retrieving map extent across 180

WayneGuidry

I'm performing IDL (international date line) testing on an application and am having an issue getting the map extent if the map view crosses over 180 degrees. If I zoom in around the 180 longitude and then use the code below to get the current display extent:

Esri::ArcGIS::Runtime::ViewPoint mapViewPoint = m_mapView->currentViewPoint(Esri::ArcGISRuntime::ViewPointType::BoundingGeometry);

Esri::ArcGIS::Runtime::Envelope *m_pZoomBox = new ESRI::ArcGISRuntime::Envelope(Esri::ArcGISRuntime::GeometryEngine::project(mapViewPoint.targetGeometry().extent(), Esri::ArcGISRuntime::SpatialReference::wgs84()));

Checking the return envelope, results in the xMin being -180 and the xMax being 180 which doesn't help determine the boundary of the extent in view. It seems like there should be a way to convert it to a 0 to 360 reference so you can get the actual extent of the map.

Is there a different call I should make to get the bounds across 180? I'm using ArcGIS Runtime 100.1.

Thanks for any assistance!

Lucas Danzinger

I think the issue might be related to the Project call. In your example, what spatial reference is the Map in? My assumption is web mercator. If you use a wgs84 basemap instead and don't call project, it seems to properly give you xMin/Max beyond 180/-180. For example, here is some QML that gives me expected behavior

<SPAN class="comment token">// add a mapView component</SPAN>
MapView <SPAN class="punctuation token">{</SPAN>
&nbsp;&nbsp;&nbsp; id<SPAN class="punctuation token">:</SPAN> mapView
&nbsp;&nbsp;&nbsp; anchors<SPAN class="punctuation token">.</SPAN>fill<SPAN class="punctuation token">:</SPAN> parent

&nbsp;&nbsp;&nbsp; <SPAN class="comment token">// add a map to the mapview</SPAN>
&nbsp;&nbsp;&nbsp; Map <SPAN class="punctuation token">{</SPAN>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Basemap <SPAN class="punctuation token">{</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ArcGISTiledLayer <SPAN class="punctuation token">{</SPAN>
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Button <SPAN class="punctuation token">{</SPAN>
&nbsp;&nbsp;&nbsp; text<SPAN class="punctuation token">:</SPAN> <SPAN class="string token">"Get WGS84 Extent"</SPAN>
&nbsp;&nbsp;&nbsp; onClicked<SPAN class="punctuation token">:</SPAN> <SPAN class="punctuation token">{</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text<SPAN class="punctuation token">.</SPAN>text <SPAN class="operator token">=</SPAN> JSON<SPAN class="punctuation token">.</SPAN><SPAN class="token function">stringify</SPAN><SPAN class="punctuation token">(</SPAN>mapView<SPAN class="punctuation token">.</SPAN>currentViewpointExtent<SPAN class="punctuation token">.</SPAN>extent<SPAN class="punctuation token">.</SPAN>json<SPAN class="punctuation token">)</SPAN>
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I think it might be expected that the xMin/Max defaults to -180/180 when you call project because the coordinates you are passing in from the original geometry are outside the bounds of the spatial reference, and so once that gets processed in the project function, it just defaults.

With all of that said, if your end goal is the use web mercator and do a spatial query across the dateline, I think this is the general workflow you could follow:

- get the viewpoint extent Envelope

- don't project

- normalize the geometry to get folded geometry use normalizeCentralMeridian. 

- This will give you back a multipart polygon where 1 part is on the western side and one is on the eastern side of the dateline

- Pass that into your query parameters, as this should work with multipart geometries

For example, your query will perform against:

instead of