COORDINATE UNITS AND POINT POSITION

[CADEngr2014]

Hello,

I created shape files from borings points that were in a file set to NAD83-US Survey Feet, inadvertently, should have been International Feet.  The base survey information I have for the project is in NAD83 International Feet.  So to check the shape files and their relative position based on the two different coordinate units, I imported the boring shape files into a file that was set to NAD83 International Feet and another file set to NAD83 US SUrvey Feet.  Then I xreferenced the file set to International Feet into the file set to US Survey Feet and did not see any difference in the boring point positions.  I find that a little puzzling that there was no difference at all between the boring points set to two different coordinate system units, such as International Feet and US Survey Feet.  I have to ask, does the Xref functionality in Civil 3D adjust for coordinate location automatically?  If so, how else could I test the relative position of these two point imports into two different coordinate units?

[ericcollins6932]

Sounds like the software is scaling based on what you told it. You need to lie to the software to see the difference. There something like a 2ppm difference so if the area is small, you won't see the impact.

[rl_jackson · Accepted solution]

No adjustments are made to the raw coordinates until a scale factor is applied to your data. Basically a coordinate is a coordinate C3D assumes you know what zone the coordinates it does not adjust them based on the zone. The same would hold true if you had metric coordinates that were imported in a US Survey Feet drawing it wont change the value but your geographic location will be incorrect.

[wfberry]

That's what I thought, but when I xrefed a metric to either an imperial or an international foot, it applied a scale.  Applying international xref into an imperial did nothing.  

In my case I am over a million 300k feet from 0,0 so any small scaling should be readily visible. It should be about 3' or so. (inter. vs imperial)

Bill

[AllenJessup · Accepted solution]

Bill,

Xrefs -like blocks - are controlled by

INSUNITS - The base units in the drawing

INSUNITSDEFSOURCE - The assumed units of a source drawing that doesn't have the base units set.

and

INSUNITSDEFTARGET - The assumed units of a target drawing that doesn't have the base units set.

This doesn't affect cogo points in any way. As you've noticed these defaults know nothing about US Survey feet.

Allen