topic Re: Best way to get data from World Topo Map service in ArcGIS JavaScript Maps SDK Questions

Best way to get data from World Topo Map service

DougCollins — Thu, 19 Dec 2013 15:23:42 GMT

I am trying to use the Elevation Layer (either m or ft) from the World Topo Map service (http://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer) to get elevation values. However, this is a Raster layer, and I don't see any way in the JavaScript API to get or query the values. Maybe I have missed something, and sure would like to know about it.

Everything I have seen so far uses Feature Layers to query or retrieve data. This is easy to do in ArcMap, but I can't see how to do it using the JavaScript API.

Does anyone have information that would help with this problem?

Thanks for your time!
Charlie

Re: Best way to get data from World Topo Map service

JianHuang — Thu, 19 Dec 2013 16:13:39 GMT

topo map service is only for creating tiled map layer. What you are looking for is elevation profile service, which is a GP service.
This is an old sample service:
http://sampleserver2.arcgisonline.com/ArcGIS/rest/services/Elevation/ESRI_Elevation_World/GPServer/ProfileService
I'm not sure about the latest one. Please ask the question on AcGIS REST API forum.

Re: Best way to get data from World Topo Map service

DougCollins — Thu, 19 Dec 2013 18:51:17 GMT

Jian,
I am not trying to create an elevation profile. All I want to do is click a point on the map and get the elevation of that point. It seems like it should be as simple and basic as getting the latitude and longitude of a point on the map.

Layers 1 and 2 of the World Topo Map service indicate that they are Elevation (m) and Elevation (ft). One would think that this service could be used for getting the elevation. However, if that is not the case, and the elevation profile service is the answer then how does one get the elevation of a single point? That service does not seem to provide that.

Thanks,
Charlie

Re: Best way to get data from World Topo Map service

SteveCole — Thu, 19 Dec 2013 20:35:43 GMT

I think you want to use the IdentifyTask to query the raster (your choice- either the feet or meters service) and retrieve your value that way. Have a map OnClick event and then pass the geometry of the clicked location (make sure they are in Web Mercator projection) to the geometry property of the IdentifyParameters. I think this will return what you're looking for.

Steve

Re: Best way to get data from World Topo Map service

JianHuang — Fri, 20 Dec 2013 02:38:04 GMT

If you have an ArcGISImageServiceLayer, identifyTask (after JS API 3.5) can find the pixel value and other related info, which might be the elevation depending on the data. But topo map is a tiled map service.

Re: Best way to get data from World Topo Map service

DougCollins — Fri, 20 Dec 2013 11:38:09 GMT

Thanks for the info. I will try the IdentifyTask to see what it provides.

Currently I am using version 3.2 so I won't be able to take advantage of the ArcGISImageServiceLayer yet. I will need to upgrade other components of my site as well to move to the latest version of the JS API.

Thanks,
Charlie

P.S. I tried to give both Steve and Jian credit for their answers but it only let's me select one. 😞

Re: Best way to get data from World Topo Map service

JohnGravois — Mon, 23 Dec 2013 14:59:32 GMT

just to clarify. the World Topo Map is one of the few tiled map services that i know of that actually exposes a few underlying layers to operations like Identify:

http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/identify?geometryType=esriGeometryPoint&geometry=-117,34&sr=4326&layers=&time=&layerTimeOptions=&layerdefs=&tolerance=3&mapExtent=-13419896.181968385,3741133.9123886316,-12717898.514197363,4243783.810391926&imageDisplay=500,500,96&returnGeometry=true&maxAllowableOffset=&f=HTML

[ATTACH=CONFIG]30076[/ATTACH]

Re: Best way to get data from World Topo Map service

TammyBearly — Tue, 25 Feb 2014 21:42:30 GMT

As of February 24 when this service was updated, I can no longer identify the elevation.
I was using field name Pixel value for layers 1 and 2. What can I use instead?

Re: Best way to get data from World Topo Map service

JohnGravois — Tue, 25 Feb 2014 21:54:38 GMT

hi tammy,

it looks like this has been documented. im not sure of the reason for the change.

i know we have more robust elevation services in beta, but that seems a bit overkill compared to what you were doing before.

