This week’s blog post is curves in Civil 3D fieldbooks. Most curves can be put into a fieldbook. However, there are times when a plat may not contain enough information and you may have to resort to manually drafting one or more curves. Most legals contain more curve information than a plat. When I work with assessor offices, many plats do not include a chord direction with a brokenback curve. Without chord definitions for these types of curves, the fieldbook gives a user few alternative creation methods.
There may be no alternative except to draft in an arc. One can use Civil 3D’s curve and compound/reverse curve drafting commands. After creating the curves, the curves may need to be moved and/or rotated into position. When rotating, and trying to correctly locate a curve, I find rotate’s reference option most useful. I select the arc, set the pivot point and reference the chord from the pivot point to the curve’s end point. The curve then rotates along the curve’s chord and then I select the curve’s rotated end point.
Drafting a legal description’s arc with AutoCAD drafting tools is NOT a sin. Most likely, that is how most brokenback arcs are created.
Figure Curve Commands
There are three basic figure curve commands; tangent, with chord, and refencing points (tangent and broken back).
Tangent Curve
By far, a tangent curve is the easiest curve creation method. The command is like the curve from the Ribbon’s end point command. Sadly, this command MUST have a preceding tangent segment. Consequently, the fieldbook MUST define a tangent segment BEFORE this curve command.
The following is the documentation for the CRV command.
CRV [DELTA, LENGTH, DEFL, MID, TAN, CHORD] [radius] [value]
The additional piece of curve information is one of the following:
DELTA The value supplied is the curve’s include angle
LENGTH The value supplied is the curve’s length
DEFL The value supplied is the curve’s deflection angle (variation from the preceding tangent’s direction)
MID The value supplied is the curve’s mid-ordinate value
TAN The value supplied is the curve’s tangent length
CHORD The value supplied is the curve’s chord length
The command is written by starting with CRV followed by what addition piece of information is used to define the resulting curve. After specifying the known value type, the radius and the know type’s value is entered. A positive radius value is a right turning and a negative radius value is a left turning curve.
CRV LENGTH 89.50 122.50 A curve with a known length - right turning
CRV LENGTH -75.00 85.75 A curve with a known length – left turning
This curve command also creates compound or reverse curves. In the above code example, the first curve is right turning and the second is tangent at the first’s curve’s end point, but reverses by being a left turning curve (negative radius).
The following is a fieldbook with tangent curves.
BEG INTERIOR DEER MEADOWS
FIG NE 5000 5000
FIG BD 57.2825 1 165.66
CRV LENGTH -107.76 94.41
FIG BD 7.1636 1 186.03
FIG BD 7.1636 1 250.00
FIG BD 7.1636 1 250.00
FIG BD 7.1636 1 266.87
CRV LENGTH 97.58 119.82
CRV LENGTH 97.58 119.82
FIG BD 32.0027 2 225.00
FIG BD 32.0027 2 300.00
FIG BD 32.0027 2 116.73
CRV LENGTH 120.12 95.32
CRV LENGTH 120.12 69.39
FIG BD 46.3329 3 160.33
FIG BD 46.3329 3 250.00
FIG BD 46.3329 3 250.00
The fieldbook if used with last week’s survey plat fieldbook creates exterior and interior linework. This blog's fieldbook does not close, but creates the interior parcel lines. A couple of the above curves are split between two lots, but you can think of them as an example of compound curves. If the above fieldbook is added to last week’s fieldbook the following figures would show the interior and exterior boundaries for Dear Meadows.
Figure 1: Deer Meadows Exterior and Interior Linework Fieldbooks
Non-Tangent Curves – Chord Based
If the legal or plat has chord bearings for non-tangent curves, you can use the next set of curve commands. A legal may contain a chord bearing and distance, but a plat may not. Again, when I work with assessor offices, this is a topic that comes up regularly, should an assessor’s office require a chord bearing and distance for plat curve’s?
If there is no chord bearing and distance values for a non-tangent curve, it is not possible to draw the arc with these fieldbook commands. A user may have to draft the curve in after creating the linework.
These figure curve commands can create a curve greater than 180˚. The reserved word BULB means that a curve is greater than 180˚. That is why BULB is optional. Even though, the commands are for broken back curves, the command will create tangent curve using the chord values.
