Gretchen, If you use the Universal Translator, isn't there a button on one of the DWG conversion dialogs that let's you specify the coordinate system of the incoming data? (This assumes that you know what coordinate system was used by the surveyor, and that they used a standard one.)
If you don't know what system they used, then you have to make some guesses. One techinque I use is to display a map of the area using data I have already and know is right, and then I flip through the various likely projections and look at the coordinates that result in my map area. Then I look at the CAD file coordinates (you may have to first translate this file using non-earth feet, but even though that's not the right projection it lets you see the coordinate values) and when I find a projection that would result in coordinates like what I see in the CAD file, I re-translating the CAD file using that projection. That usually works, but you do need to have some idea as to where the files should end up relative to your control data as a check to make sure it worked. Ideally, the surveyor digitized one or more official NGS benchmarks in the CAD files (if they didn't, they should be drummed out of the League of Real Surveyors) and of course you also have a set of these control points for your area, so if the worst thing happens (the surveyor used an undocumented local grid system) you can just select all the data and drag it so that the control points line up. The lack of embedded coordinate systems information is one reason why I think CAD should never be used for making maps. Not for any intrinsic flaw in its ability or accuracy, but becasue there's hardly anyone who uses it who has a clue about map projections and coordinate systems, and consequently a lot of tedious work goes into making drawings that are nearly useless as GIS data sources. - Bill Thoen On Thu, 14 Jul 2005, Town of Hampden wrote: > Hi List, > > I searched the archives and found some useful > information, but I can't seem to get things to work > properly. I don't have a budget to buy those extra > tools at the moment like the one suggested at > http://www.icsinger.de/flxmap_e.htm or the > VisualHelmert thing with the broken link. > > What I'm trying to do is convert AutoCAD .dwg files > into MapInfo Pro .tab format. The .dwg files are > detailed soil survey maps that someone before me > apparently digitized? using CAD. I can't locate a > file anywhere on the Maine Office of GIS or at USGS or > anything. . . Regardless, surveyors send the town CAD > files of subdivisions all the time, so I need to get > this down. I understand CAD doesn't come with > projection ("non earth coordinates, meters") and I > have tried three things: > > First, I tried the Register Vector Tool (only 3 > control points??), but that brings my machine to a > grinding halt once I get the option to save (it's a > 2GB RAM machine with 500GB hard drive, dual Xeon > 3.4GHZ processors). . . > > Second, I tried what many people suggested in the > archives, which is to export the .dwg as a .mif file > and open it in notepad and change the Coordsys line. > I looked in the MapInfo user guide and where it > describes export options as either Save Window As or > Save Copy As .mif isn't an export option. So I took > this to mean use the Universal Translator. To figure > out the Coordsys line of the files that I already > have, in UTM, Zone 19 (NAD83), I used Universal > Translator to convert like so: > .tab -> .shp > .shp -> .mif/.mid > opened .mif in notepad > Coordsys line is: > Coordsys Earth Projection 8, 74, "m", -69, 0, 0.9996, > 500000, 0 > > So then I take the .dwg in the Universal Translator: > .dwg -> .mif/.mid > open in notepad and changed Coordsys line to above, > saved changes > .mif/.mid -> .shp > .shp -> .tab > > This doesn't work, because when I open the soils layer > and my other layers, it does the bad projection thing > of having two tiny black dots far apart from each > other when I do View Entire Layer-All Layers :-( > > Third, I tried using the CoordSys Bounds Manager tool > to set the coordinate bounds of the soils layer based > on the coord bounds of my reference layer. Didn't > work. > > Oh, and I also tried just converting .dwg to .tab and > then doing a Save Copy As and setting the projection > but I realized after doing so that MapInfo won't know > where in UTM, Zone 19 to assign my data, since it has > no coordinates. > > So my last thought was to save a .jpg screen print of > the window and open it and register the image? It > would be nice to not have to do this for every CAD > file the town will receive from here on out. > > Thanks to anyone with enough patience to give me a > little extra help- sorry I am such a beginner. In > such an Arc-dominated area, using MapInfo basically > means I'm teaching myself. Thanks again :-), > ~Gretchen > > > > > > Mapping/GIS > Town of Hampden > Hampden, ME 04444 > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! 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