Auto CAD Integration

9/25/14

Problem:

The scenario presented for the assignment centered around NC State University campus planning and facilities management and the development of a geodatabase for managing campus buildings and related facilities. The specific foci for the geodatabase were campus streets and sidewalks, Rock Branch Creek, lakes in the area, and current and future buildings. The data used for these analyses were provided by Dr. Perver Baran, GIS instructor at NCSU, including a 2005 CAD drawing of NC State campus drawn to scale but with no coordinate system and a 1999 orthomap of campus with the coordinate system of NAD_1983_StatePlane_North_Carolina_FIPS_3200_Feet. The geo-referencing tools provided by ArcMap were used to rectify the layers and import the layers into a file geodatabase.

Analysis Procedure:

To put the files into the same scale to faciliate the overlay process, coordinates may be projected in ArcCatalog for the CAD file into NAD_1983_StatePlane_ North_Carolina_FIPS_3200_Feet. While in ArcCatalog, a new File Geodatabase should be created. Using the georeferencing toolbar in an ArcMap document loaded with the pertinent data files, the CAD file can be aligned with the orthomap, and the individual features of the CAD layer of the map defined via the properties function. Georeferencing involves reliable, known anchor points that are likely to not change positions from year to year. The georeferencing tools available in the tool bar should be used to systematically rotate, shift, and scale the CAD drawing to the orthomap. Two control points per action are matched between the two documents, and the control point process repeated until a satisfactory alignment results. When the alignment process meets approval, a new world file is generated by clicking update georeferencing. New, appropriately coordinated shapefiles or geodatabase objects can be generated from the modified CAD data. Where required, these should be converted from polylines to polygons and the features of interest imported into the file geodatabase created earlier.

Figure 1. Workflow diagram to reference the CAD drawing with no coordinate system to the orthomap with an assigned coordinate system and produce a file geodatabase.

Results:

The CAD image was aligned manually using approximately 5 sets of control points. After alignment, the individual layers of interest - streams, lakes, athletic complexes, buildings, and walkways and streets specific to NCSU campus - were extracted from the CAD layer, imported into a file geodatabase (Figure 2), and a new World File was produced (Figure 3). The layers from the new geodatabase were imported into the ArcMap document, and a formal map was generated (Figure 4).

Figure 2. File structure of file geodatabase, Masterplan05.gdb

Application and Reflection:

The techniques learned in this section allow one to overlay and process layers of unknown coordinates with layers of known coordinates and produce an appropriately aligned new layer. For this assignment, we used a CAD drawing, but other image formats can be used as well. For example, in the process of generating the map of Eno River State Park (see Our Mushroom Hunting for the map and the supporting data), I wanted to create a layer with individual hiking areas and individual trail segments. Some geo-referenced data were available in shapefile format, including the state-owned lands that make up Eno River State Park and the major waterways that flow through the area, but there were no shapefiles I could find that contained the trails in the park. So, in order to produce my trail map, I identified a good data source, requested and received permission from the owner to use the data for my project, then captured screenshots. Having acquired the necessary information, I was able to import the image files into ArcMap and apply the techniques in this exercise to align the screen captures so that I could produce an accurate, geo-rectified layer for my trails. For the control points, I focused largely on river characteristics, including bends and stream intersections, to accommodate the alignments, as these are likely to be historically and spatially more correct.