9 Working with
Raster
Selection
133
The figure shows that the program has
selected the part of the raster line until it
meets the intersection with the other
raster objects.
To select a part of a raster polyline between two nodes
1. At the
rSelect
command prompt enter
j
for the
obJect
option.
2. Click on a point of the raster line that is between these nodes.
Selecting Raster Entities
Raster entities
are raster objects with the same shape as basic vector objects –
vector image entities. From here on we shall use the terms
raster circle
,
raster arc,
and
raster line
to imply raster objects that have a shape of a circle, arc, or line.
However, you should note that real raster entities might have defects that hamper
their identification by the program such as breaks, elliptical arcs and circles, varying
width, etc.
If the
Type Recognition
selection type is set, then the
Object
method can handle
both
raster lines
and arbitrary raster objects with approximately equal width and
length.
When a raster line is picked, the program identifies the type of raster entity (line, arc
or circle) and then tries to select the object of the greatest possible size. It ignores
the points of intersection with other objects, and the selection extends until the
symbol of the selected object becomes identical to the entity recognized. Since real
raster objects may differ from ideal raster entities, the recognition algorithm uses
the
Approximation Accuracy
parameter. This parameter defines the accepted level
to which the real raster objects may differ from the ideal ones. For a description of
the
Approximation Accuracy
parameter
refer to “Tuning Selection ” on page 142.
Selecting a raster entity preserves its intersections with other objects. Therefore,
transforming and deleting raster data selected when
Object Type Recognition
is on
does not create break in remaining raster objects. This allows you to process raster
data in the same manner as you process vector objects. For example, deleting a
raster line that crosses the circle leaves the circle intact in the image, exactly as it
would when you delete a vector line that lies over a vector circle.
In case the raster object selected is not a raster line, the program detects its
boundary and selects the object. An arbitrary raster object width should be greater
than the maximum allowed width of a raster line.
*
To distinguish raster lines from other raster objects the program uses the
reference value of the maximum accepted raster line width. For
