topic Re: How to create a Polygon from a single point in Geoprocessing Questions

How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 19:58:09 GMT

I'm trying to programmatically figure out how to create a polygon feature using just a single point. If my spatial reference is Web Mercator WGS84 and I want a 1 Meter by 2 Meter Polygon, how can I go about this? The point can be any Latitude Longitude, I just need to get an idea if this can be done or not. Thanks

Re: How to create a Polygon from a single point

DanPatterson_Retired — Mon, 18 Aug 2014 20:05:23 GMT

Why not use a projected coordinate system? What is the orientation of the rectangle that you need? Why is a rectangle needed and not a circle (ie a buffer)? Is this a grid pattern that you are trying to produce (ie Fishnet) over an area or for discrete points? Any further criteria would be useful

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 20:14:01 GMT

Hi Dan, A Projected Coordinate system is fine if thats easier. I'm actually working with State Plane Nad 83 Arkansas North Feet. It needs to be rectangular, otherwise I could do this by manipulating the point symbology. The angles of each corner can be 90 degrees but for simplicity purposes the rectangle dimensions can be 10 Feet by 20 Feet if projected then. Thoughts?

Re: How to create a Polygon from a single point

DanPatterson_Retired — Mon, 18 Aug 2014 20:21:59 GMT

If this is purely a symbology issue, I certainly wouldn't go to the trouble of trying to create rectangular features. There are some links in the help files on symbols and creating symbols

General comments

Creating your own

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 20:43:50 GMT

Hi Dan. A symbol will probably not work because I have to assume the user can zoom in at any level they choose to. I'm actually trying to create a graphic (polygon graphic with corners) in silverlight but I wanted to prove this up in Desktop first. So is this not possible at all? If its too difficult to produce a polygon could a line be derived?

Re: How to create a Polygon from a single point

DarrenWiens2 — Mon, 18 Aug 2014 20:44:16 GMT

If you really want to get into it, I believe you're looking for "Writing Geometries" using Python, but as Dan indicates this is likely overkill, especially if you are not proficient in Python.

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 20:51:00 GMT

Hi Darren, those examples look like a coordinates have to passed in though. Is there not a way to calculate where the 4 corners could be from the specfied point? I realize that the graphic or feature wd display in different orientations but if I producgraphic from this, it would at least have the correct dimensions and my template has the ability to rotate graphics.

Re: How to create a Polygon from a single point

DanPatterson_Retired — Mon, 18 Aug 2014 20:57:23 GMT

If you know the coordinates of the center of the feature, you can calculate the coordinates of four corners using simple math given you know the width and height of the feature you want to create...however, this would have to be done for each feature and they would not be scaleable as you zoom in and out. So the question becomes, how important is the actual size whether it be a feature or simply a symbol?

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 21:09:58 GMT

Hi Dan, yes could you give me an example of this? So in-essence, whenever a user clicks the map and has this process active, what would this calculation look like knowing the XY from the mouse click? It is important that the size of the new polygon feature matches the map (size = 10 Feet by 20 Feet). Thoughts?

Re: How to create a Polygon from a single point

DarrenWiens2 — Mon, 18 Aug 2014 21:13:32 GMT

West coordinate = KnownX - 0.5*width

East coordinate = KnownX + 0.5*width

North coordinate = KnownY + 0.5*height

South coordinate = KnownY - 0.5*height

Re: How to create a Polygon from a single point

DanPatterson_Retired — Mon, 18 Aug 2014 21:31:42 GMT

Okay...now you are describing a whole different problem. What you really want is to be able to click anywhere on the screen and have a rectangle appear...well at this stage it would be best for the ArcObjects people to wade in with coding ideas for "on mouse click" event style stuff. There is a world of difference between the static and the dynamic world...good luck

Re: How to create a Polygon from a single point

FilipKrál — Mon, 18 Aug 2014 23:14:32 GMT

Hi Joshua,

I'd say creating a polygon from a map click is certainly possible, but technicalities may be a bit different in ArcMap and the APIs.

When a user clickes a map, the map emits an on-click event. One of the properties of the parameter passed into the event handler is the point that was clicked. Take that point and calculate where the vertices of your polygon (like Darren suggested). I believe a map SilverLight (similarly to JavaScript) has one (or more) graphics layer(s), ideal for storing and displaying temporary geometries. Once you have your polygon, add it to the graphics layer.

Paste the code below into ArcGIS API for JavaScript Sandbox‌ . Is it roughly what you want to do?

