Coordinate Systems in ArcGIS for AutoCAD; Is it morning already?
Traveling from the West Coast to the East Coast has its challenges for business. On my last trip I shared a hotel room with an associate at a large conference; My colleague, tired after a long day, was looking to get to sleep at 10:00 pm, which was 7:00pm my time. My 5 year old back home, wasn’t going to bed for another hour. My colleague then announces he would be getting up at 5:00 am (booyah!) and was asking if he would have a conflict with me getting ready in the morning. Quick calculation in my head… that’s 2:00am!The Earth is round, so even though we may have an accurate measurement that same measurement has a geographic relevance for a particular place. The watches on both of our wrists were accurately measuring the time in our zone. Trouble was I was out of my zone.
For many CAD related efforts I may be entering coordinates accurately in my zone, be it state plane or UTM or the alike. However, without some means to identify which zone I am in, or more basically what coordinate system my coordinates are depicting, when I am outside that zone things don’t line up.
In ArcGIS for AutoCAD you can identify which coordinate system you are in so that map services from other coordinates systems will automatically line up in the right locations. Likewise when the drawing is added to ArcGIS software it will also line up. By default ArcGIS for AutoCAD will assume that if you are adding a map service within an AutoCAD file without a coordinate system defined you will want your drawing to have same coordinate system as the map service. This may not be true; therefore you will want to select your coordinate system from a list of some 4000 coordinates systems that ship with ArcGIS for AutoCAD first. If your AutoCAD file has a coordinate system definition in an external .PRJ file, ArcGIS for AutoCAD can import that .PRJ file and store it inside the CAD file according to the Mapping Specification for Drawings.
For Microstation files and AutoCAD files not used in ArcGIS for AutoCAD you would copy a .PRJ file of the appropriate coordinates system in the same directory old-school.
posted by Don Kuehne at 1:09 PM
4 Comments:
When I add a map using the ArcGIS for AutoCAD toolbar, the map is just dark gray. I'm using AutoCAD Map 3d 2009. Any idea why?
If the map service is being projected and you are zoomed in far there could be some extreme scaling going on. I'd suggest trying ArcGIS Online maps in a new drawing to get something you know should work.
So I have AutoCAD .dwg map file floating in space arbitrarily. Is there a way that I can project it into a UTM coordinate system and georeference it to line up in the correct geographic space? Any hints?
If you are an ArcMap user you must first determine if the coordinates in the file are in UTM or not. If they are but ArcGIS doesn't recognize them you can add a projection file to the data with ArcCatalog (see the help.) Once in ArcGIS you can fit the data to existing GIS data if you know what at least two coordinates in the drawing file are supposed to be. Using the ArcGIS georeferencing toolbar in ArcMap you can interactively postion the drawing to fit the map. Using the snapping capability of ArcMap you can select two point on the drawing and their actual position on the map.
If you are an AutoCAD user. You can get the free ArcGIS for AutoCAD application and add the appropriate UTM zone coordinate system to your drawing using the ASSIGN Coordinate system tool and then use standard AutoCAD MOVE,SCALE and ROTATE tools to position the drawing correctly.
You can also read some of my old posts on the topic by going to the archive listed in the column to your right on this blog. Under the title "This Blog's Master Index".
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