Lesson 7-2. Tracing raster polylines and outlines
Brief
description: During
this lesson you will learn how to trace raster polylines and outlines.
 For detailed information on these subject see chapters Tuning tracing, Tracing Modes and Commands, How
to trace, Tracing
Polylines, Tracing Outlines in the Tracing section of the Quick Start guide.
Tracing polylines
Create a new AutoCAD drawing.
Using the Open
command from the rFile menu, load the Trace_2.tif document from the Lesson_7
folder.
Before tracing you need to tune the tracing parameters. Choose Conversion Options from
the rConvert
menu.
In Options tab:
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Define the Max.Width setting. Using the Measure
button, measure the width of the thickest polyline. Set
the value of this parameter slightly greater than the measured width
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the Max.Width field). |
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Set the Accuracy
slider to the High position. With this set to high,
the vector polyline will match the raster curve as close as possible.
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In Separate tab:
INFORMATION: You can place objects obtained as a
result of tracing on a pre-defined layer (using AutoCAD tools).
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Create a new AutoCAD layer - Polylines,
for example.
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From the list of the Layers field choose Polylines.
You can also specify a color for vector objects in the Color field and a width
in the Width field.
Select the Use Table checkbox.
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To estimate the tracing direction automatically, select the Auto Detect Direction
checkbox in the Trace tab, and a waiting time in the Pause field.
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Open the Raster To Vector toolbar.
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Choose a tracing mode - for example, Make Vector and Keep Raster
by pressing the Make Vector and Keep Raster
button, and a tracing command - Line Following.
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Specify a point on the raster curve- the program tracks this curve
up to the nearest intersection with another raster line, and then
indicates by a cross the most probable tracing direction.
If you are happy with the offered direction, press the Space key (alternatively, the program will continue tracing
after the pause expires).
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If you are not happy with the direction suggested by the program,
specify the right direction on the screen.
To change the tracing direction, cancel the last step or segment,
draw a freehand polyline segment or pan to the center - use the
right-button menu or the AutoCAD command line.
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Tracing polylines with orthogonal segments
If you want to obtain a polyline with orthogonal segments:
Open the Trace tab of the R2V Conversion Options
dialog.
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Select the Line Follow Orthogonalization and Auto estimate base angle
checkboxes.
See sectionTracing
polylines for information on tuning the other tracing
parameters.
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Open the Raster To Vector toolbar.
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Choose the tracing mode - for example, Make Vector and Keep Raster
by pressing the Make
Vector
and Keep Raster button, and the tracing command- Line Following.
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Specify points on the raster objects, which you want to convert
to vector polylines with orthogonal segments.
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Tracing raster outlines
Let's study how we trace raster outlines, using Image 3 of
the Trace.cws file from the Lesson_7 folder.
Before tracing outlines you need to tune the tracing
parameters. Choose Conversion Options
from the Convert menu.
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Open the Trace tab of the R2V Conversion Options
dialog.
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As we are going to trace contours with orthogonal segments, select
the Line
Follow Orthogonalization and Auto estimate base angle checkboxes.
As we are going to trace contours with orthogonal segments, select
the Line
Follow Orthogonalization and Auto estimate base angle checkboxes.
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Select the Auto Extend Vectors checkbox - the program will consider
the width of the raster line that limits the contour.
Select the Export single contour checkbox - the program will ignore
the contents of the closed contour.
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Open the Options tab of the R2V Conversion Options
dialog.
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Set the Max Break value equal to 0 mm to prevent incorrect definition
of the contour border in the cases if objects inside the contour
are located closely to its border.
Set the Approximation Accuracy slider closer to the Low position to prevent the program
from creating segments by mistake due to the variable line width.
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Open the Raster To Vector toolbar.
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Choose a tracing mode - for example, Make Vector
and Keep Raster by pressing the Make
Vector and Keep Raster button, and the tracing command -
Trace Outline.
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Click one by one the points inside the raster contours, as shown.
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