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
Let’s study tracing polylines using Image_3
of the Trace.cws file from the Lesson_7
folder.
Choose Open
from the File menu. Open the Trace.cws file from the
Lesson_7
folder.
Before tracing you need to tune the tracing parameters.
Choose Conversion Options from
the Convert
menu.
In Options tab:
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Define Max.Width
using the Measure button - measure the width of the thickest traced polyline.
Specify this parameter value slightly greater than the measured
width.
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 |
| (e.g., if the measurement result is equal to 0.59 - specify 0.8
in the Max.Width
field). |
Set the Accuracy
slider to High, if you want the vector polyline
to be extremely close to the shape of the raster curve.
In Separate tab:
INFORMATION:
You can place objects created through tracing, to a predefined layer.
To define a new layer, open Layer Manager (by choosing Layers
from the Tools menu), press the New
 button.
Press the Details button in the Name
field, and then specify a name for the created 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 width
in the Width field.
Select the Use Table checkbox.
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In Trace tab:
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To estimate the tracing direction automatically, select the
Auto Detect Direction
checkbox in the Trace tab, and a pause 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 the 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).
If you are not happy with the direction suggested by the program,
specify the correct direction on the screen.
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If you want to change the tracing direction choose Change direction from
the right-button menu.
To cancel the last segment of the vector polyline, press Ctrl+Backspace.
To cancel the last step, press Backspace.
If needed, you can draw segments in Free Hand Drawing mode. Press Shift
and specify the new nodes of the vector polyline on the screen.
When you have finished tracing the polyline, press Enter.
TIPS:
You can use the Centralize
View command from the context menu for convenience.
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 section Tuning tracing for information on tuning the other tracing
parameters.
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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- Line Following.
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Specify points on the raster objects, which you want to approximate
by vector polylines with orthogonal segments.
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Tracing raster outlines
Let’s study tracing
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.
Method 1 - tracing by boundary
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Open the Trace tab of the R2V
Conversion Options dialog.
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As we intend to trace contours with orthogonal segments, select
the Line
Follow Orthogonalization and Auto estimate base angle checkboxes.
Select the Export single contour checkbox - the program will ignore
the contents of the closed contour.
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See section Tuning tracing for information on tuning the other tracing parameters.
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Open the Inspector by choosing Inspector from the Tools
menu. From the list in the Hatch Type field, choose Solid
Fill; in the Color field choose a color.
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Open the Raster To Vector toolbar.
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Choose the tracing parameters - for example, Make Vector and
Keep Raster by pressing the Make Vector and Keep Raster button, and
then the tracing command - Trace Outline.
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Specify points inside the raster contours.
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Method 2 - tracing by contour
line
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Open the Trace tab of the R2V
Conversion Options dialog.
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As we intend to trace contours with orthogonal segments, select
the Line
Follow Orthogonalization and Auto estimate base angle checkboxes.
Select the Auto Extend Vectors checkbox - the program will consider the
width of the raster line limiting the contour.
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Select the Export single contour checkbox - the program will ignore
the contour contents.
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Open the Raster To Vector toolbar.
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Choose a tracing mode - for example, Make Vector and Erase Raster by pressing the Make
Vector and Erase Raster button (in this case, the program
deletes the contour contents), and the tracing command - Trace Outline.
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| If you choose Make Vector and Keep Raster mode the program will keep the outline
contents. |
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Specify points inside raster contours.
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