Circle

This function allows you to create a closed segment which is an approximation of a circle. The closed segment consists of a number of short line segments with a specified distance between points on the circle circumference.

To run this function: Choose Create > Circle by selection , or...

• In the Function Chooser, type CIRCLE, and press ENTER.

Select the point of interest

Position the pointer and select the point which is to be the used as the centre of the circle.

The Circle function will continue until the Cancel button is pressed.

Selection of the point will display the ENTER PARAMETERS FOR A CIRCLE form. Enter the circle creation parameters.

Radius

Enter the radius for the circle.

Arc distance

Enter the arc distance required between the points on the circumference to create the circle.

Define parameters for the plane of the circle

The circle which is created may be defined to be in a plane of any orientation and inclination. This is done by defining the bearing and dip of the plane in which the circle is required.

Bearing

Enter the bearing of the plane which is to contain the circle. The value entered MUST be a DECIMAL angle regardless of the unit of angle measure (degrees or grads).

Dip

Enter the dip of the plane which is to contain the circle. The value entered MUST be a DECIMAL angle regardless of the unit of angle measure (degrees or grads).

Note:Values of 0 for both will create a circle in the horizontal plane.

A segment containing points at the specified intervals is created. The Z value of the points on the circle segment is determined by using the Z value of the centre point, the radius, and design gradient.

The screen is updated to reflect the changes made.

Add	The new segment is added into the design string in the active layer.
Change	Does not apply.
Insert	Does not apply.

Circle by drag

This function allows you to create a closed segment which is an approximation of a circle. The closed segment consists of a number of short line segments with a specified distance between points on the circle circumference. The circle is defined using a click and drag action to define the circle centre point at the location of the first mouse button press. The circle radius is defined by the distance between the location where mouse button was pressed and the location where the mouse button was released.

To run this function: Choose Create > Circle by drag , or...

• In the Function Chooser, type CIRCLE BY DRAG, and press ENTER.

Click and drag to define the circle centre and radius

Position the pointer and use a click and drag action to define the circle centre and radius.

The Circle Drag function will continue until the Cancel button is pressed. Note that the click and drag action is sensitive to snap mode. Thus it is possible to digitise the circle centre at the mouse location or to snap to a specific point.

Releasing the mouse button after the click and drag action to define the circle will display the Enter Parameters For A Circle form.

Radius

Enter the radius for the circle. The default value displayed is that defined by the click and drag action using the mouse.

Arc distance

Enter the arc distance required between the points on the circumference to create the circle. The arc distance defaults to 1/30th of the circle circumference.

Z

The Z value of the circle is initially obtained from the position defined by the mouse. It will either be the Z value of the point to which the centre point is snapped, if using snap mode, or the Z value of the closest piece of geometry otherwise. This Z value may be modified to ensure the circle is at the correct elevation.

The segment representing the circle is always added to the design string number.

Curve Tangent

This function allows you to create a curve which is controlled by defining two lines which are tangents to the curve and by specifying the curve radius, optional transition length and the arc length between points.

To run this function: Choose Create > Curve from tangents, or Design > Road design > Curve from tangents, or...

• In the Function Chooser, type CURVE TANGENT, and press ENTER.

When using 2 tangents, provided they are not parallel lines, a radius and an optional transition to define a curve there are 2 possible solutions. These two solutions are:

• The internal curve that passes through less than 180 degrees
• The external curve that passes through greater than 180 degrees.

This function permits you to create either of these curves at your discretion.

Select the first point on the first line

Position the pointer and select a point on the first tangent to the curve. The point is not necessarily where the tangent meets the curve. Select the first point on the first tangent to display the prompt:

Select the second point on the first line

Position the pointer and select a second point on the first tangent to the curve. The point is not necessarily where the tangent meets the curve. Select the second point on the first tangent to display the prompt:

Select the first point on the second line

Position the pointer and select a point on the second tangent to the curve. The point is not necessarily where the tangent meets the curve. Select the first point on the second tangent to display the prompt:

Select the second point on the second line

Position the pointer and select a second point on the second tangent to the curve. The point is not necessarily where the tangent meets the curve. Select the second point on the second tangent to display the PARAMETERS FOR A CURVE BETWEEN TANGENTS form.

Order of Point Selection

The order in which the points are selected to define the tangents to the curve has an impact on the resultant curve that is created. The two line segments defined by the 2 pairs of points will intersect at a point. This point is commonly referred to as the intersection point, especially for road design applications.

