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

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09-09-2020 05:21 AM
KaramKhattab2
New Contributor II

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 !! 

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XanderBakker
Esri Esteemed Contributor

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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9 Replies
XanderBakker
Esri Esteemed Contributor

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";
KaramKhattab2
New Contributor II

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!!!!!

XanderBakker
Esri Esteemed Contributor

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. 

KaramKhattab2
New Contributor II

Thank you so much for the clarification!!  

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DrewDowling
Occasional Contributor III

Are you a wizard?

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Bud
by
Regular Contributor II

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...

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Robertc13
New Contributor III

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.

Bud
by
Regular Contributor II

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/highl... 

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.

 

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Robertc13
New Contributor III

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