Autodesk 05726-091452-9060 User Guide - Page 140

Raster Selection Parameters

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9 Working with Raster Selection Raster Selection Parameters Raster selection is affected by three parameters in the Options tab: Max Width, Max Break and Approximation Accuracy. Max Width Defines the maximum width of raster objects that can be selected with the methods based on Object Type Recognition and Line Following. The program does not select lines with widths larger than the specified value. Max Break Defines the length of the largest break to be ignored in a raster line. If raster line breaks are less than the specified value, then upon selection the line breaks will be eliminated, and the line will be chosen as an entire raster object. Approximation Accuracy When selecting raster, using the methods based on the Object Type Recognition, Approximation Accuracy defines the accepted deviation of raster object symbols from their vector prototypes. If the original raster lines are distorted (For instance, raster circles are elliptical.), then you can improve the selection accuracy by moving the Approximation Accuracy slider to the left (Rough). If the original raster image is high quality, then move the slider to the right (Fine). Forced selection is also influenced by the Auto Extend Vectors mode, which is toggled in the Trace tab of Conversion Options dialog (see page 188). You can measure the Max Width and Max Break values directly from a raster image. To measure Max Width on an image 1. Click the button next to Max Width. 2. Specify two points in the raster image so that the line connecting these points crosses the thickest part of the raster line. The program defines the Max Width value equal to the length of the line part that covers the raster object. To measure the Max Break value on an image 1. Click the button next to Max Break. 2. Specify two points in the raster image so that the line connecting these points crosses the largest break in the raster line. The program defines the Max Break value equal to the length of the line part that covers the raster background. 143

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9 Working with
Raster
Selection
143
Raster Selection Parameters
Raster selection is affected by three parameters in the
Options
tab:
Max Width
,
Max
Break
and
Approximation Accuracy
.
Max Width
Defines the maximum width of raster objects that can be
selected with the methods based on
Object Type
Recognition
and
Line Following
. The program does not
select lines with widths larger than the specified value.
Max Break
Defines the length of the largest break to be ignored in a
raster line. If raster line breaks are less than the specified
value, then upon selection the line breaks will be eliminated,
and the line will be chosen as an entire raster object.
Approximation
Accuracy
When selecting raster, using the methods based on the
Object Type Recognition
,
Approximation Accuracy
defines
the accepted deviation of raster object symbols from their
vector prototypes.
If the original raster lines are distorted (For instance, raster
circles are elliptical.), then you can improve the selection
accuracy by moving the
Approximation Accuracy
slider to the
left
(Rough).
If the original raster image is high quality, then
move the slider to the right (
Fine
).
Forced selection is also influenced by the
Auto Extend Vectors
mode, which is
toggled in the
Trace
tab of
Conversion Options
dialog (see page 188).
You can measure the
Max Width
and
Max Break
values directly from a raster
image.
To measure Max Width on an image
1. Click the button next to
Max Width
.
2.
Specify two points in the raster image so that the line connecting these points
crosses the thickest part of the raster line.
The program defines the
Max Width
value equal to the length of the line part
that covers the raster object.
To measure the Max Break value on an image
1. Click the button next to
Max Break
.
2.
Specify two points in the raster image so that the line connecting these points
crosses the largest break in the raster line.
The program defines the
Max Break
value equal to the length of the line part
that covers the raster background.