topic Re: How can I get x,y in dec degrees from a poly feat serv using arcade? in Developers Questions

How can I get x,y in dec degrees from a poly feat serv using arcade?

GusMonteverde1 — Mon, 18 Dec 2017 23:37:54 GMT

Greetings Dev Community-

I need help with an arcade expression. I am trying to generate x,y pairs from a tax lot polygon feature service. In my "custom" field I have used the following expression:

var pnt= Centroid(Geometry($feature));
return Text(pnt);

RESULT...

{"x":-13649119.198784793,"y":5696311.278630899,"spatialReference":{"latestWkid":3857,"wkid":102100}}

but, I need the x and y to be returned in dec degrees, and my results appear to be on UTM northing/easting

I also tried to call a member method X and Y but I am getting the following error...

Thanks!

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Fri, 10 Dec 2021 22:48:19 GMT

Try this:

Expression:

var poly = Geometry($feature);

var result = "";
if (!IsEmpty(poly)) {
    var pnt_centr = Centroid(poly);
    Console(pnt_centr);
    result = "(" + Round(pnt_centr.X, 2) + ", " + Round(pnt_centr.Y, 2) + ")";
}

return result‍‍‍‍‍‍‍‍‍‍

Returns this result:

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

GusMonteverde1 — Tue, 19 Dec 2017 15:45:43 GMT

That worked, and gets me half the way there. I still need those coords formatted to decimal degrees. Is that possible to do using Arcade? I much appreciate all your help so far.

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Tue, 19 Dec 2017 15:52:44 GMT

If you have projected coordinates you cannot currently translate (project) those to geographic coordinates. That might come in the features when more geometric functions will be implemented.

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

GusMonteverde1 — Tue, 19 Dec 2017 17:21:18 GMT

Understood. Thanks again!

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Wed, 21 Mar 2018 13:49:02 GMT

Hey Xander!

Is there a way to change the projection from one projected coordinate system to another in arcade?

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Fri, 10 Dec 2021 22:48:23 GMT

Just this morning I did a test to see f I could create a URL that initiates Waze in navigation mode. In Colombia only historic traffic is available in Navigator, and our client needed real time traffic info.

To make this work the coordinates need to be provided in lat lon. At the DevSummit this month there was an announcement that the JavaScript API would will include the projection engine to do client side projections, which is very cool and fast. Not sure if we will be able to take advantage of this in the update next month (April 10th).

To be able to advance and provide some solution for this client I came up with the following expression:

function MetersToLatLon(mx, my) {
    // Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum
    // source: http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/
    var originShift = 2.0 * PI * 6378137.0 / 2.0;

    var lon = (mx / originShift) * 180.0;
    var lat = (my / originShift) * 180.0;

    lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
    return [lat, lon];
}

function CreateWazeURL(lat, lon) {
    return "https://waze.com/ul?ll=" + lat + "," + lon + "&navigate=yes"
}

var latlon = MetersToLatLon(Geometry($feature).X, Geometry($feature).Y);
var url = CreateWazeURL(latlon[0], latlon[1]);
return url;‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

I did some testing with a web map on my iPad and it works like a charm. This only convert the Web Mercator Auxiliary Sphere coordinates to WGS1984 decimal degrees.

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Fri, 10 Dec 2021 22:48:25 GMT

CC Gus Monteverde , I think this could solve your problem too related to obtaining the coordinate as decimal degrees:

function MetersToLatLon(mx, my) {
    // Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum
     // Fuente: http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/
    var originShift = 2.0 * PI * 6378137.0 / 2.0;

    var lon = (mx / originShift) * 180.0;
    var lat = (my / originShift) * 180.0;

    lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
    return [lat, lon];
}


var poly = Geometry($feature);

var result = "";
if (!IsEmpty(poly)) {
    var pnt_centr = Centroid(poly);
    Console(pnt_centr);

     var latlon = MetersToLatLon(pnt_centr[0], pnt_centr[1]);

    result = "(" + Round(latlon[0], 6) + ", " + Round(latlon[1], 6) + ")";
}

return result‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Mon, 16 Apr 2018 18:13:51 GMT

Awesome example -- do you know how I would go about finding the mathematics to convert 2857 (Web Mercator Auxiliary Sphere) to 2264 (NC State Plane). I've been looking for the equations for the transformation and haven't had any luck

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Mon, 16 Apr 2018 18:33:54 GMT

Sorry, I don't know that, but perhaps Melita Kennedy can help, since she is an expert in this field.

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

MelitaKennedy — Mon, 16 Apr 2018 20:18:07 GMT

Unfortunately, I know nothing about Arcade except that it's an expression language. I just looked through our Arcade website and some references to Arcade on the Javascript API pages. It doesn't look like the functions/methods are there to take apart a feature or even to change the coordinate system/projection engine.

Does the feature service support only 2264?

