• strt.ramp>0 if the street is a ramp (sliproad).
• strt.cont>0 if the street has controlled access (that is if the street is a motorway).
• strt.daut>0 if the street is not allowed to cars.

Finding shortest path

When the First LRP, the Last LRP, and eventually Intermediate LRPs are associated to a network link, a shortest path search is performed in order to find the sequence of streets that identifies the OpenLR Linear location (LRP sequence).

The search must start from the street associated to the first LRP and must terminate on the street associated to the last LRP, crossing the streets associated to the intermediate LRPs.

Filtering shortest path

The route filtering is based two threshold parameters: FRC_Variance and DNPVariance.

Parameter	Description
frcl> frclrp+ FRC_Variance	Each line must have a functional road class big enough in order to prevent the assignment of location reference referring to high importance roads to streets of lower importance. The threshold is defined through the FRC_Variance (→ FRC_Variance).
DNP - DNPVariance < length of mapping < DNP + DNPVariance	The total line of the mapping length_lmr should be comparable with the DNP within the error bars given by DNPVariance (→ DNPVariance).

The decoder is based on the library OpenLR 1.4.3.

The library is loaded by Optima and contains a set of parameters with all the necessary default values.

You can define the decoding parameters setting the associated values specified in the configuration file:

/opt/ptv-optima-vv.n.xxxxstandalone/configuration/optima/optima_library_conf/openlr/OpenLR-Decoder-Properties.xml

An example of configuration file:

                    <?xml version="1.0" encoding="UTF-8"?>

<!-- The decoder configuration strongly influences the quality 
of the georeferencing process and it impacts the traffic flow real time data quality. 
Changes to this configuration must be conscious.-->

<OpenLRDecoderProperties 	
						
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:olr="http://www.example.org/OpenLRpropertiesProperties/"
    xsi:noNamespaceSchemaLocation="http://www.example.org/OpenLRpropertiesProperties/OpenLRDecoderProperties.xsd" >
	
    <!-- Factor multiplying the total node rating  -->                         
    <NodeFactor>3</NodeFactor>
    
    <!-- Factor multiplying the total line rating  -->
    <LineFactor>3</LineFactor>
	
    <!-- Maximum allowed distance between candidate node and location reference point -->
    <MaxNodeDistance>200</MaxNodeDistance>  
    
    <!-- Maximum allowed angle between candidate line bearing and location reference point bearing -->
    <maxBearingDiff>45</maxBearingDiff>
    
    <!-- Definition of the bearing intervals -->
    <Bearing_Intervals>
        <Excellent>11</Excellent>
        <Good>22</Good>
        <Average>33</Average>
    </Bearing_Intervals>
    
    <!-- Rating assigned to each category of the bearing intervals -->
    <Bearing_Rating>
        <Excellent>100</Excellent>
        <Good>75</Good>
        <Average>50</Average>
        <Poor>25</Poor>
    </Bearing_Rating>
	
    <!-- Allowed tolerance on low importance (high FRC) candidate lines -->
    <FRC_Variance>3</FRC_Variance> 					
						
    <!-- Definition of the FRC intervals -->
    <FRC_Intervals>
        <Excellent>0</Excellent>
        <Good>1</Good>
        <Average>2</Average>
    </FRC_Intervals>
	
	<!-- Rating assigned to each category of the FRC intervals -->
    <FRC_Rating>
        <Excellent>100</Excellent>
        <Good>75</Good>
        <Average>50</Average>
        <Poor>25</Poor>
    </FRC_Rating>    
    
    <!-- Rating assigned to each category of the FOW intervals -->
    <FOW_Rating>
        <Excellent>80</Excellent>
        <Good>60</Good>
        <Average>40</Average>
	 <Poor>20</Poor>
    </FOW_Rating>	
	
    <!-- Allowed tolerance on the length of the candidate path -->
    <DNPVariance>150</DNPVariance>
	
    <!-- Minimum allowed rating of the candidate line -->
    <MinimumAcceptedRating>800</MinimumAcceptedRating>
	
    <!-- Maximum number of attempts to find a shortest path -->
    <MaxNumberRetries>5</MaxNumberRetries>
	
    <!-- Unchangeable parameters -->
    <BearingDistance>20</BearingDistance>
    <SameLineDegradation>0.10</SameLineDegradation>
    <ConnectedRouteIncrease>0.10</ConnectedRouteIncrease>
		
</OpenLRDecoderProperties>
                

The values specified into the configuration file override the library default values.

The parameters of the decoder can be organized in two different sets:

• Parameters editable.
• Parameters not editable (unchangeable).

Parameters editable

You can edit the listed parameters according with your decoding quality needs.

Parameters not editable (unchangeable)

In the table are listed very specific parameters, with the associated library default value.

Important:  It is really important to avoid any changes on this set of parameters!

The file OpenLR-Decoder-Properties.xml is validated by the XSD schema:

/opt/ptv-optima-vv.n.xxxxstandalone/configuration/optima/optima_library_conf/openlr/OpenLR-Decoder-Properties.xsd

A log message is provided three cases:

1. The decoder configuration is valid (info):

   OPENLR Decoding properties file has valid xml schema

2. The decoder configuration is not valid (error):

   OPENLR Decoding properties file has not been validated

3. The decoder configuration validator file is absent (warn):

   Missing OPENLR Decoding properties validator file