inverse curve

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dale elsen
Posts: 14
Joined: Thu Nov 14, 2002 10:14 am

inverse curve

Post by dale elsen » Sat Jan 25, 2003 7:47 pm

Any help would be appreciated; just imported some points from another cogo program. As usual, I use MS for inversing to draw the linework,brgs.
distances which come out nicely. Cannot find in the help how to inverse
through the curve;when I enter the bc,rad pt,ec, it wants to draw the routine with baseline dist. and perpo offset dist.,sometimes MS calls a 3-point calculation.
The other curve routines seem to be for creating curves only. Must be an IC (inverse curve) routine somewhere. Thanks folks!!

Glen Cameron
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada

Curve Inverse

Post by Glen Cameron » Sun Jan 26, 2003 7:02 am

What this is telling you is the distance from the beggining of the curve to the radial point is not equal to the distance from the end of the curve to the radial point. Because they are not equal, when you inverse the 3 points we will not handle it as a curve (they have to be equal to be a curve). Instead it is calculated, as you mentioned, as an Angle left and right as well as a Baseline Offset calculation.

There are two ways to correct for this situation.

1) Reset the location of the radial point, being it is not really the radial point, being it is not accurately set. You can do this by using the Distance Distance intersection calculation in COGO.

2) Often the inaccuracy in the location of the radial point is due to rounding errors from other programs. To allow you to still use the point, as it is set, and get a curve we do have a FUDGE FACTOR that you can control.

This fudge factor is actually our Point Protection Tolerance. On the General Configurations Dialog box, the Point Protection Tolerance, controls if the curve inverse will give the curve or the alternate info, as mentioned above.

As an example;

If the first inverse was equal to 107.3033
and the second equal to 107.2933, the radial point is not perfect and if the Point Protection Tolerance is set to 0.001 or smaller, then we get the 3 point inverse which displays the angle left and right as well as the Baseline Offset.

Change the Point Protection so it is equal to 0.01 and now the COGO 3 point inverse will give you the curve information, and draw the curve on screen, if the toggles are set to do so. The Radius used to calculate the curve info is 107.3033, in this example.

Glen W. Cameron, C.E.T.
City of North Bay, Ontario

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