topic Re: Buffer distance not correct in ArcGIS JavaScript Maps SDK Questions

Buffer distance not correct

DanikBourdeau2 — Tue, 28 Jan 2014 07:43:53 GMT

Hello,

I'm having difficulty creating an accurate buffer of a polygon. I can request the buffered geometry and display the respective graphic just fine, but when I measure the distance of the buffer to the original polygon (using the esri measure dijit) the distance is not the same as my input distance.

When in ArcMap, I buffer the same polygon by the same distance and I get a different buffer than I get from the js Geometry Service so I'm fairly certain that my problem lies with the Geometry Service not the Measurement dijit.

var buffDist = dom.byId("BuffDist").value; var gph = graphicArray[0]; var gs = new GeometryService("http://tasks.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer"); var params = new BufferParameters(); params.distances = [buffDist]; params.unit = GeometryService.UNIT_KILOMETER; params.bufferSpatialReference = map.spatialReference; params.outSpatialReference = map.spatialReference; params.geometries = [gph.geometry]; gs.buffer(params, function (result) {});

My workflow is quite standard. My input geometries are from a graphic that I received from a user click on the map. The map spatial reference is web mercator (102100), which I thought might be causing the problem so I have been experimenting with converting web mercator to geographic but I have not had any luck getting a successful return from the Geometry Service.

Anyone have any ideas what is causing the buffer to be wrong?

Re: Buffer distance not correct

JianHuang — Tue, 28 Jan 2014 18:52:52 GMT

The geodesic parameter should be true when performing a buffer under web mercator.
https://developers.arcgis.com/javascript/jsapi/bufferparameters-amd.html#geodesic

Re: Buffer distance not correct

DanikBourdeau2 — Tue, 28 Jan 2014 23:59:31 GMT

Hi Jian,

I failed to mention that I had tried setting the geodesic parameter to true but it still does not give me a proper buffer. I wasn't sure if Web Mercator should have the geodesic parameter set to true since it's listed as a projected coordinate system here?

I took some screen grabs to help illustrate what's going on. The first image is from my web app where I'm buffering using the js api, same parameters as above except that I have now added geodesic=true. The second image is from ArcMap where I have buffered the same polygon by the same amount, 100km. I placed the same basemap under both images to show some context.

[ATTACH=CONFIG]30923[/ATTACH]

[ATTACH=CONFIG]30924[/ATTACH]

Re: Buffer distance not correct

JianHuang — Wed, 29 Jan 2014 00:39:24 GMT

Danik,

What does the json request look like?

Re: Buffer distance not correct

DanikBourdeau2 — Wed, 29 Jan 2014 00:57:05 GMT

This is the request i send out to the buffer service. Is this what you are looking for?

[ATTACH=CONFIG]30925[/ATTACH]

Re: Buffer distance not correct

JianHuang — Wed, 29 Jan 2014 01:57:57 GMT

The geometry service you are using on tasks.arcgisonline.com is version 10.04, which doesn't support geodesic parameter. Please try this:
http://sampleserver6.arcgisonline.com/arcgis/rest/services/Utilities/Geometry/GeometryServer/buffer
Please note, either services serve the purpose of just samples. It should not be part of your product code.

Re: Buffer distance not correct

DanikBourdeau2 — Wed, 29 Jan 2014 02:06:09 GMT

Thanks Jian, that makes more sense now.

I'm a bit confused. I thought we could use tasks.arcgisonline.com for production apps? We have an organizational license for ArcGIS Online where we host all our feature services. We tend to develop our own apps in house rather than use arc online's mapping interface. Which Geometry Service should we be using?

Re: Buffer distance not correct

JianHuang — Wed, 29 Jan 2014 02:10:07 GMT

Danik,

Sorry for the confusion. I'm not the best person to answer the licensing question. You may want to contact Esri Support. But samplerserver6 definitely is just a 'sample'.

Re: Buffer distance not correct

DanikBourdeau2 — Wed, 29 Jan 2014 02:22:08 GMT

No worries. I may post something in the arc online forums and see what I get.

I just changed the Geometry Server to sampleserver6 and everything worked like a charm. Thanks very much for your help.