Calculate coordinates of Polyline in ArcGIS online with Arcade

DerrickPower

How can you calculate the start and stop coordinates of a polyline in ArcGIS online using Arcade?

With points you can use the following expression.

var CoorX = Round(geometry($feature).x, 6);

var originShift = 2.0 * PI * 6378137.0 / 2.0;
var lon = (CoorX / originShift) * 180.0;
// var lat = (y / originShift) * 180.0;

// lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
return lon;

What is a comparable expression to use for a polyline feature? I am just trying to get the coordinates at the start and end of the polyline. I don't need any points in between.

Thanks in advance.

XanderBakker

When you retrieve your polyline geometry, it will have a property "paths". This provides access to the coordinates of your polyline as describes here: https://developers.arcgis.com/arcade/guide/types/#polyline. 

This mentions the way the paths are constructed:

A three-dimensional array of numbers. The inner-most array contains the x,y,z,m coordinates of a single point. The second dimension contains additional points making up a line segment. The third dimension allows the polyline to have multiple segments.

To get to the first and last point you simply can do this (in this case "line" is the line geometry), like in Geometry($feature)

<SPAN class="keyword token">var</SPAN> paths <SPAN class="operator token">=</SPAN> line<SPAN class="punctuation token">.</SPAN>paths<SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> first_point <SPAN class="operator token">=</SPAN> paths<SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> last_point <SPAN class="operator token">=</SPAN> paths<SPAN class="punctuation token">[</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="token function">Count</SPAN><SPAN class="punctuation token">(</SPAN>paths<SPAN class="punctuation token">[</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="operator token">-</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">return</SPAN> first_point<SPAN class="punctuation token">.</SPAN>x <SPAN class="operator token">+</SPAN> <SPAN class="string token">" - "</SPAN> <SPAN class="operator token">+</SPAN> first_point<SPAN class="punctuation token">.</SPAN>y<SPAN class="punctuation token">;</SPAN>
<SPAN class="comment token">//return last_point.x + " - " + last_point.y;</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

Remember that your view scale will influence the precision of your result.

Be aware that using $feature as input to this function will yield results only as precise as the view's scale resolution. Therefore values returned from expressions using this function may change after zooming between scales.

See also: https://developers.arcgis.com/arcade/function-reference/geometry_functions/