Re: Best way to get data from World Topo Map service

SteveCole — Tue, 25 Feb 2014 22:11:48 GMT

The reason for the change seems quite clear to me- the free ride is over. Just like what happened with routing at the end of last year, ESRI wants to now lock you into paying for these services using ArcGIS Online accounts & credits.

ESRI still provides two elevation globeserver REST endpoints but probably not at the resolution you want:
http://services.arcgisonline.com/arcgis/rest/services/Elevation

Looks like you'll either have to a.) pay for credits & use ESRI's previously free service, b.) load up and serve your own elevation data, or c.) hope that the USGS or other fed agency is already serving up elevation data as a REST service someplace.

Re: Best way to get data from World Topo Map service

TammyBearly — Tue, 25 Feb 2014 23:14:40 GMT

Thanks for the reply.

I tried both of the globeservers and cannot get them to work.

How do the credits work and how much is the service?

The reason for the change seems quite clear to me- the free ride is over. Just like what happened with routing at the end of last year, ESRI wants to now lock you into paying for these services using ArcGIS Online accounts & credits.

ESRI still provides two elevation globeserver REST endpoints but probably not at the resolution you want:
http://services.arcgisonline.com/arcgis/rest/services/Elevation

Looks like you'll either have to a.) pay for credits & use ESRI's previously free service, b.) load up and serve your own elevation data, or c.) hope that the USGS or other fed agency is already serving up elevation data as a REST service someplace.

Re: Best way to get data from World Topo Map service

JohnGravois — Wed, 26 Feb 2014 15:53:17 GMT

tammy,
apparently the appropriate replacement service can actually be found here.

its my understanding that even though the service requires an ArcGIS Online subscription (which is now included with the purchase of ArcGIS Desktop automatically) it doesn't actually burn credits.

as a developer, what this means to you is that you'll have to authenticate on behalf of end users to access the content if you don't want anyone to have to sign in. this would entail setting up our new resource-proxy and either registering your app or storing hardcoded user credentials and routing traffic to the elevation service through your proxy.

this is similar to what you'd do if you were interested in using other Esri services like traffic, batch geocoding or routing.

Re: Best way to get data from World Topo Map service

TammyBearly — Wed, 26 Feb 2014 16:58:00 GMT

Hi John,

If I get the proxy service set up correctly, would I use the same identify task parameters. I will use the new url, http://elevation.arcgis.com/arcgis/rest/services/WorldElevation/Terrain/ImageServer. But should the field still be Pixel value?

Thanks,
Tammy

tammy,
apparently the appropriate replacement service can actually be found here.

its my understanding that even though the service requires an ArcGIS Online subscription (which is now included with the purchase of ArcGIS Desktop automatically) it doesn't actually burn credits.

as a developer, what this means to you is that you'll have to authenticate on behalf of end users to access the content if you don't want anyone to have to sign in. this would entail setting up our new resource-proxy and either registering your app or storing hardcoded user credentials and routing traffic to the elevation service through your proxy.

this is similar to what you'd do if you were interested in using other Esri services like traffic, batch geocoding or routing.

Re: Best way to get data from World Topo Map service

JohnGravois — Wed, 26 Feb 2014 19:55:40 GMT

actually, it looks like the identifyParameters for that image service are a fair amount different than what we see for map services.

i took the time to write up a sample which uses esriRequest to gather the info you're looking for. you'll have to sign in when running it in jsfiddle, but the same code could utilize a proxy on your own web server.

let me know if i can be of any more help.

Re: Best way to get data from World Topo Map service

TammyBearly — Wed, 26 Feb 2014 23:03:18 GMT

Thanks that looks like just what I need!

actually, it looks like the identifyParameters for that image service are a fair amount different than what we see for map services.

i took the time to write up a sample which uses esriRequest to gather the info you're looking for. you'll have to sign in when running it in jsfiddle, but the same code could utilize a proxy on your own web server.

let me know if i can be of any more help.