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surveyor's drawing in decimal units?


td88

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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

File to Cadtutor 4 20 09.DWG

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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

;; 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

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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.

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

Obviously it's not a strictly 2D dwg.

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... 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.

 

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.

 

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

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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

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).

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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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

 

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).

 

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.

 

lp,

 

Please be as critical as you want. This drawing was dropped in my lap and I'm trying to make sense of it. Git er done has been known to happen in my neck of the woods.

 

The problem is, when an old schooler like me views a "plan" with the smart points, as you're describing, I have no idea what I'm looking at. I might suggest there should be a new name for one of these "3D plans" just to give a heads up to us codgers, although, after today I will proceed with caution with surveyor drawings. Still don't quite know how you would measure A-B in the X/Y plane with the Distance command in one of these "plans".

 

Thanks to lp, dtkell and Profcad for the same day response on this. Mystery solved and back to work.

 

td88

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Hi,

Just took a quick look and maybe you'd best go back to the surveyors for an explanation.

Sorry, don't know how you get 1208 units I get Command: '_dist Specify first point: Specify second point:

Distance = 350.9708, Angle in XY Plane = 334.041, Angle from XY Plane =

359.858

Delta X = 315.5601, Delta Y = -153.6281, Delta Z = -0.8717

 

I've thawed all the frozen layers and found some sort of site section but what confuses me is that the horizontal distance between the gridlines is 100 and measures as such but although the vertical distance implies that it should be 10 it actually scales 100!

In addition a 3D view shows the A-B line is not in 2D (see Z=0.8717 above) so it is probably related back to the levels off the distorted site section view. I know that surveyors often use this technique of having different horizontal and vertical scaling (can't remember off-hand what they call it) but it's not helping!

 

Note that the UNITS are to 4 decimal places but the (levels in text) are rounded to 2 or even 1 place, and you have also got 2 dimstyles set (standard & arch-ft) Standard gives an A-B dim of 350.9697 and Arch-FT makes it 29' 3" interestingly 350.9697 rounds off to 351 and 29'3" is 351 (29x12+3). If you draw a line from A to B and list the properties of that line it gives a length of 350.9708 (see above) which when rounded to all intents and purposes is 351 (otherwise known as 29'3")!

 

Remeasure your A to B line and check your figures - see my extract above.

Maybe I'm wrong but if the distance between two points is 100 units it doesn't make any difference what those units are, - feet, inches, mm, light years it's still 100 UNITS.

 

all the best,

 

Rob

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Maybe I'm wrong but if the distance between two points is 100 units it doesn't make any difference what those units are, - feet, inches, mm, light years it's still 100 UNITS.

 

all the best,

 

Rob

 

Thank you, Rob, you've restored my sanity.

 

Here's what I got, when I ran the Distance command on A-B.

 

Command: '_dist Specify first point: Specify second point:

Distance = 1208.5337, Angle in XY Plane = N 64d2'28" W, Angle from XY Plane =

N 16d52'57" E

Delta X = -315.5601, Delta Y = 153.6281, Delta Z = 1156.4489

 

Another discovery I made today in the Cadtutor archive was, (some?)surveyors like to scale their drawings down to 1/12 size. When I scaled the drawing up 12 the dimensions made sense (in Arch. and Eng. units) and could be plotted at the scales I was attempting to use. Prior to that everything was Lilliputian.

 

td88

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I see you are on LT which may explain why your 'dist' command looks different to mine on ADT2006. But as long as you have a workable answer that is all that matters. Let's hope you get some sense out of your surveyor...SOON :roll:

 

Rob

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lp,

 

.... Still don't quite know how you would measure A-B in the X/Y plane with the Distance command in one of these "plans".

...

td88

 

You can filter out the Z elevation in any command. So in the Dist command, start DIST, use endpoint osnap, but before picking the endpoint type .xy, then pick the endpoint, now it will ask for the Z, just type 0, enter. Do the same thing on the other end.

 

Simpler way or at least another way is to use a simple pline and osnap the two points. Plines won't slope in the Z direction so listing or dimensioning it will give you just x and y.

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I see you are on LT which may explain why your 'dist' command looks different to mine on ADT2006. But as long as you have a workable answer that is all that matters. Let's hope you get some sense out of your surveyor...SOON :roll:

 

Rob

 

Sorry Rob, I can't claim that excuse. I'm using Acad 2006 full for this work. I switch back and forth (with drawing).

 

td88

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You can filter out the Z elevation in any command. So in the Dist command, start DIST, use endpoint osnap, but before picking the endpoint type .xy, then pick the endpoint, now it will ask for the Z, just type 0, enter. Do the same thing on the other end.

 

Simpler way or at least another way is to use a simple pline and osnap the two points. Plines won't slope in the Z direction so listing or dimensioning it will give you just x and y.

 

rkent,

 

Thank you. Thats what I call a solution. I always liked Albequerque.

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I have found this type of poor drawnig practice quite common with UK land surveys. I always look at the drawing in Isometric before attempting any works.

 

Unfortunately rkents suggestion of changing the Z values to 0 although in theory is what is needed, when the drawing is 100 times more complex, with curves formed from polylines 1000 points plus, I tend to reject the plan and ask the Surveyor to re-submit his drawing.

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Another simple method of finding the horizontal distance between the points A & B is to draw a line between them and then "list" the line. The length in the current UCS is shown as well as the 3D length and lots of other useful figures. :D

3DlineListed.jpg

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