Lines

To Quickly Access Specific Infomation.

• Line Features
• Curving Line Features
• Parallel Line Features
• Offsetting Line Features
• Giving Widths To Lines
• Gapping Line Feature
• ISO Tree Canopies
• Overrides
• Changing Codes
• Comma Codes and Dimensions for Constructions
• Line Formation in Segments

Line Features

Some features, such as building footprints, are often closed polygons where the last point links back to the first.  There are two ways that you can force a line feature to be a polygon.

The Polygon comma code, normally P, can be assigned to either the first or the last point of a feature.  This can be used for “one-off” features that need to be closed, such as the feature strings around the bottom of a series of spoil heaps.

The attribute check button Auto Close allows you to specify that all features using a code prefix are polygons.  This can be used where the feature represents a building footprint or a pedestrian refuge in the middle of a carriageway.

You should note that when displaying the closing segment of a polygonal feature, any curve fitting is carried through from the end of the feature back to the beginning.

Curving Line Features

There is often the requirement to display part or all a line feature as curved segments.  Kerbs in towns and cities are seldom straight.

The Curving comma code, normally C, specifies that the line feature generated using a given point will be curved at that point.  A curve can only be generated if one of the curve comma codes has been applied to both points of a line feature segment.  If the line segment prior to the point is straight, a discontinuity in the curve will exist.  The same applies where the following segment is straight.  If both prior and following segments are curved, there is a common tangent direction at the point.

The Curve Discontinuity comma code, normally D, specifies that if both the prior and following line feature segments are curved, there is no continuity of the curve direction through the point.

Straight Feature	Curved Feature	Curved Feature with Discontinuity

The first of the examples above show the starting point of a feature made up of straight-line segments.  The second shows how curve fitting is applied to all the segments of the feature.  The third shows how a curve discontinuity can be introduced to one of the points.

The Tangent comma code, normally T, specifies that the line feature segment prior to or following the point is a tangent.  If the prior segment is straight, the direction of this segment is used to constrain the start direction of the following segment.  If the prior segment is curved, the direction of the following segment is used to constrain the end direction of the prior segment.  Some examples are shown below.

Single Tangent	Double Tangent	Quadruple Tangent

The first of the examples above shows how a series of curved segments are followed by a straight segment using a tangent point.  The second shows how a single curved segment can be created between two straight line segments by using two tangent points.  The third shows how a 4-point polygon with four tangents can be used to simulate a pedestrian refuge in a road.

Parallel Line Features

It is possible to use dimensions that create lines that are parallel to surveyed lines.  For instance, you could survey one face of a wall and create a parallel line that represents the other.  The parallel offset dimension, normally P=, is used to do this and an initial value must be placed on either the first or last point of the feature.  Note that if the attribute check button P, O&W on First Only is ticked, n4ce will not look for the initial offset on the last point of the feature.  The initial parallel dimension will be used until another parallel dimension has been assigned to a point.  Once this happens, this new offset will be used for the next and subsequent line feature segments until the end of the line feature or until another offset is found.

In its simplest form, there will be two parallel lines drawn using the same line style and pen.  The perpendicular distance between them will be the dimension value.  The first of these lines will be drawn on the surveyed line and the other to the left or right.  If the dimension value is negative, the second line will be to the left of the first.

You can further enhance the parallel line by defining the dimension as a series of up to three comma-separated strings, for example, P=offset, prefix,dz.  The first string is the value of the parallel offset.  The second string is the code prefix that is to be used to display the parallel line.  The third-string is the height offset from the surveyed feature to the parallel feature.  This can be used to create a combination of channel and kerb lines and you should note that this will only work for features where the height offset is assumed to be constant.

You can only define the parallel line prefix using the initial parallel dimension.  If it is defined in subsequent dimensions, it will be ignored and only the parallel offset used.  However, you can also use a dimension, fixed as FPL=, to define the code prefix that is to be used.  This can be defined as a default code prefix field, so it does not have to be entered when surveying.  This could be used to simulate the survey of one hedge face and using a parallel feature to create the other.

If the attribute check button Close Ends on P&W is ticked, the ends of the two lines will be joined by additional segments to create a closed polygon.  If the parallel line is using a different code prefix to the surveyed line, the closing segments will use the line style and pen of the parallel line.  Note that if you are creating a parallel line to a closed feature, the setting of this check button is ignored.

Parallel	Parallel with Code	Parallel with Code (Closed Ends)

The first of the examples above shows a simple parallel where only an offset value is provided in the parallel dimension.  The second shows a parallel with curved segments where an offset and a code prefix are provided in the parallel dimension.  Using these two examples, the offsets from the first point to its calculated parallel show how the parallel calculations are affected by curve fitting.  The third is the same as the second except the code prefix settings have been modified such that option to close the ends of the surveyed and parallel lines are enabled.

