Field

Description

Method

There are currently five methods to choose from for automatic polygon creation.

The first four methods use a radial approach. A point is picked inside the structure. Then the edge is searched for in several directions that radiate from the initial pick. (The number of directions is specified in the # of Points field.) These methods use different criteria for finding the edge:

• Biggest Change compares successive adjacent sampling areas for average intensity from Min Reach data points from the center to Max Reach and uses the biggest change.

• Percent Change compares successive adjacent sampling areas for average intensity starting at Min Reach data points from the center and stops when the entered % Change difference is found. If it is not found by the time the Max Reach is reached, it uses Max Reach.

• Rate of Change compares successive triplets of adjacent sampling areas for average intensity from Min Reach data points from the center to Max Reach and uses the position where the rate of change is the highest.

• Change from Center compares successive sampling areas to the Original Picked Point sampling area for average intensity starting at Min Reach data points from the center and stops when the entered % Change difference is found. If it is not found by the time the Max Reach is reached, just use Max Reach.

The fifth method, Tracer % Change, uses the radial criterion of Change from Center for the first point only. Then it follows the structure around using a search based on the previous point and the current direction of points made so far to define the structure.

Change

Defines the kind of percent change you are looking for. Use the option list to select whether this change should be an increase or a decrease (or either) from the comparison value.

Number of Points

For the first four methods, Number of Points specifies how many points should be used to surround the structure. For the Tracer method, Number of Points is the minimum number of points that are required to define the structure. If the resulting number of points is less than this number, the polygon is not created.

Sample Size

When searching for the change in intensity, a local mean is obtained for each position. The size of the area measured is the square of the Sample Size.

Step Size

Defines how far apart the points will be. This is used for the Tracer % Change method only.

Min Reach

Specifies a distance from the center point to begin the outward search for intensity change. This avoids finding a structure that is closer to the picked point than the desired structure.

Max Reach

Sets a limit for how far to search for the structure from the picked point. This avoids other structures and prevents futile searching when a structure is not found.

Max Length Diff

The biggest allowable difference for length of vectors between a point and the center for two adjacent points. This helps to avoid making horribly wrong points when the criterion cannot find a structure.

Extend

Once the edge is found, the actual point can be placed a specified distance from that edge. A negative number puts the points inside the structure, and a positive number puts the points farther out from the structure.

Auto-smooth

Automatically smooths out any jagged edges from the polygons.

Automatic Polygon Propagation

Do Current Section uses points from a different section as seeds for new polygons in the current section. There are two methods for getting the seed points:

• If Using Last Picked Point is selected, the last point that was picked for each polygon in the reference section is used.

• If Using Last Picked Point is not selected, the center of gravity for each polygon in the reference section is used.

Do Whole Volume starts from the reference section to create polygons in the next higher and next lower section. It repeats this process for all of the sections,  using the centers of polygons in the section prior to the current one. You can use Auto Pick File to read in a file of points as seeds for each section.

Using Z/W/T

Allows you to use polygons in a section as seeds for creating new polygons in another section. Enter the Z, wavelength, and time point of the "seed" section.

Use

To...

spacebar

Close a polygon

"e"

Delete the last point

"s"

Smooth out a selected polygon

"f"

Smooth a selected polygon one step at a time

"a"

Delete a selected polygon

"d"

Delete the last polygon

"t"

Apply the template to the current section

"1"

Change to SelectPolygon mode

"2"

Change to CreatePolygon mode

"3"

Change to InsertPoint mode

"4"

Change to AutoPolygon mode

Use

To Choose...

Z

Biggest Change method

X

Percent Change method

C

Rate of Change method

V

Change From Center method

B

Tracer method