Centre line of polygon

[AndrewMcClune]

I am trying to create a network from a set of polygons of roads, paths railway and water-ways. Does anybody know how to find the centre line of a polygon so that it will, for example, represent the centre line of a road.

Thanks

[KeaganAllan]

I am trying to create a network from a set of polygons of roads, paths railway and water-ways. Does anybody know how to find the centre line of a polygon so that it will, for example, represent the centre line of a road.

Thanks

Hi Andrew,

I am not sure if you are familiar with ET Geowizards?
This set of tools is extremely useful for performing these types of tasks. It can be downloaded from www.ian-ko.com.

Looking at my version there is a tool that would allow you to generate a centerline from your polygon features. Copying straight from the help file it states:

Creates centerlines from polygon features.

Inputs:

A polygon feature class. 
Centerline type:

Inside - the centerlines will be created inside the polygons - suitable for deriving centerlines from rivers and streets represented by polygons

Outside - the centerlines will be created in the gaps between polygons - suitable for deriving street centerlines from cadastral data.

Outputs:
New  polyline feature class

I hope that helps, if not I am sure we can figure out a way.

Cheers,
K

[AndrewMcClune]

Brilliant that is very helpful

However is this tool in the free ET GeoWizards package. Having a look around the website it says that 'ET GeoWizard is not a free program' and unfortunately I am not able to purchase the full package

[KeaganAllan]

I think if your input file has less than 300 or 100 features then it is ok (what you can do is look at dissolving your input layer into a single feature and then split your output shapefile at a later stage).
The program is free to use, just to unlock the full features you need to purchase it.

Even if you are unable to purchase it, I highly recommend you download it, it has so many other useful tools that can speed up how you do things.

[AndrewMcClune]

Ok great. Thanks for the help Keagan

[KeaganAllan]

No problem.

good luck

[AndrewMcClune]

Having a few problems trying to run the polygon create centerline function. I can get as far as inputting the maximum and minimum width and from there I cannot go any further. It says that it is an unlicensed function. Do I therefore need to request the key or register the product, and if I do will there be any cost?

Thanks

[KeaganAllan]

How many features are there in your input file?
You could try a dissolve first to get them into a single feature and then try and run it.

Unfortunately I have not had much experince using that function in ET.
If that does not work, then a new way would potentially have to be used...I will give it some thought...

[AndrewMcClune]

I don't think it is effected by the number of input features. I have dissolved the polygons together to get an overall data set of 291, from an original 1974 but it still says it is an 'Unlicensed function'. I think the problem is that it is not registered so I may therefore need to register the product, hopefully at no extra cost. I will look into this.

Thanks anyway,

Andrew