Tracing

Brief description: Tracing is an interactive (or semi-automatic) vectorization procedure. During the tracing procedure raster objects, specified one by one are recognized and converted to corresponding vector objects. During tracing the original raster objects can be deleted, smoothed or left intact.

Tuning tracing

You should tune the tracing parameters before applying this procedure.
Tracing parameters are tuned in the R2V Conversion Options dialog.
Choose Conversion Options from the rConvert menu.

Tuning geometry of traced objects:

Open the Options tab of the R2V Conversion Options dialog.

Max.Width - the maximum width of traced raster objects. Measure the width of the widest traced lines. Set this parameter value slightly greater then the measured width.

Max. Break - the maximum length of ignored breaks in raster lines.
If you trace dashed lines, set the value of this parameter slightly greater than the maximum gap between the dashes.

Accuracy - When tracing polylines, set this value to high (for more precise approximation of raster curves with vector polylines). In other cases generally  the accuracy value should be increased for images of good quality; and reduced for images of poor quality.

Layering resulting vector objects

You can place vector objects obtained from vectorization onto different layers:

Open the Separate tab of the R2V Conversion Options dialog. From the pull-down list of Layer select one to place the traced vector object. Select the Use Table checkbox.

Tracing in Orthogonal mode

When tracing lines and polylines, you can use orthogonal mode, which allows you to obtain orthogonal lines or polylines that consist of orthogonal segments (the base angle can be calculated automatically or specified).

Tracing lines with orthogonalization

IMPORTANT: This operation can only work if the raster line you want to trace deviates from the orthogonal (specified) direction by no more than 2°.

To turn on the orthogonal mode:

• Open the Options tab of the R2V Conversion Options dialog.
  Select the Orthogonalization checkbox.
• Enter the base angle value in the Base Angle field.

Tracing with resulting polyline of orthogonal segments

This information is provided in section Tracing polylines with orthogonal segments.

Tracing modes and commands

Before executing tracing, you should choose a tracing mode.

Tracing modes:

	Original fragment
	Produce vector and keep raster
	Produce vector and erase raster
	Erase raster without producing vector
	Smooth raster without producing vector

Tracing commands

You can trace:

	Lines, arcs, circles with auto recognition		Hatches which consists of lines
	Lines by two points		Raster symbols
	Arcs by three points		Polylines
	Circles by two points		Outlines

How to trace

• Set the tracing parameters
  Information on setting tracing parameters is provided in section Tuning tracing.
• Choose from the Raster to vector toolbar or from the Trace menu:
  • Tracing mode
  • Tracing command
    More detailed information is provided in section Tracing Modes and Commands.

Tracing lines, arcs, circles, and outlines

	You can trace raster lines, arcs, circles, and outlines with automatic recognition of their type - click once on the desired object.
	If you work with a complicated image, or an image of poor quality, or you need to vectorize only part of a raster entity, you can apply forced tracing.

Auto extension mode:
When tracing lines or arcs you can use Auto extension mode  - you only specify a fragment of the object, but the program recognizes the whole object. To switch to this mode, select the Auto extend vectors checkbox in the Trace tab of the R2V Conversion Options dialog.

Tracing Hatches

To trace a hatch, you need to intersect all its lines with a crossing polyline.
TIPS: raster lines that cross the hatch interfere in the recognition operation, so before tracing the hatch it may be useful to trace these lines and erase the original raster.

Original hatch	Tracing lines that intersect hatch (with erasing the original raster)
Tracing hatch - intersecting hatch lines	Result of hatch tracing (in Produce Vector and Erase Raster mode)

Tracing Polylines

Tracing polylines command produces vector polylines which approximate raster curves. To increase accuracy of approximating vector polyline to the original raster curve increase the Accuracy slider in the Options tab of the R2V Conversion Options dialog. See section Tuning geometry of traced objects for information on tuning tracing.

How to trace polylines:

• Select a tracing mode (e.g., Produce Vector and Keep Raster).
  See section Tracing Modes and Commands for more detailed information.
  
• Press the Trace Polyline button.
• Pick a point on the raster curve - the program tracks this curve up to the nearest intersection and waits for you to indicate the direction in which tracing should continue.
  You can also use the Autodetect direction mode:
  Open the Trace tab of the R2VConversion Options dialog.
  Select the Autodetect direction checkbox.
  Set the waiting period (in sec) in the Pause field.
• If you turn on the Autodetection direction mode, and you are satisfied with the direction indicated by a cross, press the Space key (alternatively, the program continues tracing after the waiting period expires).
  If you are not satisfied with the direction suggested by the program, specify the right direction on the screen.
  If Autodetection direction mode is Off, you must specify the next fragment of the raster curve on screen (fragment between two nodes or between a node and the end point of the raster curve).

TIPS: When tracing polylines you can use several input options: enter a key-letter in the command line, the cursor menu, or the Line Following panel buttons.

	Inverts the tracing direction
	Cancels the last tracing step
	Cancels the last polyline segment
	Allows the addition of a linear segment to a polyline without tracing. Several segments can be added with SHIFT pressed.
	Zooms the image to show the last added polyline vertex in the screen center
	Redraws the AutoCAD screen in the Line Follow mode

Tracing polylines with orthogonal segments

When tracing, you can obtain vector polylines with orthogonal segments. For example, this mode can be used to trace buildings on scanned maps.

The angle for orthogonalization can be estimated automatically or specified manually.

To obtain polylines with orthogonal segments:

Open the Trace tab of the R2VConversion options dialog. Select the Line Follow Orthogonalization checkbox. Select the Autoestimate Base Angle checkbox or specify the angle for orthogonalization in the Base Angle field or by the measure button.

Tracing Outlines

You can trace raster outlines. Tracing results depend on the selected parameters and mode of tracing. Tracing parameters are set in the Trace tab of the R2V Conversion Options dialog.

Setting parameters of tracing outline
- Auto Extend vectors: Off	Creates vector on two colors boundary.
- Auto Extend vectors: On	Creates vector at the center of raster line. IMPORTANT: Raster line width is specified with the Options tab of the R2V Conversion Options dialog.
- Export single contour: Off	Creates outer and nested outlines.
- Export single contour: On	Creates the outer outline only.
- Auto Extend vectors: On - Export single contour: On - Keep raster trace mode	Raster data inside the outline is kept.
- Auto Extend vectors: On - Export single contour: On - Erase raster trace mode	Raster data inside the outline is erased.

How to trace outlines

• Set the trace outline parameters.
• Specify the tracing mode (for example, Produce Vector and Erase Raster).
  See detailed information in section Tracing Modes and Commands.
• Run the Trace Outline command.
  If several available raster images are inserted into the drawing, a selection dialog box appears.
  
• Specify a point inside the outline.

Tracing Raster Symbols

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