topic How to get the mid point (X,Y) of a polyline segment in Arcade ? in ArcGIS Online Questions

How to get the mid point (X,Y) of a polyline segment in Arcade ?

Anonymous User — Wed, 09 Sep 2020 12:21:47 GMT

Can someone please help me find out how to get the midpoint (x.y) of a line segment in Arcade (ArcGIS Online) ?

I have a road layer with many segmented lines, I want to create a pop up link using the mid point x,y info.

Thank you so much !!

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

XanderBakker — Sat, 11 Dec 2021 18:01:11 GMT

Hi KhattabK ,

Not entirely sure if this works, but could you try it?

Function dist(x1, y1, x2, y2) {
    return Sqrt(Pow(x2-x1, 2) + Pow(y2-y1, 2));
}

// get the geometry
var segment = Geometry($feature)["paths"][0];
// determine length halfway
var halflen = Length($feature) / 2;

// initialize vars
var xcrd = Null;
var ycrd = Null;
var cumlen = 0;

// loop through coordinate pairs in segment
for (var i in segment) {
    if (i > 0) {
        // second coordinate pair, start calculating distance
        var xprev = segment[i-1]["x"];
        var yprev = segment[i-1]["y"];
        var xcurr = segment[i]["x"];
        var ycurr = segment[i]["y"];
        var len = dist(xprev, yprev, xcurr, ycurr);
        var prevcum = cumlen;
        cumlen += len;
        // if past halfway on line
        if (cumlen > halflen) {
            // calculate midpoint
            var restlen = halflen - prevcum;
            var frac = restlen / len;
            var xmid = (xcurr - xprev) * frac + xprev;
            var ymid = (ycurr - yprev) * frac + yprev;
            return "(" + Round(xmid, 2) + ", " + Round(ymid, 2) + ")";
        }
    } else {
        // first coordinate pair
        var xcrd = segment[i]["x"];
        var ycrd = segment[i]["y"];
    }
}

return "Error";
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Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Anonymous User — Mon, 14 Sep 2020 15:52:20 GMT

Hi Xander Bakker !

Thank you so much for getting back to me so quickly ! I really appreciate your help.

This worked like a champ ! I had to add the Meters to Lat Long Function & concatenation to get what I wanted. I will share the source link here for the benefit. Lat/Long unit conversion with Arcade

I was wondering if you know if this is possible in Arcade :

The ability to grab the x,y of the user's mouse click and put it in Arcade for String Concatenation. (please see snip below)

Thank you so much Xander Bakker!!!!!

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

XanderBakker — Mon, 14 Sep 2020 19:26:39 GMT

Hi KhattabK ,

Unfortunately, it is not possible to access the exact location where the user clicked. It would be great to be able to do this. Currently for a pop-up you will have access (initially) to the feature geometry where the user clicked, but not the exact location. No problem for point data, but it will be for polylines and polygons.

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Anonymous User — Mon, 14 Sep 2020 19:32:39 GMT

Thank you so much for the clarification!!

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Bud — Mon, 28 Feb 2022 22:17:34 GMT

If for some reason that midpoint expression doesn't work, this might be an option:

Buffer the line and get the centroid of the resulting polygon. It's kind of like a "poor man's midpoint".

If I recall, that works ok. But I think I remember the point not being the exact midpoint of the line. I forget what the specific issue was. It's probably good enough for most use cases though...

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

DrewDowling — Thu, 16 Jun 2022 03:40:20 GMT

Are you a wizard?

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Anonymous User — Thu, 16 Jun 2022 14:46:36 GMT

In Desktop in Toolbox you can use the Data Management > Features > Add Geometry Attributes.

Add the line you're wanting to determine the midpoint for as the Input Feature and check the box next to Line_Start_Mid_End. This will add columns in the line's attribute table showing the coordinates for the Start X and Y, Mid X and Y, End X and Y in the same coordinate system as the line. It doesn't actually create a point but you could then create a feature using these coordinates.

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Bud — Thu, 16 Jun 2022 18:02:23 GMT

~~That's an interesting idea.~~

~~If I understand correctly, I think you're saying we could:~~

...reference those "Geometry Attributes" (fields in the attribute table but not in the underlying db table) right in Arcade. I think I've done the same sort of thing with the $feature.shape_length: https://community.esri.com/t5/arcgis-pro-ideas/hascurve-arcade-geometry-property/idc-p/1149449/highlight/true#M18873

~~Is that what you were thinking?~~

Never mind. Those "Geometry Attribute" fields aren't dynamic.

Add Geometry Attributes (Data Management)
The values in these fields are not automatically recalculated after edits. If you edit the features, you'll need to run this tool again to update the field values.

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

Anonymous User — Thu, 16 Jun 2022 20:34:47 GMT

I meant use that function to obtain the midpoint and then create a point (Editor > Create Feature with Absolute X, Y) in ArcMap.

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

BenjamanGarrett-FG — Fri, 04 Aug 2023 14:32:19 GMT

As I am a novice with Arcade, I am loving this post. Xander Bakker's post works great, but I am like you and need the Lat/Long. You have the code link for that, but I am not sure how to add it to the original function. Can you give me some advice as to where to insert it?

Thank You in advance!

Re: How to get the mid point (X,Y) of a polyline segment in Arcade ?

TanGnar — Tue, 14 Nov 2023 20:56:02 GMT

I want to add to the discussion (and possibly be corrected if I'm wrong). This gets the more precise midpoint of the feature, but doesn't always return a point on the line if the line is not straight. If you don't need a precise midpoint and you want the coordinates to be on the line, I've found the easier option is to get the number of a paths in the geometry object, and get coordinates from one of those paths closest to the middle. If there are 11 paths in the segment, get the 5 or 6th and use those coordinates. then it's always on the line, and the code is simpler.