12ft x 12 ft tarp (3d sketch + surface) please help.

[crmayo]

Hi all,  I'm hoping someone can help me draw this part.  Attached is a start in Inventor 2012.  I also have Inventor 2013.

The tarp is 12ft x 12ft at the corners.  It tapers down hill on two corners by 3.5" as shown.  I used splines and just moved points to get the shape you see now.  It's not constrained.  The problem is the shape isn't accurate.  By moving the point straight down 3.5" it don't take into account the slope of the line and now my 12ft corner dimensions are no longer correct.  Does anyone know how I can make part dimensionally accurate like this?

Thanks for your time,  Chris

[JDMather · Accepted solution]

The easiest way to create, and especially control, a 3D sketch for something like that is to start from 2 2D sketches.

http://home.pct.edu/~jmather/content/DSG322/Inventor%20Tutorials/Inventor%2011%20Tutorial%207.pdf

This is a bit different than yours, but I would do a 2D sketch of the Top and Front views and find the 3D intersection.

[crmayo]

Thanks JDMather, that did the trick.