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  1. #1
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    Default surveyor's drawing in decimal units?

    Just received the attached surveyor's drawing. It's in decimal units. When I measure from point A to point B, I get an answer, which states 315 units in the X direction and 153 units in the Y direction but, the "distance" is shown as 1208. units. I would have assumed the distance is the hypotinuse of the X and Y sides of the right triangle. The measurement, also, states there is an angle "from" the XY plane of 16 deg.'s.

    I would have expected a plan view surveyor's drawing to be 2D with a 0 angle from the XY plane and, also, expected the decimal measurement to match the numerical amount of the Architectural or Engineering. For example if the Arch. units measure 100', the Decimal would measure 100 units or, possibly, 100' x 12" or 1200 units.

    Could someone look at the attachment and offer an explanation?

    Thanks,

    td88
    Attached Files

  2. #2
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    If you ID the endpoint at A, it has a Z value of 0, B has a Z value of 1156.4489. You're getting the slope distance, not the horizontal distance.
    This will return the horizontal distance
    Code:
    ;; returns horizontal distance regardless of z values LPS 2008
    (defun c:di (/ pt1 pt2 pt1-flat pt2-flat hd hdtxt)
    (setq pt1 (getpoint "\nHorDistance  Pick first point: ")
          pt2 (getpoint "\nPick end point: " pt1)
          pt1-flat (list (car pt1) (cadr pt1))
          pt2-flat (list (car pt2) (cadr pt2))
          hd (distance pt1-flat pt2-flat)
          hdtxt (strcat  "\nHorizontal distance = " (rtos hd 2 2) "'")
    );setq
    (princ)
    (prompt hdtxt)
    (princ)
    );defun
    Last edited by lpseifert; 20th Apr 2009 at 09:27 pm.

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    I know you know what that means, lp, but, I need to know what that means. First off, I thought the Z distance is the distance forward and back from the picture plane, as in the third dimension in a 3D drawing. It seems to be saying it is tilted from the XY picture plane 16 deg.'s.

    When you say the "slope distance" are you referring to the decimal equivalent of degrees of angle? I don't know the term "slope distance". From where to where?

    Why does a 2D drawing have Z value at any point?

    Thanks,

    td88

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    When you use Acad's Dist command, you're getting the distance between two 3D points. In your dwg the endpoint of the polyline at Point A has coordinates of X = 5726.4109 Y = 2689.3770 Z = 0.0000; Point B has coordinates of X = 5410.8508 Y = 2843.0051 Z = 1156.4489. So you were getting not only the distance between the X.Y coordinates but also the distance between the Z coordinates.
    Quote Originally Posted by td88 View Post
    Why does a 2D drawing have Z value at any point?
    Obviously it's not a strictly 2D dwg.

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    Senior Member dtkell's Avatar
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    Quote Originally Posted by td88 View Post
    ... Why does a 2D drawing have Z value at any point? ...
    Put simply, surveyors work in the real world and all points found in the real world have an elevation (z value).

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    Obviously it's not a strictly 2D dwg.[/quote]

    lp,

    So far, you're re-stating my suspicions about the drawing back to me as fact.

    What I'm attempting to find out is why a surveyor would create a 2D plan view, which includes Z values greater or less than 0. I thought it might be something I misunderstood ot hadn't encountered with survey practice.

    Do you know if all 2D surveyor CAD drawings are drawn as if they're 3D, with positive and negative Z values? I don't understand the value of that, if you continue to call it a plan. In my experience, and I'm willing to be wrong, a plan, by definition can not be 3D.

    td88

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    lp and dtkell,

    Simply put, another way, how does one go about measuring the disance A-B in my drawing, in the X/Y plane?

    td88

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    I ran the FLATTEN command on the drawing and it is now in 2D and it should give you the 2D information that you need.

    Some of the objects had different Z values.
    Attached Files
    John Helton
    Professor of CAD
    Oklahoma City Community College
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  9. #9
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    Quote Originally Posted by profcad View Post
    I ran the FLATTEN command on the drawing and it is now in 2D and it should give you the 2D information that you need.

    Some of the objects had different Z values.
    Profcad,

    You read my mind. I never use Acad 3D and attempted to view the drawing in 3D (clicked View/3D/Left) hoping to gain an understanding of what was going on. When in 3D, I wondered, now that I'm in 3D, how do I get out. Is FLATTEN the answer?

    td88

  10. #10
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    I'll try not to be overly critical because I don't know the circumstances of the source dwg, but after a quick look the dwg is pretty sloppy
    Quote Originally Posted by td88 View Post
    Do you know if all 2D surveyor CAD drawings are drawn as if they're 3D, with positive and negative Z values?
    If a field crew carries elevations when doing a field survey the downloaded points will have a Z value. If the cadd tech draws (p)lines from point to point, they will have elevations other than zero. If they draw feature lines not snapped to points, they will most likely be at elevation zero. Git er done mentality; depends on the tech (and if the boss is breathing down his neck).
    Quote Originally Posted by td88 View Post
    I don't understand the value of that, if you continue to call it a plan. In my experience, and I'm willing to be wrong, a plan, by definition can not be 3D.
    Consider a topographic plan; the contours are normally drawn with polylines with an elevation assigned. When you view it in Plan (top) view, it all looks 2D.

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