The actual calculations of the parallel line can depend on which comma codes and dimensions have been assigned to a point.  The normal parallel method for straight-line segments is to create parallel segments for the two segments before and after each point.  Where these segments would intersect, a point is created.  If there is curve fitting through a point, a tangent to the curve is calculated and a perpendicular offset calculated.  If any point on the base string has a Bearing dimension, BRG, a perpendicular offset is calculated using this dimension.

The examples above show how a parallel line is created where the parallel offset is constant.  However, this parallel offset can be varied along the length of the feature.  How this variable offset is used is defined by the POW Variable check button.  If this check button is not checked, n4ce will use the parallel offsets to ensure that each segment on the parallel feature is mathematically parallel to its parent segment on the surveyed feature.  If this check button is checked, n4ce will vary distance along each parallel segment using the offsets at either end of the feature segment.

Non-Variable Parallel	Variable Parallel	Curve-fitted Variable Parallel

The way in which the parallel offset should be measured is different for each case.  The first example on the left shows a parallel feature where the POW Variable button has not been checked.  The parallel offsets should be measured perpendicular to the line segments and curve-fitting should not be applied to such features as it could produce unpredictable results.  The second example shows a parallel feature where the POW Variable button has been checked.  In this case, the parallel offsets should be measured across the corner rather than perpendicular to the segment direction.

The third example shows how a variable width hedge can be generated using two different line styles together with the FPL= dimension to define a second code prefix.  It also shows that the variable parallel hedges can be curve-fitted to good effect.  If there is a need to display a centre-line between the two parallel lines, you can specify a default field called FCL containing a code prefix to use.  If this is defined, a centre-line will be generated using the line colour and style for that code prefix and is shown in the example above.

Offsetting Line Features

The Offset dimension, normally O=, can be used to offset the line feature to the left or right of the surveyed line. The initial offset can be assigned to either the first or the last points on the feature.  Note that if the attribute check button P, O&W on First Only is ticked, n4ce will not look for the offset on the last point of the feature. The initial offset dimension will be used until another offset dimension has been assigned to a point.  Once this happens, this new offset will be used for the next and subsequent line feature segments until the end of the line feature or until another offset is found.

If a line feature is offset, the surveyed points will be displayed where they were recorded.  It is the display of the line feature that will be offset.   If the dimension is negative, the line will be offset to the left.  You can use this in conjunction with the parallel line dimension to create asymmetrically spaced lines.

Offset Feature	Negative Offset Feature	Offset Feature with Parallel

In the examples above, the first point on the feature is to the left.  The first example shows a feature with a positive offset value.  The second shows a feature with a negative offset value.  The third shows a feature with a negative offset value and a positive parallel value, with code prefix.  The above examples show how an offset line is created with a constant offset from the surveyed positions.

You could consider an offset feature to be a parallel feature where the surveyed feature is not drawn as a line.  Therefore, if the offset varies, the new points are calculated as perpendicularly offset from the surveyed line segments unless the POW Variable check button is checked.  However, the FP= dimension has no effect.

Giving Widths To Lines

The Width dimension in lines, normally W=, can be used to give a survey feature a width and there are two ways the width can be used.

If a feature is width scalable, such as a hedge, the line that is displayed will be scaled up such that the width of the line pattern is the same as the value in the dimension.  The attribute check button Width Scalable is used to signify whether a line feature of this type.  The attribute check button Offset Half Width will also be enabled and this allows you to survey the face of the feature and offset the displayed line by half the width.  For this type of line width, the width dimension can be changed at any point and the new value of the dimension will then be used until it is replaced.  You should note that the width of each line segment does not taper between two points.

If a feature is not width scalable, you can still apply a width dimension.  In this case, two lines will be displayed that are the value of the width dimension apart.  The centre line of these two lines is the surveyed feature.  The initial width should be assigned to either the first or last point on the feature.  Note that if the attribute check button P,O&W on First Only is ticked, n4ce will not look for the width on the last point of the feature. The initial width dimension will be used until another width dimension has been assigned to a point.

Width Scalable Feature	Offset Half-Width Scalable Features	Feature with Width Applied

The first of the examples above is that of a width scalable feature.  The second is the same but with the feature being offset by half of the width.  The third is that of a simple line feature width a width applied thus using the surveyed line as the centre line of two parallel lines.  Note that the option to close the ends of the feature has been applied using the Close Ends on P&W checkbox.  The above examples assume a constant width.

