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Creating A 'Smart' Linear Referencing Tool
 

Creating A 'Smart' Linear Referencing Tool

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Leveraging ESRI geoprocessing tools and ArcObjects classes, a 'smart' linear referencing tool was created to increase the level of accuracy of the data contained in the annual Montgomery County Bus ...

Leveraging ESRI geoprocessing tools and ArcObjects classes, a 'smart' linear referencing tool was created to increase the level of accuracy of the data contained in the annual Montgomery County Bus Stop Book.

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    Creating A 'Smart' Linear Referencing Tool Creating A 'Smart' Linear Referencing Tool Presentation Transcript

    •  
    • Automating the Sequencing for the Montgomery County Bus Stop Listing Written and Presented By: Matt Yeh
    • Overview
      • Montgomery County Transit publishes an annual report of all the bus stops in the County
      • Sorted by the on street of the bus stop in sequential order
      • Issues with the original process:
        • Used arbitrary search radius parameters that matched stops with the incorrect street
        • Separated state and non-state roads and arbitrarily removed duplicate linearly referenced bus stops
        • Based sequencing on direction values that were often erroneous
        • In essence, assumed far too much and outputted poor results
    • Data Sources
      • Bus Stop point feature class
        • Street name concatenated with type, direction
        • From GPS coordinates
      • County street centerlines
        • Street name, street type, route number
      • State street centerlines
        • Street name concatenated with type, direction, route number
    • Data Issues
      • Bus Stop data
        • Rife with street misspellings (name and type)
        • Unreliable direction values
        • Bus stop points do not intersect centerlines
      • County street data
        • Segmented (optimized for address locating)
        • Unique street type nomenclature
        • Does not include road segments outside of the County
      • State street data
        • Mostly designated by state route number
        • Unique street type nomenclature
        • Direction of polyline (to and from points) did not match direction attribute
    • Goals
      • Merge street nomenclatures
      • Digitize and append missing street segments
      • Correct street polyline direction
      • Match the bus stop with the correlating street centerline
      • Intersect bus stop points with street centerlines in preparation for accurate linear referencing
      • Generate a unique sequence number from linear referencing results
    • Interface
      • VBA form within the ArcGIS Desktop environment
      • Input parameters
        • Bus stop layer (user specifies street value)
        • Road layer (user specifies street and direction values)
        • Output file location
        • Options to correct bus stop street spellings and street polyline direction
    • 1. Merge street nomenclatures
      • Checks the on street of each bus stop against a master list of all street names from the street centerlines
      • If a match is not found, then it displays a list of similar street names from the master list
      • The user can either select from the list or type their own value.
      • The on street of the bus stop is updated to the user-generated value.
    • 2. Digitize and append missing street segments
      • State street data was ultimately used since it was not segmented.
      • Ride-On also serves stops outside of Montgomery County.
      • There were segments missing either because they were never digitized or they were lost when clipped.
    • 3. Correct street polyline direction
      • In some instances, the direction of the street geometry did not match the direction value in the attribute table.
      • If the option was enabled, the script would flip the line when necessary.
      • Some line segments had to be merged and the direction fixed if the road was disjointed.
      • Direction is important for accurate m-values during linear referencing.
    • 4. Match the bus stop with the street centerline
      • For each bus stop, the script would match the route number or street name to all streets within a 2000 foot radius.
      • This is to ensure that it does not get matched to another road with the same name.
      • This screenshot serves as a visualization.
    • 5. Intersect bus stop points with centerlines
      • A new temporary feature class was created and populated with points that intersected the centerline at a 90 degree angle to the original bus stop feature.
      • The new feature class kept the unique bus stop ID and street name from the original bus stop feature.
      • The direction was calculated depending on if it was to the left or the right of the centerline and was based on the direction attribute of the street centerline.
    • 6. Generate a unique sequence number
      • The script makes a call to the linear referencing tool from the geoprocessor object.
      • The results are filtered based on the unique road ID and the direction. It is then sorted by measure.
      • Sequence values are updated starting at 10 in increments of 10.
    • Presenting the data
      • The official bus stop listing consists of two elements:
        • The report listing
        • The appendix maps
      • The report listing
      • The listing was generated from a report created in Microsoft Access.
      • The report is filtered alphabetically by the “on street” of the bus stop and sorted by the sequence number.
      • Other information includes the unique bus stop ID, at street, direction, location, amenities, routes serving, and the appendix map grid.
    • 2. The appendix maps
      • The appendix consists of maps and an index map of the bus stop locations using a clean cartographic style.
      • Maps are based on the ADC standards.
      • Utilized DS MapBook Extension
      • All geographic data is in Maryland State Plane, NAD83, US Survey Feet.
    • Summary
      • By automating the data behind the official bus stop listing, countless man-hours were no longer devoted to the QA/QC process.
      • A standardization of street data would have greatly improved the project with a very high degree of accuracy.
      • Further revisions:
        • Still a work in progress and sometimes buggy (i.e., matching street names and generating next best matches)
        • Sequence bus stops in relation to the bus routes (not only street centerlines)
        • Rely solely on County centerlines
        • Adopt another component software interface standards (eg, CORBA)
    • Questions ?
    • Thank You!