Pithon Vithayasricharoen
Department of Civil Engineering
University of Texas at Austin
CE 394K: GIS in Water Resources
Dr. David R. Maidment
There are more than 17,000 miles of load-restricted highways in Texas. These transportation infrastructure facilities were generally constructed prior to the late 1950s, and were designed for lighter wheel loads and axle configurations than are currently allowed by law. In addition, environmental effects have weakened some of these structures. In an effort to protect these facilities from accelerated deterioration, a provision exists in the state law whereby those transportation infrastructure facilities may be legally posted to restrict excessive loading, which means that trucks with the gross load, axle load, axle configuration, length, and width beyond the current size and weight laws cannot pass such road sections.
Currently, the Construction Division Pavements Section manages a database of load-restricted highways and bridge structures maintained by the Texas Department of Transportation (TxDOT). This database is currently not accessible to anyone outside of the Pavements Section. Moreover, the geographic location information of the restricted zones is not available in such database. It means that the database is only in tabular format, which is somewhat difficult for related people to understand the distribution of the load-restricted zones. As a result, TxDOT is interested to develop a database containing the spatial information of the load-restricted zones on the road system of Texas.
This term project focuses on the development of a procedure for projecting the load-restricted zones on a road map of Texas. It is an initial development of a GIS-integrated database of load-restricted zone on highway system.
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The objectives of this study are shown as follows:
To understand Linear Referencing and Dynamic Segmentation in ArcGIS
To develop a procedure for projecting the load-restricted zones on a road map of Texas
To perform a pilot test on the road system in Travis County in order to verify the effectiveness of the developed procedure
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There were five sets of data used in this project shown as follows:
1.
The polygon shapefile displaying the boundary of the state of Texas
downloaded from the USGS web site.
2.
The polygon shapefile of the counties of Texas. This file is also
available in the USGS web site.
3.
The street network shapefile of Travis County. This file is available in
the Bureau of Transportation Statistics web site (BTS). It contains the
information shown as follows:
Highway Name
Length (km)
4. The load-restricted zone database obtained from the Texas Department of
Transportation (TxDOT). It contains the information as shown below:
County
County Name
District
District Name
CS Number
Highway Name
Length (mile)
Limit Description
The
Beginning Milepoint Reference Marker of load restricted zone
The
Reference Marker Sign of the beginning of load restricted zone
The
Reference Marker Displacement from the beginning Milepoint Reference Marker
of the load restricted zone
The Ending Milepoint Reference Marker of load restricted zone
The
Reference Marker Sign of the end of load restricted zone
The
Reference Marker Displacement from the ending Milepoint Reference Marker of
the load restricted zone
Load Limit
5. The Milepoint Reference Marker database obtained from the Center
for Transportation Research (CTR).
Highway Name
Milepoint Reference Marker
Distance from Origin of the Milepoint Reference Marker
on each road in Texas
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The load-restricted location information of the road network in Texas are
coded and referenced based on the Texas Reference Marker System. This system
uses Reference Marker Group, which consists of the Reference Marker Number,
Reference Marker Sign, and Reference Marker Displacement, to identify the
locations of roadway data. The definitions of each component are given below:
Reference Marker Number – The Reference Marker Number is the official number posted on the highways. It is used together with the other components of the Reference Marker Group to locate the roadway data. An example of the Reference Marker is shown below in the Figure 1.
Figure 1: An Example of the Reference
Marker
Reference
Marker Sign – The
Reference Marker Sign is the symbol indicating the ascending or descending
direction to a data attribute or feature from a posted reference marker. The
+ sign indicates the displacement in ascending reference marker direction,
while the – sign indicates the displacement in descending reference marker
direction.
Reference Marker Displacement – The Reference
Marker Displacement is the distance in miles from a posted reference marker
on the highway to a data attribute or feature. It is also used together with
the other components of the Reference Marker Group to locate data on the
highway.
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Highway, city streets, railroads, and rivers, as well as distribution networks such as telephone lines and water and sewer networks, are all examples of linear features. To model these features effectively, good understanding and ability to appropriately analyze them are needed.
Geographic information systems often represent spatial information with a two-dimensional x,y coordinate system. This is good for representing the locations of boundaries, water bodies, and road networks. However, only x,y coordinate system sometimes is not useful for representing linear features. Instead of using x,y measurements, the better way of representing linear features is to use the x,y,m coordinate system. In this coordinate system, each point along a linear feature has a measure value (m value) in addition to x,y coordinates. For example, route I-10, m = 23 kilometer, uniquely identifies a position in geographic space without having to express it in x,y coordinates or latitude-longitude terms. This is so called linear referencing. The measure values along a road network are useful to find out the distance between any two points on the network.