The non-tangent-chord based command are:
XC ZD (BULB) [radius] [chord-az] [chord-dis]
XC BD (BULB) [radius] [chord-brg] [quad] [chord-dis]
XC AD (BULB) [radius] [chord-angle] [chord-dis]
XC DD (BULB) [radius] [chord-defl] [chord-dis]
The Legal
THENCE ALONG SAID TOWER LEASE, S 50° 38' 48" W FOR A DISTANCE OF 10.00 FEET TO THE POINT OF BEGINNING OF THE CENTERLINE OF A 20-FOOT-WIDE ACCESS/UTILITY EASEMENT, LYING 10 FEET ON EITHER SIDE OF THE FOLLOWING DESCRIPTION;
THENCE, N 39° 21' 12" W FOR A DISTANCE OF 24.02 FEET TO THE BEGINNING OF A CURVE;
SAID CURVE TURNING TO THE LEFT THROUGH AN ANGLE OF 67° 06' 10", HAVING A RADIUS OF 10.00 FEET, AND WHOSE LONG CHORD BEARS N 72° 54' 16" W FOR A DISTANCE OF 11.05 FEET TO A POINT;
THENCE, S 73° 32' 39" W FOR A DISTANCE OF 53.02 FEET TO THE BEGINNING OF A CURVE;
SAID CURVE TURNING TO THE RIGHT THROUGH AN ANGLE OF 77° 16' 50", HAVING A RADIUS OF 315.00 FEET, AND WHOSE LONG CHORD BEARS S 22° 11' 04" W FOR A DISTANCE OF 393.39 FEET TO A POINT;
THENCE, S 60° 49' 29" W FOR A DISTANCE OF 931.33 FEET TO THE BEGINNING OF A CURVE;
SAID CURVE TURNING TO THE RIGHT THROUGH AN ANGLE OF 16° 15' 46", HAVING A RADIUS OF 1750.00 FEET, AND WHOSE LONG CHORD BEARS S 68° 57' 22" W FOR A DISTANCE OF 495.05 FEET TO THE BEGINNING OF A CURVE;
SAID CURVE TURNING TO THE RIGHT THROUGH AN ANGLE OF 56° 45' 39", HAVING A RADIUS tHE A FEET, AND WHOSE LONG CHORD BEARS N 74° 31' 56" W FOR A DISTANCE OF 451.56 FEET TO A POINT;
THENCE, N 46° 09' 06" W FOR A DISTANCE OF 207.42 FEET TO THE BEGINNING OF A CURVE;
SAID CURVE TURNING TO THE LEFT THROUGH AN ANGLE OF 104° 11' 34", HAVING A RADIUS OF 75.00 FEET, AND WHOSE LONG CHORD BEARS S 81° 45' 07" W FOR A DISTANCE OF 118.36 FEET TO A POINT;
THENCE, S 29° 39' 20" W FOR A DISTANCE OF 89.24 FEET TO A POINT ON THE NORTHERN PUBLIC RIGHT OF WAY OF HARRISBURG AVENUE, SAID POINT ALSO BEING THE POINT OF TERMINUS, CONTAINING 56907 SQFT -AND- 1.306 ACRES.
The above legal snippet would create the following fieldbook:
BEG LOT
FIG NE 5000 5000
FIG BD 39.2112 4 24.02
XC BD -10.00 72.5416 4 11.05
FIG BD 73.3239 3 53.02
XC BD 315.00 22.1104 3 393.39
FIG BD 60.4929 3 931.33
XC BD 1750.00 68.5722 3 495.05
XC BD 475.00 74.3156 4 451.56
FIG BD 46.0906 4 207.42
XC BD -75.00 81.4507 3 118.36
FG BD 29.3920 3 89.24
To be sure, the above fieldbook can be done by using the Ribbon’s Line and Curve commands. Figure 2 shows the result of importing the above fieldbook.
Figure 2: Chord Curve Fieldbook
Curves by Points
The last method creates curves by referencing points. If there are points in a survey and/or drawing, the Line and Curve or Transparent commands are viable tools. But, a fieldbook can also reference points. The only catch is the points must be in the survey that the fieldbook is imported to. How do you get points that exist in a drawing into a survey?
Survey’s Import Even Wizard allows a user to bring points from a drawing to a survey. The points that become a part of the survey are control points and can be referenced by any figure command.
By starting an import event, a user can import points from a drawing. See Figure 3.
Figure 3: Assigning a Drawing as an Import Even Source
After assigning a named network to the imported points, in the Import Option dialog box, set the Point Type to Control point. See Figure 4.
Figure 4: Import the Points as Control points
After selecting Finish, the survey network needs to be updated. The survey now contains control point imported from the drawing. See Figure 5.
Figure 5: The Survey after Import Points from Drawing
Existing Points
When wanting to use survey points in a fieldbook, you do not station on them. Because you are using commands from the Figure command section. In that section to use an existing survey point in a figure, the command POINT is used. The command is:
POINT [point]
The command to create a three-point curve is:
XC C3 [pt on curve] [endpt]
The command assumes that the current position is first of three points or the PC of the curve. The curve is potentially a broken back curve and it uses the XC figure command group. The command remainder is the is the second and the end (third) point on the curve. In the survey with points 1 to 3, the fieldbook would look like the following:
BEG CURVE
POINT 1
XC C3 2 3
Figure 6 is the result of importing point 1-3 and importing the above fieldbook.
Figure 6: Broken-back Curve by Three Points
A second command creates a curve, but one point represents the curve’s radius point. The current point is the curve’s PC and a third point is the curve’s end or PT. The command applies to tangent and broken back curves. The command is:
XC PTS [radius] [radpt] [endpt]
Again, the fieldbook places the figure at a PC point with the POINT command. A fieldbook using this method would be:
BEG CURVE
POINT 1
XC PTS 17.5 2 3
Figure 7 shows the result of having a survey with existing points and importing the above fieldbook.
Figure 7: Arc by Radius Point
Curves in fieldbooks are not always possible. The document you are trying to place in a drawing may not have the information required by the figure commands. When there is not enough information to use the figure curve commands, a user may have to resort to Civil 3D’s line/curve or transparent commands. Most likely Civil 3D users draft lines and curves before thinking of using a fieldbook.
The figure curve commands apply to tangent and broken back curves and can use chords, points, and properties of the curve to draw them as survey figures.
These commands are powerful when legals or plats are complex and lengthy. A fieldbook file allows a user to review the entered data before importing the file. An opportunity to check for errors before creating the figures.
