Units Issue: file units (inches) vs. georeferenced image units (feet)

[Anonymous]

I am trying to georeference survey data and place it in the correct geographic space by aligning it with an orthophoto.

I have set up my base file to have the following:

Units: Architectural, Inches

Coordinate System: NAD 83, Indiana State Plane-East, Feet

The workspace: "Tool-based Geospatial" (so, I am using the Map 3D workspace of my Civil 3D 2010 program)

The orthophoto is from the state of Indiana and is in that same coordinate system: NAD 83, Indiana State Plane-East, Feet

I brought in the orthophoto using the Task Pane, following this: Data > Connect to Data, and then going to "Add Raster Image or Surface Connection"

I actually have three orthophotos, and they do align properly next to each other to show the entire area I'm working in.

THE PROBLEM:

The orthophoto is too small by a factor of 12, which tells me it is displaying as if it's in Feet, not Inches. I thought the computer would automatically scale it correctly to my file's units when I used this "data connect" method. The survey file units are in Decimal Feet, and when I copy and paste in the survey data, it is the same scale as the orthophotos. I do need the survey data to match the scale of the orthophoto, so that's fine... except.... both need to acknowledge the units of the base file.

I cannot simply scale up the orthophoto because then it would not be in the correct geographic location!

How do I get georeferenced images and some cad data to see my file units?

(by the way, Architectural-Inches is the standard around here and this is what the client is requesting.)

Please help!

Thanks,

Anna

[parkr4st]

I downloaded a photo from Indiana GIS.  I data conected to a blank map and it set the GCS to IN83-EF with units "feet" as it should.  If this works correctly you have a base map and save it.  Put your survey file into the map.  You didn't mention its format so presume it is dwg lines, points, etc? not a .shp or other file format?  If it lands on top of the photo where it belongs to scale then it becomes part of the base map. If not, scale it to fit the photo and save it.  If loction is critical use ground points to scale to .

If I do this and am not sure if it is correctly geo located I mapexport a .shp and load it into GPS and verify on the site it is correct.  If the site is to far to drive to, put in a local photo where your are and draw a few test points and make sure the GPS gets you there.

As for"Architectural-Inches is the standard around here" perhaps it is time to change the standard? 

Can you fill in what the Arch inches will be used for.

Dave

[Anonymous]

Parkr4st,

What do you mean by "as it should be"???

Can I NOT set my base file to Inches and have the georectified image scale properly to my base file as it comes in?

Is it some strange requirement that I must set my base file to be whatever the ortho is?

Also, if I understand your process, it is exactly what I have already done, with the exception of the units of the base file. The survey (a dwg file) that I brought in is in Feet, and so is the image. When I line up the survey cad data with the image, they are the same size, which is not a surprise.

The problem is that neither one is scaling to the units of my base file. Is there a way to do this?

thanks!

anna

[parkr4st]

What do you mean by "as it should be"???  What I mean is if the software is working correctly the coord system will be that of the world file unless you set coord system beforehand.  Sometimes this does not happen because map does not read the world file.

As far as the units, the map is 1:1 like all dwgs.  1 inch  = 1 inch   1 mile = 1 mile etc.  zoom in to 1:2 scale and measure a pixel.  the pixels are 12 inches or 1 foot square. 

new dwg.  units to Arch inches.  _mapiinsert command and insert the photo.  it will measure 5000 inches square (416.666667 ft)   _mapiinsert again but this time set the scale at 1:12 and units for insertion point and density to feet and the photo comes in at 5000 feet square (dimension will 60,000 as in inches because that is the units.  and you will notice that the coord sys is none because the world file was not read and the photo is not georeferenced.

Different behaviours based on the two methods of getting the photo into a map.  data connect vs. mapiinsert.

In83-EF you can draw in feet, georeferenced,  in the second case you can draw in arch inches but not georeferenced.

If you draw a building footprint on the second map and mapexport to a sdf, data connect that in the first map the object can then be moved scaled and rotated as a sdf feature and checked in.  the sdf is now georeferenced on the first map.  the accuracy of the m,r,sc is proportional to ground control of course.

Some others may add to the topic and help clarify what is happening.

dave

[Murph_Map]

Look up in the help files these varibles "INSUNIT , INSUNITDEFSOURCE, and INSUNITSDEFTARGET"