In this study, dynamic segmentation is the tool that is capable of projecting the load-restricted zone on the road network in Texas. Dynamic segmentation allows multiple sets of attributes to be associated with any portion of a linear feature. These attributes can be stored, displayed, queried, and analyzed without affecting the x,y coordinate data of linear features.
There are two components required to perform dynamic segmentation which are:
Routes - A route represents a linear feature such as a city street, highway, or river. Routes contain measure values, which describe the distance along them. The measure values are used to locate data, which describes parts of the route.
Route Events – route events describe route
locations and associated attributes stored in a thematic table of a linear
feature based on measure values (m values).
There are two requirements for performing dynamic segmentation, which are:
Each route event in an event table must include a unique identifier and its measurement along the route.
Each route must have a unique identifier and a measurement system stored with it.
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Pilot test was done for the Travis County in Texas in order to verify the effectiveness of the procedure developed in this project. Each step of the procedure is described as follows.
Because the objective of this study is to project the load-restricted zones on a road map of Texas based on the concepts of linear referencing and dynamic segmentation, all feature classes are needed to have the same spatial reference. This means that all feature classes should be stored in the same feature dataset within the Geodatabase. The tasks in this step are listed as follows:
Add Data to the Geodatabase by selecting Texas as the feature dataset
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In order to perform dynamic segmentation, each route must have a unique identifier as stated above. The identifier used in this project is the Highway Name because it is the only identifier that can be linked between load-restricted zone database and the street network shapefile. However, the shapefile obtained from BTS divides each highway into many sections as shown in the Figure 2.
Figure 2: An Example of a Highway with Many Sections
Therefore, Features that have the same Highway Name were aggregated into only one feature by following these steps.
Go to the Tools menu
Select the Geoprocessing Wizard
Specify TravisRoad.shp as the output shapefile
Based on these steps, the new shape file, TravisRoad.shp, was created. This shapefile was used as a route in the dynamic segmentation process. This shapefile has a unique identifier which is the Highway Name.
Figure 3: Dissolve Features based on an Attribute Function within the Geoprocessing Wizard
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Feature classes existing in a Geodatabase cannot be modified to store measure values. When feature classes are migrated to a Geodatabase for dynamic segmentation process, they must already have measure values (M values) enabled or the ability to store M values must be set before exporting a shapefile to a Geodatabase. The tasks in this step are described as follows:
Start ArcCatalog.
Right Click on TravisRoad.shp. Choose the Export > Shapefile to Geodatabase from the Context menu.
In the Shapefile to Geodatabase dialog box, select the Geodatabase and feature data set created in the previous step.
Enter TravisRoad as the name of the new feature class.
Figure 4: Shapefile to Geodatabase Dialog Box
Click on the Change Settings button. In the Output Settings dialog box, click on the Geometry tab. Check the box next to Enable M Values on the Output.
Figure 5: Enable M values on the Output Checkbox in the Geometry Tab
Still in the Coverage to Geodatabase dialog box, click on the Spatial Reference tab. Click on the Change button. In the Spatial Reference dialog box, click on the M Domain tab and change the Minimum value to –10000 and Precision to 10000.
Figure 6: M Domain Tab in the Spatial Reference Dialog Box.
Click OK to complete the export process.
Verify the TravisRoad feature class properties if the Geometry Type is set to Line and Contains M Values is set to Yes.
After following these tasks, the TravisRoad feature class will have PolylineM geometry which can be used to stored measure values (M values).
Figure 7: TravisRoad Feature Class having the PolylineM Geometry
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Considering the TravisRoad Feature Class, all the vertices of any single feature are visible if such feature is selected. An example of the sketch vertices of Ranch Road 620 feature along with its measure values (M values) is shown in Figure 8. It should be noted that the M values are Not a Number (NaN) because TravisRoad is a newly created feature class. Therefore, measure values have never been assigned to any feature of this feature class. In order to see these vertices, the following tasks are needed.
From the Editor menu on the toolbar, choose Start Editing.
In the toolbar, set Task to Modify Feature. Select the TravisRoad feature.
Click on Ranch Road 620 feature. The sketch vertices, displayed as green squares, will then be visible.
Right click on the selected feature and choose properties from the context menu.
Figure 8: The sketch vertices of Ranch Road 620 feature along with its measure values (M values) set to NaN.
The Measure Values (M Values) can be assigned to all features of the TravisRoad Feature Class following these steps:
Right click on TravisRoad Feature Class and choose Open Attribute Table from the context menu.
In the attribute table, select the Shape field, right click on it, and choose Calculate Values from the context menu.
Figure 9: Calculate Values function within the Shape Field.
In Field Calculator dialog box, Visual Basic for Application (VBA) script code was generated for assigning the measure values to all features of the TravisRoad Feature Class as shown in the figure below.
