Where Are The Call Boxes Along US Hwy 50? | |
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By: Carol Lau American River College Geography 350: Data Acquisition in GIS; Fall 2008 | |
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Abstract The GIS Support Unit within California Highway Patrol has been tasked with the role of creating spatial data for all of its call boxes across the State of California. There is no centralized database that has current and accurate information. The linage and completeness of the data is unknown. To gain some kind of relative accuracy, six call box sites were selected for this GPS exercise. Maps were created with uncorrected GPS coordinates with an image file from ESRI. The result was then placed in an intranet web application to share and receive feedback from patrolling officers across the state. | |
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Introduction Accurate coordinate data for call boxes is an important part of data creation for the CHP's spatial data library. Currently there is no standard applied to documenting the location of call boxes for the California highway. Some have latitude and longitude, some are missing, and some are duplicates. The sources of these call boxes are unclear. What we know for sure is that it has not been updated for over many years. We know even less about the method of the data the that is currently in our database. In order to verify the relative location, I have selected 6 call boxes along Hwy 50 to compare with CHP's data. GPS was the tool that I used to collect the location data. An image file will be use as background. Sacramento Area Council of Governments who manages 1,275 call boxes and 750 miles of California highway were contacted for background and historical information. Metadata were developed in accordance to FGDC standard. | |
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Background As part of CHP's GIS team that is responsible for the creation and management of its spatial data, it is important to verify the accuracy of the data and thoroughly document the data and its source. It is also of significant importance to the dispatching system for locating requested service that is coming through these call boxes. A demonstration of the GPS tool will provide added value to the end result of the data that is being created. | |
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Methods Six call boxes along US Hwy 50 were selected for this study. The call boxes have coordinate values that are currently in our database system that were extracted as an XML file and SQL Server then export into ArcMap as a shape file. The GPS instrument that was used was a Garmin 76S. WASS was turned off because it crashed every 5 minutes or so. I was able to collect data in two different days and on two separate trips. Data was collected during the mid hours of the morning. I was driving my own vehicle at approximately 60 miles per hour. The GPS parameters were set: WAAS Disabled. Location Format: UTM UPS Map Datum: NAD 83 A web application was created with CHP data. Each patrolling officer is equip with a GPS. When the officer captures data with his/her GPS data then can be verify and add to our data base. Where some of California's highways where call boxes are located.  What a call box look like along a road.  Four maps were created using data form CHP's existing data base and an image layer from ESRI on line. 
  Web application for data viewing and querying: 
Table showing the distant between CHP data and GPS data.  | |
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Conclusion GPS is value added tool when it
comes to data collection. The relative accuracy for this test is rather
vague but acceptable in the sense that it would at lease show us whether
there is or not a call box at a given section of the road. It was a
relative easy and inexpensive exercise compare to other means of surveying
methods.
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References http://resources.esri.com/ arcgisserver/adf/dotnet/ visited October, 2008. http://sacog.org/callboxes/overview.cfm visited October, 2008. | |