topic Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features? in ArcGIS JavaScript Maps SDK Questions

Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Tue, 22 Aug 2017 19:43:50 GMT

I'll apologize upfront for the cross post - this has also been asked here. If cross posting is frowned upon I'll be happy to take this down.

I'm using a print widget to get exports of a map view. My view has a number of layers, one of them is a feature layer (in this case, showing US ZIP codes). When I look at the ExportWebMap specification it looks like the syntax for feature layers, I should be able to simply provide object IDs for the features that ought to be displayed in the export. However, when I look at the JSON that's sent to the export service's execute task I see that my feature layer was instead treated as a collection of client side graphics - with full geometries listed instead of object IDs.

Aside from being slow this also causes the export operation to crash when my request payload gets too large.

Any insight as to why my FeatureLayer features might be getting serialized as client side graphics?

I'm using version 4.4 of the ArcGIS API for JavaScript.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

RobertScheitlin__GISP — Tue, 22 Aug 2017 20:14:52 GMT

Justin,

This is the expected behavior and has been for a long time (even in the 3.x API).

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

ThomasSolow — Tue, 22 Aug 2017 20:30:38 GMT

My feeling is that the features are going to have to make their way to the print service one way or another in order to be converted to an image. Whether this is done by your client sending whatever feature data it has currently or the service making separate requests to the feature service based on the oids passed in, the result is going to be more or less the same.

It's surprising to me that this is causing issues. Are the features that get passed in filtered by the extent of the view? How many features are we talking about here?

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Tue, 22 Aug 2017 22:19:09 GMT

Thanks, Robert. To be perfectly honest, this is my first time using the print widget. Can you point to where this specific behavior is documented? I didn't seem to come across that mentioned anywhere. I don't doubt that I'm seeing intended behavior, but it does seem like a sub-optimal (though arguably more generic) use of the API so I'm wondering if there are hooks for either intercepting the built JSON or otherwise configuring what get's sent to the server. In my case I may need to find a workaround or else effectively rebuild the print widget from scratch...

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Tue, 22 Aug 2017 22:53:20 GMT

Hi Thomas, thanks for the response! It's a fair point about features needing to make their way to the print service either way. That said, coming from the client we're potentially talking about a lot to send over the wire. We also have much less control over network speeds, etc. I feel like you could support better (or just different) feature resolution with those geometries getting expanded on the server as opposed to just using what's on the client. But you're absolutely right, it's gotta happen somewhere.

It looks like I'm *mostly* seeing things being filtered by view extent with a bit of a buffer. This makes sense, depending on the dimensions of the export image vs the client side view you might need more or fewer features than reside within your view extent.

I copied the error from ArcServer logs below. The Web Map as JSON param is definitely present when the request leaves my browser. It could be getting truncated somewhere along the way - I'll need to do some digging there.

Error executing tool. Export Web Map Task : ERROR 000735: Web Map as JSON: Value is required The value is empty. The value is empty. ERROR 000735: Web Map as JSON: Value is required

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

RobertScheitlin__GISP — Tue, 22 Aug 2017 23:30:02 GMT

Justin,

As William most JS API internals there is no specific documentation on this. For those of use that have used the API for years now we are just familiar with this. You can as some have alter the json before it is sent using esriRequest.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Wed, 23 Aug 2017 02:36:33 GMT

Hi, Robert. I'm sorry, would you mind elaborating on that last comment? I see esriRequest but it looks like an AJAX helper utility. Is there a way to intercept requests made by the framework with this? Or are you suggesting I just redefine "esri/request".

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Wed, 23 Aug 2017 02:42:23 GMT

FYI I'm seeing request payloads of about ~20MB. This thread (Export Web Map Task - JSON length limit?) led me to check my own server configs and indeed I'm at the default of 10MB as a cap for POST sizes. I checked the other components of my stack and as far as I can see this is the only place I could be hitting a size limit.

Hopefully that provides a short term fix but figuring out how to bring this down to a reasonable number could still be interesting.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

RobertScheitlin__GISP — Wed, 23 Aug 2017 12:43:26 GMT

Justin,

I am not sure if this has been implemented for the 4.x API but here is a thread on how it is done in 3.x:

setRequestPreCallback on PrintTask

EDIT: If you look at that thread the very last post says it is implemented in 4.x just has not been documented yet.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

ThomasSolow — Wed, 23 Aug 2017 13:11:01 GMT

20 MB, wow. Just curious, how many features are being sent?

I think it's possible that you can send objectIds instead, as it says in the documentation, but (for whatever reason) sending whole features is preferred.

I haven't tried it, but you might be able to tap into your export requests before they're sent using the "setRequestPreCallback" (as Robert mentioned) and replace the features with objectIds before the request is sent. Another option would be to strip out attributes and other extraneous from the request. You may not need most attributes (depends on your renderer) or you may be able to delete the attribute property entirely.

I'll see if I can get a sample working to try out objectIds.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

ThomasSolow — Wed, 23 Aug 2017 14:04:42 GMT

Here's a sample that strips out each feature layer JSON from the request and replaces it with object ids filtered by the view's extent: JS Bin - Collaborative JavaScript Debugging

This doesn't seem to work from jsbin, but if you copy the html/js to here: ArcGIS API for JavaScript Sandbox and it works for me.

The specifics of this process might vary for you but the specification does appear to be correct, so you can pass in objectIds rather than entire features. For this example, the content length went from 169,698 to 11,319 and the image seems the same to me.

I don't know why the JS API sends entire features, but there may be a good reason for it (or not).

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Wed, 23 Aug 2017 15:15:07 GMT

Thanks, Thomas. The number of features being sent varies quite a bit but hovers around 100. The feature layer in question is plotting US ZIP Codes - so while there may not be many features, their geometries can be complex (the vast majority of the request payload is geometry rings). The layer is not set to display at high zoom levels.

Thanks for sharing the link below - that's super helpful. I'll experiment setRequestPreCallback as you demonstrated .

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Wed, 23 Aug 2017 15:19:44 GMT

It sounds like this is technically the correct answer for the question as asked. Though many thanks for TSolow-esristaff for super helpful info on getting me around the issue.

Re: Why does PrintWidget create Web_Map_as_JSON with explicit geometries for FeatureLayer features?

JustinRussell — Mon, 28 Aug 2017 20:26:58 GMT

Incidentally, I followed up with an Esri rep and confirmed this is the expected behavior.