Figure 10: Field Calculator Dialog Box
The VBA script code will get the
length of each feature based on the Shape_Length attribute to define the maximum
Measure Values of that feature. Measure Values will be interpolated between 0
and the maximum Measure Values. It should be noted that IMSegmentation is the
important interface which makes use of Dynamic Segmentation in ArcGIS.
SetAndInterpolateMsBetween is the method associated with IMSegmentation. This
method sets the Measure Values at the beginning and the end of the geometry and
interpolates the M values between these values.
Eventually, the NaN values in the M column have been replaced by the Measure Values populated by the VBA script in the Field Calculator Dialog Box.
Figure 11: The sketch vertices of Ranch Road 620 feature along with its measure values (M values).
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Load-restricted zone of the highways in Texas are coded and referenced based on the Texas Reference Marker System known as Milepoint Reference Marker. However, to perform the Dynamic Segmentation, the Measure Values (M Values) along linear features are needed. In order to convert the Milepoint Reference Marker to the Measure Values (M Values), the Distance from Origin attribute of the Milepoint Reference Marker database obtained from CTR is needed. It should be noted that the Load-restricted Zone database and the Milepoint Reference Marker database are in the Microsoft Access format.
Because there are more than 2500 records of load-restricted zone, it would be very hard to manually convert the Milepoint Reference Marker to the Measure Values (M Values). Therefore, source code was generated in the Microsoft Visual Basic, known as object-oriented programming, in order to create the Route Events Table for using in the dynamic segmentation process. This source code will read the Reference Marker Number, Reference Marker Sign, and Reference Marker Displacement of both the beginning and end of load-restricted zones from the load-restricted zone database. The Reference Marker Numbers will then be used to extract the Distance from Origin (miles) of each Reference Marker Number from the Milepoint Reference Marker database. Eventually, Reference Marker Sign, and Reference Marker Displacement will be incorporated with the Distance from Origin obtained from the Milepoint Reference Marker in order to calculate the Measure Values (M values) of the beginning and end of load-restricted zones. It should be noted that the measure values obtained from this application have already been converted into units of meters.
Figure 12: Visual Basic Application for creating the Route Events Table of selected county.
This application is capable of creating the Route Events table for the load-restricted zones of each county. The Route Events Table created by this application will be automatically stored in Microsoft Access file. This access file will then be exported as a dBase file to be used as a Route Events Table in the Dynamic Segmentation process. In this study, the route events table of the load-restricted zones of Travis County was created as shown in Figure 13.
Figure 13: The Route Events Tables for the Load-restricted Zones of Travis Counties
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In this step, events will be transformed into features that can be displayed and analyzed on a map. The Add Route Events Dialog Box is used to transform an event table in ArcMap. Each of the tasks in this step is listed as follows.
Go to the Tools menu
Select Add Route Events from the main menu
Specify the Route Events table created in the previous step as the input table
Select Line Events as the type of events the table contains
Choose Highway as the event key field
Specify From-M Field and To-M Field to be FMP and TMP, respectively
Choose TravisRoad as the layer containing the routes that the events refer to
Choose Highway Name as the route key field that identifies the routes.
Figure 14 shows the Add Route Events Dialog Box and all specified attributes.
Figure 14: Add Route Events Dialog Box
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The following figure shows the Load-restricted Zone of the highways in Travis County.
Figure 15: Load-Restricted Zone of highways in Travis County
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GIS is a powerful tool to manage information from different types of data.
GIS can display the results of a complex analysis in a graphical format.
The concepts of Linear Referencing and Dynamic Segmentation are very useful to model and analyze the linear features using routes and route events.
GIS appears to be a tool that can help the analyst pinpoint locations that require further study.
The GIS capabilities make better and more objective information available to the decision making process.
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The future work should consider the following tasks:
Update the Load-Restricted Zone database
Perform the Dynamic Segmentation for every county in the State of Texas
Develop the GIS-integrated database for Load-Restricted Zone of the highway network in the State of Texas
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Zeiler, Michael, Modeling Our World. (The ESRI Guide To Geodatabase Design), ESRI Press, 1999.
Maidment, David R., Arc Hydro. (GIS for Water Resources), ESRI Press, 2002.
Linear Referencing and Dynamic Segmentation in ArcGIS 8.1, An ESRI White Paper, May 2001.
Dynamic Segmentation in ArcGIS, http://www.esri.com/news/arcuser/0702/files/dynseg1.pdf, 2002.
Cadkin, Jennifer, P. Brennan, Dynamic Segmentation in ArcGIS, 2002.
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Dr. David Maidment, Center for Research in Water Resources, University of Texas
at Austin
Dr. Zhanmin Zhang, Center for Transportation Research, University of Texas at Austin
Venkatesh Merwade, Center for Research in Water Resources, University of Texas at Austin
Uarporn Nopmongcol, Center of Energy and Environmental Resources, University of Texas at Austin
Anju Pillai, Center for Transportation Research, University of Texas at Austin
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