Hatch Area Reliability

[john.uhden]

I work with a Cad wizard who tells me that many hatches do not report a correct area.  Now I know that hatches that touch themselves report no area, but I have not been aware of any other hatches that report an incorrect area.

Is my Cad wizard correct, and if so can you describe what conditions will create an erroneous area?  One that he mentioned is allegedly due to trimming a hatch.

[pendean · Accepted solution]

@john.uhden hatches are not closed PLINE outlines substitutes, and can have holes, trims and overlaps and other easily-missed things going on for the average user to observe.

Are you a use-whatever-I-see-and-assume-it-is-perfect sort of AutoCAD user, or are you the trust-but-verify sort of drafter that likes to double-check everything?

[R_Tweed · Accepted solution]

I would not trust hatches, certainly not ones created by someone else using bhatch.  You would have a better chance of a correct area breakdown using regions or as  check hatches created from regions as a check.

[paullimapa · Accepted solution]

Come to think of it anything drawn in AutoCAD could be off even if you drew it yourself.

Best thing to do would be to double check to make sure the hatch covers the area you want to get an accurate area value. But when drawn correctly and AutoCAD does provide an area read out on the Properties palette when a Hatch is selected, that is the correct area.

[john.uhden]

@pendean ,

I am not very trusting when it comes to creating data that will be reviewed.  The embarrassment and damage to your reputation is not worth saving a few minutes.

[leeminardi · Accepted solution]

@john.uhden 

I created the shape below using a spline and the CV method.  Properties show the spline area as: 15.65269801

Hatching the shape using the pick point inside yields: 15.65296417

A difference of 0.0017%  

Close enough?

[john.uhden]

@leeminardi ,

Of course it's fine, but I don't think that new wing shape is gonna fly.  😳