If the width varies along with the feature, the calculations used are once again dependent upon whether the POW Variable check button is checked.  It is not checked, the width will not vary along each segment whilst, if it is, the lines either side will “splay”.  If we take the examples for parallel lines with varying widths and assume that the surveyed line is the centre line between the two constructed lines, the same result would be produced for the same values of width.

If the line is not width-scalable and there is a need to display a centre-line between the two parallel lines, you can specify a default field called FCL containing a code prefix to use.  If this is defined, a centre-line will be generated using the line colour and style for that code prefix.

Gapping Line Feature

The Gap comma code, normally G, allows you to suspend the drawing of a line feature for a given segment and should be assigned to the point that immediately precedes the required gap.  This may happen where there is a gap in a hedge, a fence or a wall.  The example below shows a gapped hedge and you should note that the calculations for curve fitting are carried out through the gap as though the segment was there.

The attribute check button Alternate Segments allows you to produce a line feature that only displays alternate segments.  Examples of this would be a road marking that does not have standard lengths such as the lines of road hatching used for carriageway separation.

ISO Tree Canopies

It is sometimes necessary to survey tree canopies more accurately by recording the spread of the tree in more than one direction.  The International Standards Organisation defines that four spreads should be recorded and these should be at the four main compass points from the centre of the tree bole.  If attribute check button ISO Tree Canopy is checked, it is assumed that this is what has been surveyed.

Each point where a tree canopy is to be produced is assumed to have a Tree Canopy dimension, TC=.  The dimension string is a comma separated string of the four spreads starting at north and proceeding clockwise around the point, thus taking the form TC=N,E,S,W.  The line that is produced at each point is a 4-point curve fitted polygon and there is no line connecting the points along with the feature.

Overrides

The Style dimension, normally LS=, can be used to change the line style that a feature uses.  It should be assigned to the first point of the line feature and is the name of the line style.  This can be used where you are surveying road markings and wish to use one code but select the type of road markings from a list on your survey instrument or logger.

The Colour dimension, normally LC=, can be used to change the colour that a line feature uses.  It should be assigned to the first point of the line feature and is an integer value which maps to the list of colours in the n4ce defaults.

Changing Codes

When surveying linear features, it is often required that the same point is used for more than one feature.  This can happen where a fence changes into a wall or where a gate is in the middle of a fence.

The New Code dimension, normally N=, can be used to change the feature code at the current point.  The point will be used twice, to end the current feature and to start a new one with the code taken from the dimension value.  The point will only be displayed once along with its annotation.

The Seg Code dimension, normally M=, can be used to change the feature code for the line segment that follows the current point.  Just the one segment will use the new code and subsequent segments will revert to using the normal point code.  This dimension only works where the segment code is either another line or a 2-point symbol.

New Code Dimension	Segment Code Dimension	Segment Code Dimension

The first of the examples above shows the use of a new code dimension where a hedge finishes and a fence starts at the same point.  The second shows the use of the segment code dimension where a single segment of the hedge is displayed as a fence.  It also illustrates how the curve fitting is carried through the feature regardless of the change in code.  The third shows the use of the segment code dimension where a single segment of the hedge is displayed as a gate.

It is possible to include either of these dimensions into the point code by identifying separator characters for such items.  These are defined in the Dimension Strings Dialog.  The New Code Separator field defines a character that is used to indicate the presence of a new code dimension.  In the first example above, with the new code separator being a slash, the point code should be HE01/FE01.  The Seg Code Separator field defines a character that is used to indicate the presence of a segment code dimension.  In the second and third examples above, with the segment code separator being a colon, the point codes should be HE01:FE or HE01:GT.

If you do not wish to use the code separators, ensure that these fields are blank.  If you do wish to use them, ensure that the character you have chosen is not alphanumeric and easy access from your total station or data logger keyboard.  You should also ensure that you do not use the same characters like those you have specified to indicate a comma code.  Also, you cannot use both separators on the same code.

Comma Codes and Dimensions for Constructions

There are comma codes specifically related to building surveys that allow you to alter the shape of line features.  An example is to allow the creation of a hidden corner next to a chimney breast or an alcove.  Currently, these comma codes are fixed and cannot be changed.  In each of the examples, the solid line is the line that is displayed and the dashed line shows what would be displayed without the comma code.  The comma code is placed next to the point in the sequence to which it should be added.

The Perpendicular Corner Before comma code, fixed as H, requires a sequence of four survey points with the comma code on the last point.  An extra line vertex will be created where a line through the third point which is perpendicular to the line joining the third and fourth points intersects with the line extrapolated from the first and second points.