2264, NAD83 NC State Plane (US survey feet), uses Lambert conformal conic (LCC) with these parameters:

False Easting:2000000.002616666 (odd number due to being converted from a truncated value in meters)
False Northing:0.0
Central Meridian:-79.0
Standard Parallel 1:34.33333333333333
Standard Parallel 2:36.16666666666667
Latitude of Origin:33.75

It's on the GRS80 ellipsoid:

semimajor axis: 6378137.0

flattening: 1.0/298.257222101

LCC is not an easy projection to implement. You need the ellipsoidal version of the equations. One place to find them is John P. Snyder's Map Projections: A Working Manual, available in PDF form from this USGS site: Map projections: A working manual

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Mon, 16 Apr 2018 20:21:42 GMT

Thanks for your feedback -- unfortunately our data is stored in 2264, so when I try to pass coordinate values through to a C# application that executes spatial SQL queries it fails as you can't use two different projections when executing native SQL spatial

Alas, I'll keep looking for a solution!

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Mon, 16 Apr 2018 20:31:48 GMT

Thanks for sharing Melita Kennedy , indeed that sounds pretty complex. Great resource you shared (I only I had the time to read those ±400 pages).

96213@charlottenc.gov_charlotte , wouldn't you be able to use PROJ — PROJ.4 5.0.0 documentation in C#: Coordinate Transformation Using Proj4 in .NET - CodeProject ?

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Wed, 02 May 2018 07:13:19 GMT

Hi Xander Bakker‌ - this is terrific, however I get this error when Testing in Arcade Expression builder:

Execution Error:Runtime Error: Cannot call member property on object of this type.

- I've simply cut/pasted your code above, using on a polygon feat serv.

Any ideas why I'd get that message?

Thanks!

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Wed, 02 May 2018 11:29:36 GMT

That's strange... Do you have multipart geometry? What coordinate system is your data using?

Is the service shared publicly? If so, can you share the URL so i can test against it?

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Thu, 03 May 2018 01:55:22 GMT

Thanks Xander Bakker‌

It was multipart, but I've corrected that, and still get that same error.

This is a public view of the data:
https://services6.arcgis.com/CubtY3H3UowKJNc4/arcgis/rest/services/Buildings_and_Structures_2_1/FeatureServer

And when I try on another simpler (public) polygon feat serv, I get the same error also.

https://services6.arcgis.com/CubtY3H3UowKJNc4/arcgis/rest/services/Fire_History/FeatureServer

Perhaps I am doing something wrong? I am simply opening up the Attribute Expression builder and pasting in the code above (below), and hitting 'Test'

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Fri, 10 Dec 2021 22:48:28 GMT

You didn't do anything wrong. I guess something changed in Arcade with the way you can access the X and Y properties of the point. It is necessary to use pnt_centr.x, pnt_centr.y instead of pnt_centr[0], pnt_centr[1] (see line 20):

function MetersToLatLon(mx, my) {
    // Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum
     // Fuente: http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/
    var originShift = 2.0 * PI * 6378137.0 / 2.0;

    var lon = (mx / originShift) * 180.0;
    var lat = (my / originShift) * 180.0;

    lat = 180.0 / PI * (2.0 * Atan( Exp( lat * PI / 180.0)) - PI / 2.0);
    return [lat, lon];
}


var poly = Geometry($feature);

var result = "";
if (!IsEmpty(poly)) {
    var pnt_centr = Centroid(poly);

    var latlon = MetersToLatLon(pnt_centr.x, pnt_centr.y);

    result = "(" + Round(latlon[0], 6) + ", " + Round(latlon[1], 6) + ")";
} else {
    result = "";
}

return result;‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Result:

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Fri, 04 May 2018 02:21:17 GMT

Many many thanks to you Xander Bakker‌ - you are generous with your time, and saved me a lot of it! I've been trying to find more information about the Arcade language to dig into the issue, and could only find the documentation at ArcGIS Arcade | ArcGIS for Developers - which is relatively simple and didn't get into that detail.
Can I ask how you found out what the issue was?

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

XanderBakker — Fri, 04 May 2018 13:53:07 GMT

You 're welcome and I'm glad that it is working now.

The site you are referencing is the source documentation for Arcade. There are however a number of blog posts and threads that have relevant information and explain in more detail how to accomplish something. You could have a log here:

https://community.esri.com/content?filterID=all~objecttype~objecttype%5Bblogpost%5D&query=arcade

Especially the blog by Kelly Gerrow‌: https://community.esri.com/community/gis/web-gis/arcgisonline/blog/2017/07/18/conditional-field-display-with-arcade-in-pop-ups is a good read.

I have published a number of documents related to Arcade (but most are in Spanish, although you might find it helpful):

/people/xander_bakker/content?query=arcade

To find the issue the error message "cannot calling a member property" was an important clue. Since no line number is returned I have to include some Console statements like:

Console("pnt_centr:" + pnt_centr);‍

... after line 19 to see what the value of the variable is and if it is valid.

Once I knew the line where the error was occurring, I tried reading the X and Y properties differently. The old way used to work, but it seems that something has changed along the line (perhaps at the AGOL update last month, although Arcade remained at version 1.3.0 December 2017).

Re: How can I get x,y in dec degrees from a poly feat serv using arcade?

Anonymous User — Mon, 07 May 2018 00:58:53 GMT

Thanks again, Xander Bakker‌ - good tips there! Thanks again for your time 🙂