Embedded Files
Problem:
Campus and Facilities Management at North Carolina State University has a series of CAD files created as part of the 2005 Master Plan for the campus. These CAD files do have no map projection and need to be georeferenced, converted into feature layer files and stored in a geodatabase for use in geospatial analysis projects.
Analysis Procedures
To solve this problem, I used the georeferencing toolbar and Feature to Polygon tools in ArcMap 10.7. The data used was a series of CAD files from the 2005 Master Plan provided by the Office of Campus and Facilities Management. This data was georeferenced to a 20-meter resolution orthophoto of the campus.
After importing the 20-meter orthophoto and the master plan data, I applied the appropriate coordinate system to the data frame. The master plan data was displayed by selecting polyline and polygon drawing layers. In order to easily identify desired features, I adjusted the symbology f to display the data according to the CAD feature “Layer” providing recognizable names in the Table of Contents. At this point, I was able to georeference the CAD data by aligning it over the orthophoto using the georeferencing toolbar. Once the images were aligned, I was able to update the georeferencing and the CAD data was precisely positioned and aligned with the state plane projection making it ready for export to the geodatabase.
I started with the first of the six required geodatabase layers, “Streets”. I selected this layer in the Drawing Layers menu and then exported the data using the data frame coordinate system. This created a polyline shapefile of campus streets in my geodatabase that had an appropriate coordinate system. This data did not need to be converted to polygon data. Several layers, such as “Buildings”, did require the data to be converted to polygons. For these layers, I utilized the Feature to Polygon tool to combine both the CAD polylines and CAD polygons with an XY tolerance of 0.5 feet. Through trial and error, I found this XY adjustment sufficed for closing any polygons that might be missing a few pixels without altering the overall polygon. Additionally, only for this particular layer, I combined existing and future buildings from the CAD data into one “Buildings” feature layer in the geodatabase during the conversion to polygons. This process of exporting data and converting it to polygons, if needed, was repeated for the remaining layers. The end result was a geodatabase consisting of three polygon layers and three polyline layers of the campus according to the 2005 Master Plan
Results
Click images for a larger version
Georeferenced CAD data shown over medium resolution aerial imagery of Western Boulevard with Main Campus to the north.
Georeferenced CAD data shown over light grey basemap of Centennial Campus at North Carolina State University campus
Georeferenced CAD data shown over medium resolution aerial imagery of the entire North Carolina State University campus.
Application and Reflection
Problem description:
CAD software is used throughout the engineering field for design and construction in both 2-D and 3-D. Converting CAD data to GIS data would be very beneficial in assessing changes to water infiltration and runoff rates. As a parcel of land undergoes development and redevelopment it’s important to know the areal extent of buildings and impermeable surfaces. As development occurs, aquifers receive less recharge from infiltration and erosion increases from greater amounts of runoff. Knowing the change in area of impermeable surfaces, soil types and average rainfall for the parcel can lead to highly accurate assessments required in urban planning, monitoring ground water and controlling surface water and potential flooding.
Data needed:
For a new site being developed, CAD files would be required for all structures being built including landscape structures. In addition, an analyst would want to incorporate a digital elevation model to calculate slope. Soil sampling or highly accurate soil maps would also be needed to determine infiltration. This type of analysis would also require averaged rainfall data from a reliable source. Ideally, these averages should cover at least a thirty year period and be average by month to account for seasonal changes and climatic cycling.
Analysis procedures:
In the first part of this analysis I would determine the amount of impermeable surface area based on building footprints and the amount of asphalt and concrete to be laid down. Using this number and the rainfall averages it would then be determined how much additional water will become runoff. Calculating slope would then allow for calculating the rate of flow and direction water will take across the surface. From this information it can be determined if water needs to be retained on the site or if there is a nearby body of water such as a stream that can accommodate the increase of rain water.
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