Hello, I figured something out with a javascript. If this solution is an answer somewhere else, let me know.
In Survey123, it's not directly possible to calculate the centroid of a polygon drawn using a GeoShape question. However, there is a way to get an approximate centroid by using a custom JavaScript approach. Here's the solution I implemented:
1. Using a Custom JavaScript File:
- A JavaScript file is used to extract the coordinates of the polygon (in GeoJSON format) and calculate the centroid by averaging the X (longitude) and Y (latitude) coordinates of the points that make up the polygon.
The centroid.js file contains two separate functions:
- getCentroidX: to calculate the X (longitude) coordinate of the centroid.
- getCentroidY: to calculate the Y (latitude) coordinate of the centroid.
Here’s the JavaScript code used to calculate the centroid:
// Function to extract coordinates from a GeoJSON geometry
function extractCoordinates(geometry) {
if (geometry && geometry.rings && geometry.rings.length > 0) {
return geometry.rings[0].map(function(point) {
return [point[0], point[1]]; // Extracting only longitude (X) and latitude (Y)
});
}
return [];
}
// Function to calculate the Centroid X (longitude)
function getCentroidX(geometry) {
let coordinates = extractCoordinates(geometry);
let sumX = coordinates.reduce(function(sum, coord) { return sum + coord[0]; }, 0);
return sumX / coordinates.length; // Average of the X coordinates
}
// Function to calculate the Centroid Y (latitude)
function getCentroidY(geometry) {
let coordinates = extractCoordinates(geometry);
let sumY = coordinates.reduce(function(sum, coord) { return sum + coord[1]; }, 0);
return sumY / coordinates.length; // Average of the Y coordinates
}
2. Configuring the Form in Survey123:
- GeoShape: Allows the user to draw a polygon.
- poly_wkt: Stores the geometry as a WKT string (use string(${polygon}) to convert the GeoShape into a string).
- centroid_x and centroid_y: These fields calculate the X and Y coordinates of the centroid using pulldata() to call the JavaScript file. The pulldata() function is used as follows:
- number(pulldata("@javascript", "centroid.js", "getCentroidX", ${polygon}))
- number(pulldata("@javascript", "centroid.js", "getCentroidY", ${polygon}))
3. Creating a GeoPoint in a Repeat:
-To store the centroid geometry in a spatial layer, I used a GeoPoint inside a repeat.
-I used concat(${centroid_y}, ' ', ${centroid_x}) to combine the centroid coordinates and create a GeoPoint geometry in the form.
-This allows storing the centroid as a GeoPoint in the map layer with the calculated coordinates.
-Don't forget to add calculationMode=always in bind::esri:parameters
Here’s a quick look at the table structure in Excel:
