Topological Editing on Coverages: Dangle Length and Fuzzy Tolerence (Especially for GATE-Geospatial 2022)

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Dangle Length

Topological editing on coverage typically starts by constructing its topology.

The dangle length specifies the minimum length for dangling arcs on the output coverage. A dangling is such as an overshoot is removed if it is shorter than the specified dangle length.

Dangle Length

The dangle length can remove an overshoot if the overshoot, such as , is smaller than the specified length. The overshoot remains.

Fuzzy Tolerance

The fuzzy tolerance specifies the minimum distance between points and arcs on the output coverage. It is useful for removing duplicate lines within the specified tolerance.

Fuzzy Tolerance

The fuzzy tolerance can snap duplicate lines if the gap between the duplicate lines is smaller than the specified tolerance. In this diagram, the duplicate lines to the left of the dashed line will be snapped but not those to the right.

Examples of Editing Using Coverages

Some examples are listed in the following:

Editing Dangles

One can remove an undershoot by extending the dangling arc to meet with the target arc at a new node, and remove an overshoot by deleting the extension.

Duplicate Arcs

One solution is to carefully select extra arcs and delete them, and the other is to delete all duplicate arcs within a box and redigitize.

Wrong Arc Directions

One can alter the direction of an arc by flipping the arc, thus changing the relative position of the beginning and end nodes.

Pseudo Nodes

One can remove a pseudo node by setting the two arcs on each side of the node to have the same ID value before unsplitting them.

Label Errors

One can add new label points with proper IDs for missing labels in polygon coverage. Multiple labels may also indicate an unclosed polygon.

Reshaping Arcs

To reshape an arc, one can move, add, or delete points that make up the arc.

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