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TIP OF THE WEEK

Converting Polygons to Lines

When converting to lines, Feature Analyst® determines the points closest to the center line of each polygon, links them with arcs, and returns a line layer. This function is helpful when extracting elongated features such as rivers and street networks, where full polygon coverage is unnecessary.

The Convert to Line dialog box provides the following options:

OPTION	FUNCTION
Polygons represent road networks	If your polygons represent a network of roads, check this option. Feature Analyst will process the conversion taking into consideration that the roads make up a network. The system processes the segments, as much as possible, setting straight lines and 90° angles. Note: this option is not recommended when extracting rivers or rural roads.
Gap jumping distance	Use this setting to jump gaps in segments that should be attached. You may also use the default setting to allow Feature Analyst to determine the proper gap jump distance.
Remove dangles with length less than	Use this setting to remove short segments or dangles on your line features. You may also use the default setting to allow Feature Analyst to determine the length of dangles to remove.
Rework intersection segments whose length is less than	Use this setting to repair intersections. You may also use the default setting to allow Feature Analyst to determine the length of intersection segment to repair.
Smooth results	Select this option if you want to smooth the line results. Smoothing removes vertices that deviate from the optimum center line. Select the option and accept the default settings. Or, select the option and choose Smooth Settings to customize your smoothing options.

Often times your extracted features are better represented by lines instead of polygons, as shown in the below image. Whenever this is the case, take advantage of the Feature Analyst software's Convert to Line tool.

In the above scenario, the streets were extracted in polygon shapes and then converted to lines using the following steps:

Highlight the final polygon results later in the Table of Contents.
Select Post Processing from the Feature Analyst drop menu and choose Convert to Line.
Set the following options in the Convert to Line dialog box:

Select the Polygons Represent Road Networks check box.
In the Gap Jumping Distance field, enter 30. This tells Feature Analyst to jump any gap less than 30 pixels wide.
In the Remove Dangles field, enter 85. This tells Feature Analyst to delete any dangle or line spur shorter than 85 pixels long.
In the Rework Intersection field, enter 5. This tells Feature Analyst to rework any intersecting segment less than 5 pixels long.

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Feature Analyst Tips:

Creating a Training Set

Input Representation

Aggregation

Masking by Layer

LIDAR Analyst Tips:

3D Building Extraction