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Member
brake76
Posts: 3
Registered: ‎12-22-2011
Message 1 of 6 (261 Views)

Unit issues with georeferenced images

261 Views, 5 Replies
12-22-2011 10:57 AM

I am an autocad and ESRI user who is trying to better intergrate the functions with Map 3d.  I am having problems with drawing units when connecting to GIS data.  I live in TN, so I have set the coorinate system to TN NAD 83, Feet.  When I connect in a NAIP aerial, it displays properly.  When I measure anything, however, the distances are off by a factor of about 1/3.  That is, something that is supposed to be 18' is measuring 6'.  I have played with the units, but can't seem to come up with an answer.  Any help would be appreciated.

 

Thanks,

Valued Mentor
Posts: 376
Registered: ‎03-24-2004
Message 2 of 6 (257 Views)

Re: Unit issues with georeferenced images

12-22-2011 12:45 PM in reply to: brake76

metric?  3.281 feet = 1 meter

 

dave

Member
brake76
Posts: 3
Registered: ‎12-22-2011
Message 3 of 6 (255 Views)

Re: Unit issues with georeferenced images

12-22-2011 12:53 PM in reply to: brake76

That thought did cross my mind.  I have played with the different units coordinate systems,  and nothing changes.  Here is the only pertinent information from the USDA image metadata:

 

patial_Reference_Information:
  Horizontal_Coordinate_System_Definition:
    Planar:
      Grid_Coordinate_System:
        Grid_Coordinate_System_Name: Universal Transverse Mercator
        Universal_Transverse_Mercator:
          UTM_Zone_Number: 17
          Transverse_Mercator:
            Scale_Factor_at_Central_Meridian: 0.9996
            Longitude_of_Central_Meridian: -81
            Latitude_of_Projection_Origin: 0.0
            False_Easting: 500000.0
            False_Northing: 0.0
    Geodetic_Model:
      Horizontal_Datum_Name: North American Datum of 1983 (NAD83)
      Ellipsoid_Name: GRS1980
      Semi-major_Axis: 6378137.0
      Denominator_of_Flattening_Ratio: 298.257222101

 

I didn't see anything about units.  Anyone know if the UDSA aerials are in metric, and if so, how to correct this?  I have sucessfully connected to shapefiles and google earth images, so I am pretty sure it is something with the aerial itself. 

 

Thanks,

*Expert Elite*
Murph
Posts: 1,867
Registered: ‎11-13-2006
Message 4 of 6 (250 Views)

Re: Unit issues with georeferenced images

12-22-2011 02:54 PM in reply to: brake76

brake76 wrote:

.  Anyone know if the UDSA aerials are in metric, and if so, how to correct this?  I have sucessfully connected to shapefiles and google earth images, so I am pretty sure it is something with the aerial itself. 

 

Thanks,


IIRC some of the images from USDA are in metric even when the metadata states otherwise. Where abouts in TN are ya?

Murph
Supportting the troops daily.
Distinguished Mentor
thepworth
Posts: 525
Registered: ‎03-02-2011
Message 5 of 6 (247 Views)

Re: Unit issues with georeferenced images

12-22-2011 03:47 PM in reply to: brake76

USDA is metric.  Are you using FDO or MapIINSERT?  make sure you set the drawing coordinates to metric if using mapiinsert.  fdo will transform, mapiinsert wont... you need to insert in metric and perform a drawing query to transform utm meters to nad feet if not using FDO...


C3D 2011
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Member
brake76
Posts: 3
Registered: ‎12-22-2011
Message 6 of 6 (228 Views)

Re: Unit issues with georeferenced images

12-27-2011 07:51 AM in reply to: brake76

I have tried using mapiinsert and connecting to the SID file via the task pane (connect to data) and get the same result.  When I connect to shape files that weren't provided by USDA, everything comes in to scale and in the right location (even if i created the shape file in ArcGIS drawing on top of a USDA aerial).  Both image and shape files directly from USDA come in scaled to metric and in the wrong location.  I have never had these problems in ArcGIS.  Any ideas?

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