Utilize detailed CAD maps you already have
The development and of a Geographic Information Systems (GIS) for water, wastewater or storm drain systems present several unique challenges not typical to most municipal GIS conversion projects. First, the GIS database is typically based on engineering drawings created for use by experienced in house staff. This type map is not suitable for interpretation by GIS digitizing technicians.
The second issue involves the application of data after the conversion process. GIS data created is generally used both for mapping as well as engineering analysis including: hydraulic water pressure and distribution modeling and sewer time flow modeling. This type of analysis requires correct capture of connectivity and flow direction information. Minor errors such as a mistaken connection between two lines which in a typical GIS database would be inconsequential, would result in significant errors when the GIS database is used for example as the base for a pressure model.
GPS Field Inventory Collection
At the beginning of each day’s field work, which mostly takes place on the dusty shoulders of roads and highways running aside the water pipe rights-of-way, Thrasher technicians open the GPS Analyst extension running inside ArcGIS on a laptop computer to “check out” the data sets to be mapped. This means that the geodatabase files relating to those infrastructure features that will be mapped or updated are selected and uploaded by USB cable link from the laptop into the GeoXT handheld.
In the field, ArcPad displays a schematic of the water system assets that will be mapped. As the field crew finds each feature, an onscreen point-and-click menu generated from the data file assists the user in collecting the desired attribute information. As the crew member enters the descriptive data into ArcPad, the GPS receiver records 20 location points for each feature in less than a minute. This location data is stored with the other attribute data in the mobile geodatabase inside the
GeoXT handheld.
Finalization of Data
Once the field data has been collected, Thrasher overlays the new layer of water
and wastewater features on a digital orthophotograph. Many of the larger assets, such as pump stations, water storage tanks and meter vaults, are readily visible on the orthophoto. GIS specialists compare the location of the features mapped in the field with those visible on the ortho. They have now determined the accuracy of the data collection is well within the one meter mandated by the client.
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