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Extract Linear Features with Intelligent Digitizer

Extract Linear Features with Intelligent Digitizer

Use Intelligent Digitizer to extract linear features such as roads and rivers as vector data. You select features using intelligent mode, where you place seed points along the path of a feature and ENVI automatically finds the intermediate points. The Intelligent Digitizer is particularly useful for images that have low spectral content, but high spatial resolution, such as high-resolution imagery from QuickBird, IKONOS, and OrbView-3.

ENVI supports polyline vectors for use on features such as roads, and supports polygon vectors for use on features such as lake boundaries. You can extract features using a single band, or you can extract them using multiple bands. Using Intelligent Digitizer on properly-selected multiple bands increases the accuracy of your results.

Intelligent Digitizer is a semi-automated tool, where you manually select seed points along the path of a linear feature and ENVI automatically finds the nodes in between. You can undo and redo seed points as you define them, and snap features with one another when they are within a certain proximity. You can also toggle between intelligent mode and ENVI’s standard vector tool mode when needed, such as when contrast is low or there are big disturbances in the features, to ensure that feature selection is accurate.

With automatic post-processing operations, you can establish intersections between crossing segments of features so they share a vector node, and you can correct polylines that overshoot their intersection with other polylines. With manual post-processing operations, you can snap polylines to one another, extend existing polylines in intelligent mode, and calculate the length attribute for features.

Because Intelligent Digitizer is integrated with ENVI’s vector tool, standard vector functions are available to manually edit extracted features, to add and edit feature attributes, and to export layers to shapefiles.

See the following sections:



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