By changing the order in which you select the four points that define the two tangents for this function you can have 4 different possible curves created. Eight if you consider internal and external curves. To help you understand which order you should select the points to achieve the desired result, use the following steps:

• Imagine yourself standing at the intersection point
• The direction defined from point 1 to point 2, in that order, should point towards the intersection point
• The direction from point 3 to point 4, in that order, should point away from the intersection point
• By selecting the points in this order, the curve will be created such that the first tangent is to the right and the second tangent is to the left when viewed from the intersection point.

Radius

Enter the radius for the circle.

Arc distance

Enter the arc distance required between the points on the circumference to create the circle.

Curve type

When using 2 tangents, provided they are not parallel lines, and a radius to define a curve there are 2 possible solutions. These two solutions are:

• The internal curve that passes through less than 180 degrees
• The external curve that passes through greater than 180 degrees.

Choose internal or external to create the curve that you require.

Use transition curve

Tick Use transition curve to allow a transition curve to be added to the curve. When a transition curve is used, a marker will be created in the D3 field (see the road design DField quick reference for more details on the DFields used in road design) of the new curve at the point where the transition curve meets the circular curve.

Transition Length

Enter the length of the desired transition in this field.

Velocity / Calculate

The Calculate button will use the velocity and curve radius to generate a recommended transition length.

The Curve Tangent function will continue until the Cancel button is pressed.

Result

A segment containing points at the specified intervals is created. The Z value of the points on the curve are determined using the following logic:

• The Z value of the first curve tangent point is determined by interpolating along the line between the first and second points which where selected, and
• The Z values around the curve are determined by using the Z value of the tangent point and the design gradient and arc distance from the tangent point.

Internal curve

External curve

The picture is updated to reflect the changes made. The new points are created in a string segment as determined by the Point Mode. The table below shows the different possibilities for this function.

Add	The new segment is added into the design string in the active layer. If the first point selected is not in the active layer then the result will always be as if MODE Add is in effect.
Change	Does not apply.
Insert	The new points are inserted after the first selected point into the segment containing the first selected point.

Warnings

The two points selected are the same. This is not permitted. Please reselect the points.

The two points that have been selected to define a tangent to the curve are the same. You must select two different points to define a line.

Lines are parallel - no intersection possible

The 2 tangents that have been defined are parallel lines. It is not possible to unambiguously fit a circular arc between parallel lines. You must reselect the tangents.

Can't fit a curve to a straight line. Please reselect the tangent points.

The to tangents are colinear, that is, all 4 points fall on the same line. A curve cannot be fitted to these lines. You must reselect the tangents.

Warning: Validation of field transition_length failed

This warning indicates that the desired transition length cannot be used with the current radius. This is more likely to occur when the transition length is greater than the radius.

Curve End

This function allows you to create a curve by selecting two points which define the orientation of a tangent to the curve and the tangent point of the curve and the radius, arc length, length and optional entry and exit transition lengths of the curve.

To run this function: Choose Create > Curve at segment end, or Design > Road design > Curve at segment end, or...

• In the Function Chooser, type CURVE END, and press ENTER.

Select first tangent point

Position the pointer and select the point which will define one end of the tangent line to the curve.

At the prompt:

Select second tangent point

Position the pointer and select the point which will define both the other end of the tangent line and also the tangent point where the curve meets the defined line tangentially.

The CurveEnd function will continue until the Cancel button is pressed.

Selection of the tangent points will display the PARAMETERS FOR A CURVE AT END OF LINE form. Enter the remaining curve parameters.

(C)lockwise or (A)nticlockwise

Respond with:

• A, to make the curve anticlockwise, or
• C, to make the curve clockwise.

Radius

Enter the radius for the circle.

Curve (A)ngle or (L)ength

This input indicates how to specify the length of the curve.

Respond with:

• A, angle, or
• L, length.

Angle or Length

If you selected a length enter the distance. If you selected an angle, enter the angle in the format described below:

• If you have selected DEGREES as your Angle units, the angle must be entered in DDD.MMSS format.
• If you have selected GRADS as your Angle units, the angle must be entered in GRADS to four decimal places.

If either an entry or exit transition curve is used, the values entered for the angle or length are inclusive of the angle turned by the transition curves or their lengths respectively.

Arc distance

Enter the arc distance required between the points of the string which makes the circle.

Use entry transition curve

Tick Use entry transition curve to allow a transition curve to be added to the beginning curve. When a transition curve is used, a marker will be created in the d1 field of the new curve at the point when the transition curve meets the circular curve.

Entry transition length

Enter the length of the entry transition in this field.

Use exit transition curve

Tick Use exit transition curve to allow a transition curve to be added to the end curve. When a transition curve is used, a marker will be created in the D3 field of the new curve at the point when the transition curve meets the circular curve.

Exit transition length

Enter the length of the exit transition in this field.

