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Polygon operations

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Polygons in Easy Trace are closed lines belonging to any layer marked as polygonal. The following operations are provide for polygons.

Polygon forming out of boundaries of other polygons and/or polylines snapped to them.

Polygon forming out of existing boundaries is accessible in the autoclose mode only. For example, we have a polygon representing a building and lines of lawn boundary that join its both sides.

To vectorize the polygon of the lawn, act as following:

  • select the tracer;
  • make the Lawn layer current;
  • click the first and the second point of lawn joining to the building.
The program confirms successful polygon forming by brief blinking of its boundary.

To create a "pipe-like" polygon (street part between two buildings for example), you may:

  • temporary "stopper" one end of the "pipe" with a line segment attributed to any layer;
  • form the polygon that will close another end of the "pipe" automatically;
  • delete the temporary "bung".

Merging (joining) of neighboring polygons.

To be available for joining, the polygons should have a common boundary.

  • select one of the polygons with the Editor;
  • press the ? key (or in the Editor's submenu);
  • click the second polygon.
If the polygons belong to the same layer but their attributes differ, the program suggests to select attributes for the resulting polygon. If the polygons belong to different layers, the joined polygon will be attributed to the layer of the polygon you selected first.

Polygon division in two parts.

Polygon division is accessible in the autoclose mode only. To do it, act as following:

  • select the tracer;
  • make the target polygonal (!) layer current;
  • draw a line crossing the polygon. Its first and last vertex should be snapped to the polygon borders;
  • input attributes of the cut off part.
The program confirms successful polygon division by brief blinking of the smaller polygon's borders.

If the initial polygon and the cutting line belong to different layers, the cut off (smaller) polygon will be attributed to the layer of the line. It does not inherit attributes, they should be input manually.

"Hole excision" in polygons (polygon subtraction).

Start state - two polygons, the smaller one is entirely within the bigger. To cut it out, act as following:

  • select outer polygon with the Editor;
  • press the W key (or in the Editor's submenu);
  • click any point WITHIN the smaller polygon (not its boundary!).
Do not put attention on the bridge between the inner and outer polygons - it will be ignored at export into your target system.

Subtraction allows correct boundary forming for overlapping polygons.

Editing of common boundaries.

Use the Topology Editor for this operation. This tool is convenient when you want to correct geometry of snapped objects. It changes position of a common vertex (node) of several snapped objects simultaneously, regarding them as one! It is equally easy to add and delete vertices of common boundaries.

Generation of inscriptions out of attribute values of polygons.

Text inscriptions, even if unnecessary in the project, may be extremely useful at attribute input control and visual checking. Inscriptions generated within orthogonal objects are automatically centered and aligned along long sides of rectangles.

See Utilities->Database->Generate Inscriptions.

Polygon filling - switching on/off.

When the Fill Polygons view mode is on, closed polylines belonging to polygonal layers are filled with colors. This mode simplifies visual control of polygonal objects - it is easy to detect unclosed polylines, slits between polygons and undigitized yet areas. Neighboring polygons attributed to the same layer may be filled with different tints of a color that makes it easy to tell one of them from another. You may also use "transparent" filling allowing to see the image and vector entities under the polygon.

If polygons of one layer may overlap polygons of another layer, their correct representation in the Fill Polygons view mode demands correct order of layers in the layer list. Upper layers of the list will be drawn above lower ones.

Use the F4 hot key to switch polygon filling on/off quickly.

Border and filling representation depending on the polygon's attribute.

To use the Thematic Displaying view mode, you should first attach attributive values to line types and different fillings. Thematic representation may be attached to only one field of the object's table of attributes. It simplifies visual control of attribute values you input. Once done, the setting will be inherited by all prototype-based new projects. To do the setting, act as following:

  • open the Project Layer Settings dialog box (for example, press the Ctrl-L key combination);
  • click twice the name of the attribute table of the desirable layer;
  • tick the check box in the Active column to select the field that will determine representation of polygons;
  • click the Visualization... button to open the Attribute Display settings dialog box;
  • make the settings of line types and fillings for every possible value of the selected attribute.

Topology checking for a polygonal cover.

The program has integrated means for topological accuracy checking applying different criteria. For polygonal covers it implies search of slits, overlappings and other specific mistakes.

See Utilities->Topology->Check Polygon Cover.

The utility creates closed lines (polygons) on the _ERRORS_ layer contouring found mistakes. If the _ERRORS_ layer is missing in the project, it will be generated automatically placed first in the layer list.

Correction of topological errors should be done manually with the help of the Editor or Topology Editor. Zoom in the image to simplify correction and apply the F and V keys for navigation from a corrected error to the next/previous one.

Band polygon forming with a specified width along specified lines.

Only one boundary of roads' traffic areas is represented sometimes in topographical maps, or even their canter lines without boundaries at all (most often - for roads without asphalt covering). Usually, they add the missing boundary manually to represent the road as a band of fixed width. This and similar operations are automatized in Easy Trace.

See. Tools->Band Polygon.

Other operations.

All operations provided for polylines are applicable to polygons: you may edit, cut, close/unclose, move, rotate, copy and duplicate them. Use the Editor to fulfill all these operations.

Note, that displacement of polygon vertices may form slits in the polygon cover!

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