The Perpendicular Corner After comma code, fixed as J, again requires a sequence of four survey points with the comma code on the last point.  An extra line vertex will be created where a line passing through the second point which is perpendicular to the line joining the first and second points intersects with the line extrapolated from the third and fourth points.

The Corner Merge comma code, fixed as K, requires a sequence of four survey points with the comma code on the last point.  An extra line vertex will be created where the line extrapolated from the first and second points intersects with the line extrapolated from the third and fourth.

The Corner Before comma code, fixed as L, requires a sequence of three points with the comma code on the last point.  An extra line vertex will be created where a line passing through the second point which is perpendicular to the line through the second and third points intersects with a line passing through the first point which is parallel to the line passing through the second and third points.

The Corner After comma code, fixed as M, also requires a sequence of three points with the comma code on the last point.  An extra line vertex will be created where a line passing through the second point which is perpendicular to the line through the first and second points intersects with a line passing through the third point which is parallel to the line passing through the first and second points.

The Segment Offset comma code, fixed as O, requires a sequence of three points with the comma code on the second point.  With this comma code, two extra line vertexes will be created such that they represent a line passing through the second point which is parallel to the line created by the first and third points.  This can be used to simulate an alcove in a wall.

Perpendicular Corner Before	Perpendicular Corner After	Corner Merge
Corner Before	Corner After	Segment Offset

The Line Extension dimension, fixed as X=, allows you to extend a line segment into a corner that is not visible from the survey instrument.  It should appear on the second of a pair of points where the line between the two points needs to be extended and the value of the dimension will be used to extend the line segment in a plan.

The 3-D Line Extension dimension, fixed as XZ=, is similar to the above dimension.  However, the value of the dimension will be used to together with the heights of the points to extend the line segment in 3-D.

Line Formation in Segments

The Line Formation dimension, fixed as LF=, allows you to create more complex constructs within line segments based upon directions and distances.  Basically, the dimension is a sequence of pairs of numbers with the first giving a direction indicator relative to the last direction and the second defining the distance.  Each of the numbers in the dimensions string should be separated with a comma, a space, a slash or a hash character.

The diagram below shows what the value of the first number, or direction, means.  If the value is -2, the distance will be applied to the left of the current point perpendicular to the current direction.  If the value is -1, the distance will be applied 45º to the left of the current direction, or half-left.  If the value is 0, the distance will be applied in the same direction.  If the value is 1, the value will be applied 45º to the right of the current direction, or half-right.  If the value is 2, the distance will be applied to the right of the current point perpendicular to the current direction.

The diagram below shows various ways that the line formation dimension can be used to construct additional detail in line features.

The first segment, between points 1 and 2, has a squared construct starting 5 along from point 1 in the direction of point2.  Since point 1 is the first point on the feature, the start direction is assumed to be the direction between points 1 and 2.  The dimension assigned to point 1 is LF=5,-2,5,2,5,2,5.  This reads as go along 5m, then go left 5m and then go right 5m twice.  Once the end of the construct is reached, the line will then be joined to the point 2 of the feature.  Note that this dimension has an odd number of values and, therefore, n4ce assumes the first value is a distance in the direction of the segment, effectively changing the dimension to be LF=0,5,-2,5,2,5,2,5.

The second segment, between points 2 and 3, has an octagonal construct appended to its end.  In this case, the dimension contains an odd number of values and, therefore, the first value is assumed to be a distance along and the start direction is the direction of the segment from 2 to 3.  The dimension assigned to point 3 to create this is LF=1,2,1.25,-1,2.5,-1,2.5,-1,2.5,-1,1.25.  This reads as go along 1m then go right 1.25m.  After this, go half-left 2.5m 3 times and finally go half left 1.25m.   Once the last point has been constructed, it is then joined to point 4.

The third segment, between points 3 and 4, has another squared construct appended to the end of it.  In this case the dimension contains an even number of values and so the initial direction is assumed to be the direction of the previous segment.  The dimension assigned to point 4 is LF=-2,5,2,5,2,5.  This read as go left 5m and then go right 5m twice.   Once the last point has been constructed, it is then joined to point 5.

There is no dimension assigned to point 5 but the construct after point 6 shows that line formations can be used to extend the end of line features.  In this case, the start direction is the direction of the segment between points 5 and 6.  The dimension assigned to point 6 is LF=-2,5,-2,5,2,5,-1,5.  If you wish to extend the segment 5 to 6, you should insert the value of the extension as the first value in the dimension string.

If you are generating a construct from the last point of a closed feature, the final point of the construct is joined to the first point of the feature.