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VW Math Errors, VW Bad at Coordinate Geometry?

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RE: VW 10.1.0, Win XP

I have used AUTOCAD to do 2D coordinate geometry (COGO) for land surveying. I HAD hoped to do the same with VW. But... VW does something bad, approximate and irritating that makes it useless for COGO. It makes terrible round-off errors.

I've got all snaps off, linear and angular "units" set to maximum accuracy (lotsa

zeros). I've set angular units to "degrees, minutes and seconds.

Say I want to draw a line of a certain length, at

a certain angle (a very basic thing to do in

land surveying, it's called a one course of a

traverse -- a traverse typically containing

dozens of courses)

Hit the line tool. Click the mouse anywhere on

the screen. The beginning point of a line is set.

Now set the angle:

Tab over to the angle entry box box on the data display bar. Enter "-89d59m26s" in the angle entry box. Hit return. Angle Data is accepted


Now to set the length:

Tab over to the "L:" (length entry) box on the

data display bar. Enter "30.00000" Thus far, so good. Hit the return key. DATA IS NOT ACCEPTED CORRECTLY !!

Upon hitting the return key, the "30.00000" is CHANGED by VW to "30.0117235714" !!! (This also

is what shows up in the object info palette).

Now, look, I just SPECIFIED 30.00000 -- what gives with VW throwing in an additional 0.0117235714 ? A rounding error of 1 in 3000 is


Interestingly, if I key in the same angle, but

change the length from 30.00000 to 3000.000 --

VW STILL changes the length I entered from 3000 to 3000.000177649 - an acceptable degree of rounding error 1 part in 30 million or so.

I also note that, depending upon the initial point of the line, VW gives me back slightly

different answers.

I also note that no matter what I do up in the

data display bar, I can't keep VW from CHANGING

the entered data and I can't get it to leave

my length of 30.00000 ALONE. Plus, while I can't

get the data display bar to accept 30.00000, I

CAN, once the object is entered, go to the object

info palette, set how it displays a line object

info to "angle and length" and change the funky 30.0117235714 BACK to 30.00000.

What is going on? Is there ANOTHER "units" or round-off parameter to VW I can set to get more

numerical accuracy?

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I'm not getting that when I try using VW 10.5.1

One thing you may want to do first is update to VW 10.5.1 and try it there.

What unit are you using ? (feet, inches, meters, etc.)

Are you on a MAC or PC ?

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I'm on a Dell PC (P4, 2.4 Ghz, 768 Meg RAM)

and using feet. The initial coordinates of the

point are, oh say, x = 8,500.00 and y = 10,000.00. Then go 30.00' from there.

I will try 10.5.1 if/when I get over various

time critical projects.

An added point -- it would be nice if VW allowed

angular accuracy to be input/displayed consistently in units more accurate than seconds

of arc -- say hundredths or thousandths of a second at least.

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It is usual practice when doing least squares adjustments of surveyed coordinate points to attempt to keep all the coordinates positive and

in the same quadrant. (Upper right, "North East"). Tis also common to run a traverse around

a section of land, one mile square. In this case, my control point was the Northeast corner of a section. A section is roughly 1 mile on a side, 5280 feet more or less. (But only more or less). In such a case I typically assign the Northeast corner the arbitrary coordinate of (10,000.00, 10,000.00), thus assuring that all coordinates of points within the section are positive. I'm required by statute to run

traverses to accuracies of better than 1 in 20,000, and typically by contract to accuracy of

better than 1 in 100,000.

My layer scale is 1:2400, 1" = 200'.

The above is nothing unusual -- a random land surveyor on any given day will run traverses

much larger and more accurate.

If the layer scale actually has an influence ( I

can't see why it would, but if it DOES.... well)

I suppose that for COGO purposes, it wouldn't bother me to set it to 1:1 (although I'm not sure

if VW would choke on the required paper size -- not

that I'm planning on printing anything out at that scale !! )

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