Velocity / Calculate

The calculate button will use the velocity and curve radius to generate a recommended transition length for either of the requested entry or exit transitions.

A segment containing points at the specified intervals is created. The Z value of the points on the curve are determined using the following logic:

• the Z values around the curve are determined by using the Z value of the tangent point and the design gradient and arc distance from the tangent point.

The picture is updated to reflect the changes made.

Add	The new segment is added into the design string in the active layer. If the first point selected is not in the active layer then the result will always be as if MODE Add is in effect.
Change	Does not apply.
Insert	The new points are inserted after the second selected point into the segment containing the second selected point.

Warnings

The first and second points selected are the same. This is not permitted please reselect the points.

Two different points on the same segment must be selected.

Drive Outline

This function allows you to create a closed roadway outline by selecting a portion of a segment to be a centre line and entering offset distances to the left and right.

To run this function: Choose Create > Road from centreline, or Design > Underground tools > Road from centreline, or...

• In the Function Chooser, type DRIVE OUTLINE, and press ENTER.

Select centre line start point

Position the pointer and select the point which will be the start point of the centre line.

At the prompt:

Select centre line end point

Position the pointer and select the point which will be the end point of the centre line.

The Drive Outline function will continue until the Cancel button is pressed.

Selection of the centre line start and end points will display the CREATE A DRIVE STRING FROM A CENTRE LINE form. Enter the offset distances.

Offset left

Enter the offset distance to the left of the centre line as a positive number.

Offset right

Enter the offset distance to the right of the centre line as a positive number.

A closed segment which represents a roadway outline is created. The Z value of the points on the outline segment are the same as the Z values of the points on the centre line segment from which they were created.

The screen is updated to reflect the changes made.

Add	The new segment is added into the design string in the active layer. If the first point selected above is not in the active layer then the result will always be as if MODE Add is in effect.
Change	The new segment has the same string number as the centre line string.
Insert	The new segment has the same string number as the centre line string

The start and end points selected are not on the same segment. 
		Please try again.

Grade segment

This function allows you to alter the gradient along a segment between selected points.

To run this function: Choose Edit > Segment > Change gradient , or...

• In the Function Chooser, type GRADE SEGMENT, and press ENTER.

Select centre line start point

Position the pointer and select the point at the start of that part of the segment which is to have its gradient changed to display the prompt:

Select centre line end point

Position the pointer and select the point at the end of that part of the segment which is to have its gradient changed to display the GRADE A SEGMENT form.

Note: The points may be selected in any order i.e. ascending or descending, along the segment and a meaningful result will still ensue.

Gradient

Enter the new gradient for the selected segment. The value is assumed to be expressed in the units from the field above. The value may be positive or negative. Negative values represent a downhill gradient, while positive values represent an uphill gradient. The average gradient is displayed as the default value.

Note: The following values are not allowed: ratio of 1 in 0 or an angle of 90 degrees or 100 grads. Conversion from a gradient of 0%, degrees or grads to a finite ratio is not possible.

Units

Enter the units for the new gradient. The default value for this field is taken from the grade units specifier found in the defaults.ssi file.

The units must be one of:

• ratio, for a gradient of the form `1 in X'
• angle, for a gradient of the form `X degrees' or `X grads'
• percentage, for a gradient of the form `X%'

Approximate circular arcs

Portions of segments sometimes represent circular arcs. This typically occurs after using the CIRCLE, CURVE TANGENT or CURVE END functions. The GRADE SEGMENT function can consider such approximations as circular arcs if necessary when calculating the elevations using the new gradient or, the segment can be considered as a simple collection of straight line segments.

By approximating circular arcs the effect is to use a longer distance as the arc distance around such curve approximations is always greater than the comparable chord distance. This in turn results in a greater difference in elevation when using the arc distance than the chord distance. The total difference in elevation between the 2 methods is relatively insignificant on short segments but for long segments it may be quite substantial.

Enter Y to use arc distances for circular arc approximations that may be present in the segment. Enter N to use the chord distance.

Circular arcs are determined by scanning the segment and any group of 4 or more consecutive points that fall on the same circular arc are subsequently used in the calculation of arc distances using the derived radius of curvature.

The Grade Segment function will continue until the ESC key or any other key is pressed when the point selection prompt is displayed.

Result

The Z values of the points on the segment from the first selected point up to and including the second selected point are altered so that the specified gradient applies between the two points.

The screen is updated to reflect the new gradient on the selected portion of the segment.

Warnings

The start and end points selected are not on the same segment. Please try again

The selected points must be part of the same segment.

The point selected is not in the working layer and cannot be edited.

The point selected is not in the active layer. It is not permissible to change data that is not in the active layer.