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 Заголовок сообщения: How to adjust polygonal coverages?
СообщениеДобавлено: Ср апр 22, 2009 9:17 am 
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To adjust two polygonal coverages, one should select one of them as more reliable and to change the second one.

A simple example. Let us lay out a polygonal road through a wood. We draw the line of the road, then form a band polygon along it and SUBTRACT (cut out) this polygon from the polygon of the wood.

It is worse if the road polygon was cut out previously. We know its exact GPS position but there will be unwanted chinks if we subtract the polygon now.

The situation is not so awful if the chinks are small and you have Easy Trace v. а 8.5. Use the Topology Correction utility. Specify “Roads” as a reference layer and “Wood” as a layer to be corrected. Select the option “Adjust polyline edges within the radius” – and that’s all.

If you have an earlier version or the chinks are rather wide, you will not be able to avoid manual labour. Start the Check Polygons utility and search for holes. The utility will create bung polygons on the _ERRORS_ layer.

They will not merge with the wood of their own of course. Select the wood polygon with the Editor and in the summation mode (E) specify all these bungs. Just in a case, freeze the “Roads” layer before the operation.

It is useful to apply Topology Correction before you start Topology Check-up, even if it can not adjust polygon boundaries in your version. The “Contract vertices within given radius” option may "mend" most troublesome thin chinks.


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 Заголовок сообщения: Re: How to adjust polygonal coverages?
СообщениеДобавлено: Ср апр 22, 2009 9:18 am 
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Зарегистрирован: Вт мар 18, 2003 11:16 am
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And how to subtract roads from the wood?

It is easy... in v. 8.6 – just apply the Subtract Polygons utility. The operation is more difficult in earlier versions…

The point is that Shears (the main cutting tool) was repeatedly improved and alternated. It got new abilities from one version to another:

- An existing contour may be selected as a cutting frame at pushed Ctrl key;
- Shears «snatch» borders of polygons selected with Group Editor;
- Explicit specification of layers that may be cut became possible;
- Significant acceleration of cutting-out of holes;
- «Self-annihilation» of nested polygons on the cutting frame layer is corrected.

I don’t remember now in what version one or another improvement was done.

First of all you must specify exactly what to cut. Switch off all unnecessary layers and FREEZ the cutting one to avoid its self-distraction.

Or select the “victim” layer explicitly in the Parameter Bars of the Shears tool.

Create cutting frames or just select them (if possible) with the Group Editor and press Alt+W. Otherwise select the contours with the Shares holding the Ctrl key pushed. It is better to do in several movements. Make the cutting polygons transparent and polygons on the underlying layer – filled to see where holes will be.

:!: :!: :!: Make a copy of the ENTIRE PROJECT FOLDER including DB before cutting necessarily. Something may go wrong at first attempt!


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 Заголовок сообщения: Re: How to adjust polygonal coverages?
СообщениеДобавлено: Ср апр 22, 2009 9:18 am 
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Зарегистрирован: Вт мар 18, 2003 11:16 am
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What to do if the operation takes too much time?

Your version is rather old. You may only attribute cutting polygons to different layers. The old algorithm dully compared every cutting polygon with every “victim” – just a square algorithm and nothing more.

So, the operation will be four times faster if you halve the number of cutting polygons, etc.


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