topic Re: Create centreline from a polygon in ArcObjects SDK Questions

Create centreline from a polygon

GarySham — Wed, 19 Jan 2011 02:28:37 GMT

Dear all,

I am working on a project to create a centerline from a polygon automatically. The user select a polygon and click a button, the centerline will create for him.

I have tried the build-in function ???Collapse Dual Lines to Centerline???, but it cannot perform well so I decide not use this function in this project. In further study, I find out some terms such as ???Medial Axis???, ???Skeleton???, ???Voronoi polygon???, those are some concepts related to centerline formation. However, I find difficult to understand those algorithm.

Does anyone have a suggestion to me for this project?
Does anyone have a suggestion for how to implement those concepts in ArcMap?
Is there any sample script or algorithm I can refer to as reference?

Development language: C#, VB.Net
ArcGIS : ArcMap 9.3.1

Best regards,
Gary Sham

Re: Create centreline from a polygon

Venkata_RaoTammineni — Wed, 19 Jan 2011 03:54:56 GMT

Dear all,

I am working on a project to create a centerline from a polygon automatically. The user select a polygon and click a button, the centerline will create for him.

I have tried the build-in function �??Collapse Dual Lines to Centerline�?�, but it cannot perform well so I decide not use this function in this project. In further study, I find out some terms such as �??Medial Axis�?�, �??Skeleton�?�, �??Voronoi polygon�?�, those are some concepts related to centerline formation. However, I find difficult to understand those algorithm.

Does anyone have a suggestion to me for this project?
Does anyone have a suggestion for how to implement those concepts in ArcMap?
Is there any sample script or algorithm I can refer to as reference?

Development language: C#, VB.Net
ArcGIS : ArcMap 9.3.1

Best regards,
Gary Sham

http://arcscripts.esri.com/details.asp?dbid=15481

Re: Create centreline from a polygon

GarySham — Wed, 19 Jan 2011 04:43:01 GMT

Thank you Venkat Tammineni.

The sample software just focus on point layer, but I would like to use the polygon as a input data and generate a centerline for it.
Do you have any idea about this ??

I read some paper about �??Medial Axis�?�, �??Skeleton�?� and seem they are useful concept in this project. However, I cannot understand their algorithm and don't how to implement it.
Do you have any idea about this ??

Regards
Gary Sham

Re: Create centreline from a polygon

Venkata_RaoTammineni — Wed, 19 Jan 2011 05:18:05 GMT

Thank you Venkat Tammineni.

The sample software just focus on point layer, but I would like to use the polygon as a input data and generate a centerline for it.
Do you have any idea about this ??

I read some paper about �??Medial Axis�?�, �??Skeleton�?� and seem they are useful concept in this project. However, I cannot understand their algorithm and don't how to implement it.
Do you have any idea about this ??

Regards
Gary Sham

You may not directly ...but some how...

http://www.ian-ko.com/resources/howto.htm

http://www.ian-ko.com/ET_GeoWizards/UserGuide/createCenterlines.htm

http://www.crwr.utexas.edu/gis/archydrobook/DataModelFiles/Tutorial/ArcHydroPart1.htm

Re: Create centreline from a polygon

GarySham — Wed, 19 Jan 2011 06:25:17 GMT

Thank you for your suggestion.

I know there are some existing tools in the market can perform similar function. However I don't have resource to buy this tools and I cannot modify these tools. So I would like to implement it and fit to my project use.

Do anyone have ideas how to implement it or sample code/algorithm for reference ?

I find out some concepts (�??Medial Axis�?�, �??Skeleton�?�......) but have no idea how to implement it.

Regards,
Gary Sham

Re: Create centreline from a polygon

Venkata_RaoTammineni — Wed, 19 Jan 2011 07:58:14 GMT

Thank you for your suggestion.

I know there are some existing tools in the market can perform similar function. However I don't have resource to buy this tools and I cannot modify these tools. So I would like to implement it and fit to my project use.

Do anyone have ideas how to implement it or sample code/algorithm for reference ?

I find out some concepts (�??Medial Axis�?�, �??Skeleton�?�......) but have no idea how to implement it.

Regards,
Gary Sham

Check below thread it may help you...

http://forums.esri.com/Thread.asp?c=93&f=992&t=83405

Re: Create centreline from a polygon

GarySham — Thu, 20 Jan 2011 05:51:01 GMT

Actually, I have searched the esri forum before and find out some related posts. However, they are not very useful in my project. Therefore, I post a new post here to ask anyone for suggestions and ideas.

"http://forums.esri.com/Thread.asp?c=93&f=992&t=83405" seem not useful as it talk about how to construct a line perpendicular to centreline but not talk about how to from a centreline.

I have also gone through
http://forums.esri.com/Thread.asp?c=3&f=38&t=71339&mc=13#msgid190020
http://forums.esri.com/Thread.asp?c=3&f=38&t=71339&mc=13#190147
http://forums.esri.com/Thread.asp?c=3&f=38&t=76045

Regards
Gary

Re: Create centreline from a polygon

BradChappell — Thu, 20 Jan 2011 14:01:37 GMT

Try IPoint's ConstrainAngle and ConstrainDistance methods.

On first thought that's where I would start in calculating the vertices of the center line.

Re: Create centreline from a polygon

GarySham — Mon, 24 Jan 2011 05:29:24 GMT

Thank you for your suggestion.

I has studied these IPoint's ConstrainAngle and ConstrainDistance methods but don't know how to use these methods to compute the centreline.

Would you mind tell me how do you use these methods to compute the centreline?

Regards,
Gary Sham

Re: Create centreline from a polygon

RogerBrown — Thu, 03 Feb 2011 15:10:33 GMT

Gary,

I use the ArcGIS hydrologic flow models within point-density-rasters (or after the PDR is flipped upside down) to find medial axis.

You could form a point-density-raster (PDR) of all intersecting lines, where each line connects a pair of vertexes along the polygon perimeter, then apply a flow model for this PDR flipped upside down to find the "streams" that are candidates for the medial axis.

This sounds tedius but software to form this simple geometry (then threshold everything) could be written.

Hope this suggestion helps you.

Thanks,

Roger

Re: Create centreline from a polygon

MilesLoretta — Fri, 20 May 2011 20:26:04 GMT

If you need a quick fix to this issue, I figured one out. You have a polygon that's equally distant along its length from side to side, and you need a centerline quickly. Convert the polygon to a line, then do a buffer on one of the sides, then trim as needed. This is mainly for a long polygon like a ROW or road segment. Some of the other tools didn't work for me. I basically had a ROW segment, very long and 100' across. It winds so much that moving a side wouldn't work.