topic Re: How to get Legend Info from web map services in ArcGIS JavaScript Maps SDK Questions

How to get Legend Info from web map services

DavidZhong2 — Fri, 17 Feb 2017 14:59:43 GMT

I am creating a custom TOC which needs to have both layer toggle and legend item (image data) for the web map. But the web map service does not have Legend Info. Does anybody know how to get legend info from the web map services. Any help would be very appreciated.

Re: How to get Legend Info from web map services

ChrisSmith7 — Fri, 17 Feb 2017 15:05:57 GMT

If you have created a legend, it should be available right on the map service, something like:

https://raster.nationalmap.gov/arcgis/rest/services/SampleWorldCities/MapServer/legend?f=pjson

You can also create the legend using something like:

Legend | ArcGIS API for JavaScript 3.19

Re: How to get Legend Info from web map services

JordanBaumgardner — Sun, 12 Dec 2021 16:06:51 GMT

You may find this useful once you get your JSON back from the legend url. [Ripped off from the old 3.x\digit]

/// Key Line

/// src = "data:image/png;base64," +
this.rootLayerTOC._legendResponse.layers[this.rootLayer.layerId].legend[0].imageData;
///

_getLegendIconUrl: function(legend) {
 var src = legend.url;
 if (src == null) {
 src = "data:image/png;base64," +
 this.rootLayerTOC._legendResponse.layers[this.rootLayer.layerId].legend[0].imageData;
 } else if (src != null && src.indexOf('data') == -1) {
 // in some cases NULL value may cause #legend != #of renderer entry.
 if (!has('ie') && legend.imageData && legend.imageData.length > 0) {
 src = "data:image/png;base64," + legend.imageData;
 } else {
 if (src.indexOf('http') !== 0) {
 // resolve relative url
 src = this.rootLayer.url + '/' + this.serviceLayer.id + '/images/' + src;
 }
 if (this.rootLayer.credential && this.rootLayer.credential.token) {
 src = src + "?token=" + this.rootLayer.credential.token;
 } else if (esriConfig.defaults.io.alwaysUseProxy) {
 src = esriConfig.defaults.io.proxyUrl + "?" + src;
 }
 }
 }
 return src;

Re: How to get Legend Info from web map services

DavidZhong2 — Fri, 17 Feb 2017 20:19:32 GMT

Thanks Jordan for the information. But the service I have is a WebMap service which does not have Legend Info JSON. The following is the screenshot of the service. You can see it only has ALL Layers and Tables link, no Legend link

Re: How to get Legend Info from web map services

DavidZhong2 — Fri, 17 Feb 2017 21:07:13 GMT

Thanks Chris for the response. The service I have does not have legend Info. Please see following screenshot. I am creating a TOC having both layers toggles and legend image. I was able to create a one for the map service having the Legend Info. But for the ArcGIS Online Map, I couldn't find a way to get the Legend Info.

Re: How to get Legend Info from web map services

FC_Basson — Mon, 20 Feb 2017 06:11:13 GMT

It's a Feature Service, that's why you are not seeing the legend option, but if you view the properties of each layer you should see the default render in the Drawing Info. You can also see it in the JSON of each layer.

Re: How to get Legend Info from web map services

JasonRainwater — Mon, 20 Feb 2017 20:04:44 GMT

Hi I work with david trying to figure this out. For ArcGIS server maps we are querying the legend information and populating a custom widget with the image data that is returned.

We are looking for something similar for webmaps. I know the renderer is there but how do you just dynamically create something that renders the renderer? First attempts required knowledge and specific code for all possible renderer types.

Do you know of a way to write one set of code that does not require switches based on every possible renderer type?

Re: How to get Legend Info from web map services

JordanBaumgardner — Mon, 20 Feb 2017 20:46:57 GMT

I think you simply need to RegEx your URL before sending, replacing FeatureServer with MapServer. Each Feature service will (must) have a matching MapServer.

But - to use your renderer... The 3.x util had a method that would return an SVG suitable for inserting into the browser dom. I was about to port when I realized I could hit the MapServer and get the same results, so I never pursued it. It ran through the JSON and created the image with js. Kinda brute force.

