GIS --> CAD scaling problems

[Merissa Wilson]

We are having trouble getting our GIS data (in NAD27) to come into the right scale once we have converted it and xref'd it into our CAD drawings which contain aerials in NAD83. Any suggestions?

[GuthCAD Software Support]

Hi Merissa,

The only obvious suggestion is to be aware of the existence of the projection utility in the Arcv2CAD Settings dialog, i.e. for conversion of Lat/Long to UTM WGS84/NAD83, and check that matching output units have been selected (i.e. matching to the units in your CAD file.)

Do a translation of a very simple test file with a couple of points with known coordinates, so that you can check that the translation and XREF insertion have gone as expected.

best regards,
Software Support

[Merissa Wilson]

Each time we change the setting to do a Lat/Long to UTM conversion and try to save it that way, a dialog box pops up saying:

The currently selected Projection (Lat/Long to UTM WGS84/NAD83) is not suited to data values for this file. Reason: Longitude values > 180 degrees not allowed. Setting Projection to none. (and then we have the option of accepting that or canceling the save)

But it doesn't seem logical that you would need to convert from Lat/Long anyway, because both the GIS file and the CAD file we're trying to get in are in NAD not Lat/Long.

Any other ideas?

[lisak]

Merissa,

Have you heard any other solutions to your problem? We have the same issue in our office. I use GIS, most of my data is UTM, NAD83, 13n, whereas our client has created a custom projection for his site. I have reprojected the GIS data to his custom projection. Still, when I use Acrv2CAD 5.0, my dwg does not line up with the CAD dwgs. I have tried it with my data as UTM and it also does not work. I am not a CAD user so I am having a difficult time figuring out the language to use to describe how the dwg is not scaling.

Lisa :confused:

[Merissa Wilson]

Lisa,

We did not get any further on this issue, although we are having some in-office training next week from a GIS specialist and hoping to get to the bottom of it. When we asked him what software was best for converting the GIS data to CAD he said AutoCAD Land Desktop. We already have this software so will be learning how to use it for converting the data next week.

mw

[GuthCAD Software Support]

Hi,

Just a couple of things to check when data does not line up:

As far as Arcv2CAD goes, it simply uses the coordinates that are contained in the shapefile. Most shapfiles contain coordinates in Lat/Long degrees. So for example a point with coordinates 32.783 degrees N, and 96.8 degrees W (Dallas,TX) will be translated by Arcv2CAD to AutoCAD as a point with X,Y coordinates -96.8,32.783.

To see whether your shapefile data is in Lat/Long degrees or whether the data is already projected, look at the 'Info area' of the Arcv2CAD dialog box. It will show the X,Y,(Z) ranges of the data in the shapefile. If the data is in Lat/Long degrees then by definition the Longitude (X) values must be in the range -180 to 180, and the Latitude (Y) values in the range -90 to 90. See attached pic.

Arcv2CAD also supports the common projection 'Lat/Long to UTM WGS84/NAD 83'. If this projection is selected (UTM Zone 14N for the example point), and the units selected is meters, then the example point would be transformed by Arcv2CAD to the AutoCAD point with X,Y coordinates 706037.55,3629373.18.

A useful online utility for one-off data coordinates conversion is here: (http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html)

As a starting point if your data does not line up, check:

1. Is my shapefile data already projected or not?
2. If I have selected the 'Lat/Long to UTM WGS84/NAD 83' projection, did I select the correct units?
3. Is my projected data uniformly shifted with respect to the data I am trying to line it up with? A common situation where that may occur is that an offset is applied to make data easier to work with. Using the example point above an offset of -706000, 3629000 might be applied by the end-user so that they can work with smaller numbers. To get your data to line up in that case you need to perform the reverse data shift in AutoCAD (or if it is indicated that it would be useful for other users we will consider putting an option into Arcv2CAD itself to do this.)

Software Support