Exercise 4: Data Conversion and CAD GISC 6382 UTD Briggs 2/14/07Exercise 4Exercise 4: Data Conversion and CAD GISC 6382 UTD Briggs 2/14/071. Use Windows Explorer or ArcCatalog to copy CAD folder from P:\briggs\g6382\Exercise_data\to c:\usr\CAD2. Open ArcCatalog and go to CAD folder: each CAD file is a shown as a “group layer” Click the expansion box next to KEY832.DXF Note the multiple layers Preview the KEY832 CAD drawing layer ( icon) --this is the entire CAD drawing displayed as it was intended in the CAD system with designated line colors, width, shading etc..)--the CAD file displays in GIS environment without conversion--altho some features are differentiated by color, others are not (e.g. roads and city boundary)--try to preview table: there is no underlying table since it’s a CAD drawing file Preview KEY832 CAD feature layers (blue icons , , etc ) --preview the geography of the point, polygon and polyline layers: there are problems--point is empty, as is multipatch (in this case)--the polygon layer mixes together airport, lakes and parts of city boundary --the line layer mixes roads, railroads, city boundary --preview the tables of the polygon and polyline layers--the Layer variable differentiates features—this is key to display and convert CAD files--other variables all relate to display characteristics--not a feature characteristics database--however, sometimes these can be useful in identifying one feature from another--the same feature type (e.g. city boundary and lakes) is both line and polygon!--preview the geography and tables of annotation layer--it’s a separate layer not tied to the features being labeled other than thru proximity--all features (roads, airports, etc) are mixed together3. Establishing Real World Position and Setting the projection for the CAD Dataset Before proceeding with using CAD data it is wise to first be sure that you have “real world” positioningand that the projection system is defined. This is a two step process3.1 Create a CAD “world file” to reposition the data to its true world position. This is done using the Georeferencing toolbar. See georef.doc #5 which we covered previously. Some CAD data sets are already in “real world” position, which is the case here, as we shall see in a moment. Consequently, this step is not needed here.3.2 As with any geographic data set, we also need to define the coordinate system. Most commonly, CADdata for local areas in the US is in State Plane. To ensure that they are properly handled by ArcGIS we can create a .prj file to “define” this projection. However, you do not do this with the standard DEFINE tool. You do it in ArcCatalog. However, let’s first check the actual projection using ArcMap.Open ArcMap and bring in the CAD file KEY832 —what do you think is the projection?- Look at the coordinate values. What is your guess? - Add another data set with that same projection and see if they overlay, for example, P:\briggs\g6382\DataSets\Coverages\rdstr95. Does it overlay? Yes. o What is its projection? Use Properties/Source tab: it’s State Plane, NAD83, Feet.o If it does not overlay it means  you guessed the projection wrong  or its not in true world location for that projection,  or both!Open ArcCatalog and go to the CAD file. We will define its projection. 1o Right click CAD file and select Properties/Coordinates. This tells us about the world file. It says that there is no world fileNote the From and To coordinates. They are the same. These are read from the world file. When the values are the same, as here, it usually means that there is no world file. In this case, a world file is not needed since the coordinates are already in true world location, as we just showed in ArcMap. Now we define the projectiono Right click CAD file and select Properties/Spatial Reference. o Click Edit button and Import projection from rdrstr95o Click Save As button, navigate to the folder containing the original CAD file, and specify a file name the same as the CAD file name A .prj file should be saved (check in Windows Explorer)o In essence, you have carried out a “Define” for a CAD data set4. Using CAD data as Feature Layers in GIS mapsOpen ArcMap, bring in the KEY832 CAD group layer. All the feature layers are brought in , but not the drawing layer.--they are displayed as they would in the CAD--the “CAD unique entity value” is used for display (see Symbology below) You may bring in the drawing layer separately if you wish--It will display identically to the feature layer as a whole.--however, individual point, polygon, line layers are not accessibleNote differences from standard GIS format:Polygons are replicated within the polylines--turn off the Polygon layer. Nothing changes. Turn it back on.--turn off the Polyline layer. The Polygons alone are presentLayers contain different feature types--turn off Polyline layer. Note how polygons are both lakes and airportsWe cannot turn off/on a single class of features--cannot just turn lakes on/offNote how CAD features are differentiated: Right click on Polyline layer and go to Properties/SymbologyNote the “Category” used: CAD unique entity valueThe CAD layer is “rendered” (displayed) by combining identification information from theCAD Layer variable, with display information (color, line width, etc.) from other CAD variables.You may modify the display color and styles by right clicking in the Symbol windowe.g. to modify red line, select Properties for Selected symbols--make it a wide red line--note how freeways and airports are effectedBasically, we need to separate out each class of features which are intermingled in the CAD points, polygon, and lines layers. We do this by processing the variables in the CAD table (usually the Layer variable)—at least three ways, all accessed via Properties Apply Symbology to one or more variables(usually the Layer variable)--can show multiple layers, differentiated by color/patterning2--or can limit display to one or a few layers--however, cannot turn individual layers on and off easilyUse Drawing Layers tab (unique to CAD)--allows you to select specific values on the Layer variable --displays only a single layerBuild a Definition Query to select features meeting a specific set of criteria--can use multiple variables for selection (e.g Layer and Text)--use of the text, color, width, etc.