Thursday, November 5, 2009

What Is Wrong With My Hatch?

Have you ever had a hatch pattern display incorrectly? If you are using a hatch pattern like gravel or concrete the sides of the intended shapes within the hatch may not line up properly. Giving you results that don’t look at all like your desired hatching. This typically happens when the area that you are hatching is very far from the origin (0,0) of your coordinate system. In civil drawings moving the objects or changing the location of the origin is typically not an option because it would destroy the coordinate system of your drawing.

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  1. Hatch is not displayed correctly is just one problem you have. At this moment you actually have lost AutoCAD accuracy.
    AutoCAD has reach the floating points capabilities, and you may not get the result correctly when you draw any objects. You may reduce the effects by using 64bit version that can handle larger floating points.
    OR... you can choose other unit so you don't need to use so many digits in your coordinate (m or km).
    The other way is using local coordinates to avoid large coordinate. Drawing so far away from 0,0 is a no-no.

  2. The problem I described here has nothing to do with drawing geometry accuracy, it is related to the relative imprecision used to define some complex hatch patterns. When used close to the 0,0 origin, little precision is required to define them. However, when using state plane coordinates (and other large integer coordinate systems) that civil engineers and surveyors have routinely used in AutoCAD for decades to accurately locate objects in the real world, tiny rounding errors in hatch pattern definitions can accumulate to the point where the patterns no longer display properly. This is why Autodesk added the two system variables HPORIGIN and HPORIGINMODE in the 2006 version of AutoCAD.

    Your comment does bring up another important issue within the industry, that Architects and Civil Engineers/Surveyors still have difficulties communicating and sharing drawings that go beyond just using different units. There needs to be an understanding of the necessity of using a real world coordinate system. Solving this certainly goes beyond the scope of this article or this blog, however, I might suggest that it could start in many cases with an effort on both sides for better communication and understanding of the others industry. If you would like to learn more about Civil 3D or Map 3D I would suggest taking a look at some of our books.