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no"/>
    <title>Polygon from map click</title>
    <link rel="stylesheet" href="http://js.arcgis.com/3.10/js/esri/css/esri.css">
    <style>
      html, body, #map { height: 100%; width: 100%; margin: 0; padding: 0; }
      body { background-color: #FFF; overflow: hidden; font-family: "Trebuchet MS"; }
      #help {position: absolute; top: 20px; right: 20px; z-index: 1001; background-color: white; padding: 10px;}
    </style>
    <script src="http://js.arcgis.com/3.10/"></script>
    <script>
      var map;
     
      require(["esri/map", "esri/graphic",
        "esri/geometry/webMercatorUtils",
        "esri/geometry/Polygon",
        "esri/symbols/SimpleFillSymbol",
        "dojo/on","dojo/domReady!"
      ], function(Map, Graphic, webMercatorUtils, Polygon, SimpleFillSymbol) {
       
        map = new Map("map", { basemap: "topo",center: [-92.0, 35.0], zoom: 9 });
       
        var symbol = new SimpleFillSymbol({
          "type": "esriSFS", "style": "esriSFSSolid", "color": [255,0,0,100],
          "outline": {"type": "esriSLS", "style": "esriSLSSolid", "color": [255,0,0,255],"width": 1}
        });
       
        map.on('click', function(evt){
          var pt = evt.mapPoint;
          var x = pt.x, y = pt.y;
          var dx = 500, dy = 1000; // THESE ARE JUST WEB MERKATOR UNITS NOW, NOT METRES!!!
         
          var polygon = new Polygon({"rings":[[
              [x - dx, y - dy], [x - dx, y + dy],
              [x + dx, y + dy], [x + dx, y - dy], [x - dx, y - dy]
            ]], "spatialReference": pt.spatialReference});
         
          //var pgwgs = webMercatorUtils.webMercatorToGeographic(polygon); // might come handy
         
          var gr = new Graphic(polygon, symbol);
         
          map.graphics.clear(); // may need to remove just a particular graphic
          map.graphics.add(gr);
         
        });
       
      });
    </script>
  </head>

  <body>
    <div id="help">Click on the map to create a polygon</div>
    <div id="map"></div>
  </body>
</html>

I won't get into details about handling different coordinate systems now, maybe when we know what you are after. Also, you could potentially buffer the point and get envelope of the buffer to get a rectangle which you could then adjust. At what scale are you working? When I set the size to 10x20, the polygon wasn't even visible unless I zoomed really close.

Filip.

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 23:28:08 GMT

Thanks Darren, I'll try this tomorrow morning

Re: How to create a Polygon from a single point

JoshV — Mon, 18 Aug 2014 23:31:22 GMT

Hi Filip, thanks for this. while your code is more detailed and looks like what I'm after, I'm going to attempt Darren's code above tomorrow morning. If I can't get that to work, I'll try yours next before accepting an answer. Thanks for fast reply

Re: How to create a Polygon from a single point

OwenEarley — Tue, 19 Aug 2014 05:31:35 GMT

So in-essence, whenever a user clicks the map and has this process active, what would this calculation look like knowing the XY from the mouse click? It is important that the size of the new polygon feature matches the map (size = 10 Feet by 20 Feet). Thoughts?

You can do this using a python script in a custom toolbox.

import arcpy

# Get input parameters - points and target feature class
pts = arcpy.GetParameter(0)
dw = float(arcpy.GetParameterAsText(1))/2
dh = float(arcpy.GetParameterAsText(2))/2
units = arcpy.GetParameterAsText(3)
fc = arcpy.GetParameterAsText(4)

if units == "Feet":
    dw = dw/3.2808399
    dh = dh/3.2808399

# create new polygons from points
cursor = arcpy.da.InsertCursor(fc, ("SHAPE@"))
with arcpy.da.SearchCursor(pts,["SHAPE@XY"]) as newpts:
    for pt in newpts:
        x, y = pt[0]
        # Create polygon geometry from point       
        array = arcpy.Array([arcpy.Point(x - dw, y + dh),
                arcpy.Point(x + dw, y + dh),
                arcpy.Point(x + dw, y - dh),
                arcpy.Point(x - dw, y - dh),
                arcpy.Point(x - dw, y + dh)])
        poly = arcpy.Polygon(array)
        cursor.insertRow((poly,))

del cursor

The script takes the following inputs:

User Defined Points (Feature Set)
Width (size in units)
Height (size in units)
Units (Meters or Feet)
Target Feature Class (new polygons are created in this)

See this zipped example with toolbox, script and template point feature class (required for feature set parameter).

Note that this example uses the WGS 1984 Web Mercator (auxiliary sphere) projection – so you should use this in your target feature class as well.

Owen

Spatial XP

Re: How to create a Polygon from a single point

OwenEarley — Tue, 19 Aug 2014 05:38:00 GMT

Forgot to add - this is how it looks in ArcMap:

Re: How to create a Polygon from a single point

JoshV — Tue, 19 Aug 2014 12:50:20 GMT

Thanks Owen, this is indeed good to know. I may be able to push your script into a geoprocessing service if I can't get Darren's or Filip's code to work like I need it to. I will follow up, thanks

Re: How to create a Polygon from a single point

JoshV — Thu, 21 Aug 2014 13:07:43 GMT

Darren, thanks for this. There were a lot of great answers below but this turned out to be what I needed. Thanks

Re: How to create a Polygon from a single point

MattSheehan — Thu, 21 Aug 2014 22:42:22 GMT

Thanks for all the feedback here. Helped us solve a related problem.

Re: How to create a Polygon from a single point

OttoArturo — Sat, 25 Feb 2017 00:32:25 GMT

Filip, thank you for this. I am newbie with Arcgis for Javascript. What if I need to draw a polygon with exact height and width values? I cant find a way to do it. Any suggestion? thanks.

Damaso