Re: How to get Legend Info from web map services

JasonRainwater — Mon, 20 Feb 2017 20:51:24 GMT

I should clarify that we are on the 4.x sdk currently on 4.2. Do you know of anything in there that can help?

From what I understand a webmap (or portal map) doesn't have a "map server". The webmap is like a wrapper around feature layers but it in itself is not a map server so I don't think we can get the same info as we do in a normal map server.

Re: How to get Legend Info from web map services

JordanBaumgardner — Mon, 20 Feb 2017 20:59:42 GMT

Well, that's kinda the crux of the issue. They have not ported it yet.

Re: How to get Legend Info from web map services

JordanBaumgardner — Mon, 20 Feb 2017 21:00:42 GMT

Oh - Right. But once the map layers loads, you run through it's collection and pull the SRC url from that. Swap out the FeaturServer for MapServer and your good to make your call.

Re: How to get Legend Info from web map services

JordanBaumgardner — Mon, 20 Feb 2017 21:06:20 GMT

Sorry, let me be more clear.

Load your WebMap as usual but listen for the LoadComplete (don't quote me on that exact event name), then run through the Map objects Layer list. Each one will have a source. You can then use that to complete your TOC.

Re: How to get Legend Info from web map services

JordanBaumgardner — Mon, 20 Feb 2017 21:08:06 GMT

A WebMap/Portal Map is just a wrapper around "Normal" esri services. Once it loads the Map object will have the actual services that the WebMap is made up of.

Re: How to get Legend Info from web map services

JasonRainwater — Mon, 20 Feb 2017 21:09:58 GMT

Ok gotcha, so there are urls that are used and populated that might not be visible by clicking around the webmap viewer. I tried digging through there to find what endpoints are available but couldn't find any that surfaced a "map server"

Re: How to get Legend Info from web map services

SethPatrich2 — Mon, 20 Feb 2017 21:46:00 GMT

Is it best to use the source from the Layer List? If the person who created that web map has made changes to the symbology in the web map, they would not show up in the actual feature service.

Re: How to get Legend Info from web map services

JordanBaumgardner — Wed, 22 Feb 2017 17:58:32 GMT

Yes, there are some key URL that everyone just kinda knows.

Try looking in YourServer\arcgis\rest\services <- that should be the base url to your services.

YourServer:6080\arcgis\manager

YourServer:6080\arcgis\admin

are also useful.

Re: How to get Legend Info from web map services

JasonRainwater — Thu, 23 Feb 2017 12:36:58 GMT

So I tried this. let me know if this is what you were talking about.

I have https://services.arcgis.com/somekey/arcgis/rest/services/myname/FeatureServer/0

I tried changing to https://services.arcgis.com/somekey/arcgis/rest/services/myname/MapServer/0

I get invalid url. Or is the url in the src after the layer loads different than this?

Re: How to get Legend Info from web map services

JordanBaumgardner — Thu, 23 Feb 2017 14:28:16 GMT

I would have expected that to work. It worked on my servers.

Try dropping the layer ID

/services.arcgis.com/somekey/arcgis/rest/services/myname/MapServer

/services.arcgis.com/somekey/arcgis/rest/services/myname/MapServer?f=json

will return the info in a code readable format.

/services.arcgis.com/somekey/arcgis/rest/services/myname//MapServer/legend or /MapServer/legend?f=json

should get you what you are after

Common esri rest params

f= Return Format [HTML | JSON | PJSON | more I can't remember ]

token= for secure services - go to "generate token" and add to your calls

Re: How to get Legend Info from web map services

JordanBaumgardner — Thu, 23 Feb 2017 14:36:07 GMT

Oh, and Yes. The URL that loads could be different from the container document (the portal/web map). It is a collection of regular map services. So the Web Map url might be different from its contents.

I'm getting nervous that I sound more authoritative than I feel. The Portal stuff is still pretty new to me.

But I do know that once a layer is loaded, there is a proper URL to it's no kidding source.

Re: How to get Legend Info from web map services

JasonRainwater — Thu, 23 Feb 2017 14:42:00 GMT

I tried https://services.arcgis.com/thekey/arcgis/rest/services/myname/MapServer and I'm still getting invalid url. but these are urls I'm pulling through digging down into the info of the webmap. I'm going to debug and pull some real resolved urls out and test them