topic Re: Creating polygon feature with parallel sides? in Data Management Questions

Creating polygon feature with parallel sides?

BärbelHorat — Thu, 30 Jun 2011 11:07:54 GMT

I re-post a problem from 2006. Please see below. Has there anybody find a way?

Thanks for your reply!
Matthias
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Re: Creating polygons with parallel sides on the fly?
Author J.M.
Date Jul 03, 2006

I am trying to digitize a series of georeferenced tif's depicting steam tunnels into a polygon feature class. Ultimately I would like the polygons to be of a uniform thickness and for the two sides of the tunnel to be exact copies of each other.

I am looking for a way to do that without having to create lines, and then perform some geoprocessing on those lines to create a polygon from them. I would like to be able to simply draw one series of segments that makes up one side of the tunnel, and then trace that side with some specified offset to complete the polygon.

Any thoughts?

Thanks!

Re: Creating polygon feature with parallel sides?

Anonymous User — Thu, 30 Jun 2011 15:57:35 GMT

The rectangle construction tool in 10.0 is the easiest way to do this.

You can also use the polygon construction tool in 10.0 or the sketch tool in 9.x with a polygon target by using sketch constraints, deflection, then square and finish on the context menu's if you want to manually create rectangles. This method would also have worked in 2006.

Re: Creating polygon feature with parallel sides?

BärbelHorat — Fri, 01 Jul 2011 08:13:10 GMT

Thank you Sean

I am sorry for not making myself quite clear.

J.M. and me are not interested in drawing simple rectangles but polygons with one side having a parallel side on its opposite.

In my example, I aim to digitize rivers that curve and meander. Their width should remain constant along the riverpath.

One could digitize the centre line as a polyline and then buffer this line to get a polygon. However, I wonder whether there is a more straight-forward method (i.e. to directly construct a curved polygon with a constant width).

By the way, I am using ArcGIS 10, SP1.

Further help will be higly appreciated.

Kind regards,
Matt

Re: Creating polygon feature with parallel sides?

Anonymous User — Fri, 01 Jul 2011 16:22:14 GMT

Hi Matt,

Ok, now i understand.

If the river doesn't already exist then digitizing into a line layer and buffering that would be the easiest option. You can use the editor buffer command but it only creates round ends.
If you were placing a polygon that followed an existing river you could capture directly into a polygon layer using trace and trace offset (the o key) to get both sides of the polygon following the river.

Re: Creating polygon feature with parallel sides?

BärbelHorat — Mon, 04 Jul 2011 09:56:17 GMT

Hi Sean

I hoped there might be a way that does without a pre-existing feature.

It's pity, but thanks anyway.

Matt

Re: Creating polygon feature with parallel sides?

GeorgeOliver — Tue, 10 Jul 2012 20:00:55 GMT

A work-around I've been using is to first create a polygon, accurately digitizing one side of the feature (i.e., the tunnel). Finish the polygon roughly. Then use the Reshape Feature tool and trace the accurately digitized side to replace the rough side, using an offset corresponding to the width of the feature you want to digitize. Because the "Reshape Tool" feature requires your sketch's endpoints to cross the polygon on both sides, it may be useful to start your sketch using the "Straight Segment" tool, since the offset of the Trace tool may only allow a segment that won't cross the polygon edge. One very useful shortcut is the tab key--if the Trace tool traces on the wrong side of the polygon, you can toggle sides with the tab key.

It's a bit of a mouthful, but once you get the hang of it, it works quite well.

George