I'm using Google Earth Engine (GEE) to calculate the Euclidean distance from sample points to the nearest brightest pixel above the threshold value "avg_rad > 10" in nighttime light data. Some of the point coordinates I use as the base shapefile are as below:

U   -14.335572  35.639824
U   -13.203245  37.501709
U   -15.198814  35.863956
R   -13.422739  34.870815
R   -13.203394  35.187214
R   -15.004614  36.633186
R   -14.895029  36.772968
R   -14.597268  36.350857
R   -14.488451  36.53352

My approach:

• Process VIIRS Data: Compute the median of 2021 data and mask bright pixels (avg_rad > 10).
• Compute Distance: Use fastDistanceTransform(1024).sqrt().
• Find Nearest Bright Pixel: Convert bright pixels to centroids with reduceToVectors(), then match them to sample points.
• Extract Distance: Sample distance_to_bright at sample points.

Am I coding it correctly?

// ==========================
// 1️⃣ Load & Process Nighttime Light Data (VIIRS)
// ==========================
var nightLights = ee.ImageCollection('NOAA/VIIRS/DNB/MONTHLY_V1/VCMSLCFG')
  .filterDate('2021-01-01', '2021-12-31')  // Use one year of data
  .median()  // Reduce noise by computing the median composite
  .select('avg_rad');  // Select the average radiance band
 
// ==========================
// 2️⃣ Compute Euclidean Distance to Nearest Bright Pixel (avg_rad > 10)
// ==========================
var brightPixels = nightLights.gt(10);  // Mask for bright pixels
 
// Compute Euclidean distance to the nearest bright pixel
var distToBright = brightPixels.fastDistanceTransform(1024).sqrt()
  .rename('distance_to_bright');
 
// ==========================
// 3️⃣ Define Sample Points
// ==========================
 
// Load sample points from shapefile
var samplePoints = ee.FeatureCollection("projects/ee-researchgamage/assets/base1");
 
// ==========================
// 4️⃣ Define Region and Extract Nearest Bright Pixel Coordinates
// ==========================
// Ensure processing is limited to the area where night lights exist
var nightLightsBounds = nightLights.geometry();
var region = nightLightsBounds.intersection(samplePoints.geometry().buffer(50000), ee.ErrorMargin(1));
 
var brightPixelPoints = brightPixels.selfMask()
  .reduceToVectors({
    geometryType: 'centroid',
    scale: 500,
    geometry: region,
    geometryInNativeProjection: false,
    maxPixels: 1e7,  // Set max pixels to 10 million
    bestEffort: true  // Allow flexible aggregation
  });
 
 
// Function to find nearest bright pixel for each sample point
var findNearestBrightPixel = function(feature) {
  var nearestBright = brightPixelPoints
    .filterBounds(feature.geometry())  // Search for nearby bright pixels
    .sort('distance_to_bright')  // Sort by distance
    .first();  // Get closest
 
  // Extract coordinates safely
  var brightLonLat = ee.Algorithms.If(
    nearestBright,
    ee.Feature(nearestBright).geometry().coordinates(),
    ee.List([null, null])  // Handle cases with no bright pixel nearby
  );
 
  // Set attributes
  return feature.set({
    'point_lon': feature.geometry().coordinates().get(0),
    'point_lat': feature.geometry().coordinates().get(1),
    'bright_lon': ee.List(brightLonLat).get(0),  // Extract longitude
    'bright_lat': ee.List(brightLonLat).get(1)   // Extract latitude
  });
};
 
// Apply function to sample points
var enrichedSamplePoints = samplePoints.map(findNearestBrightPixel);
 
// ==========================
// 5️⃣ Extract Distance for Sample Points
// ==========================
var sampledDistances = distToBright.sampleRegions({
  collection: enrichedSamplePoints,
  scale: 500,  // Adjust based on VIIRS resolution
  projection: 'EPSG:4326',
  geometries: true
});
 
// Print extracted distances
print("Sampled Distances:", sampledDistances);
 
// ==========================
// 6️⃣ Export CSV with Coordinates
// ==========================
Export.table.toDrive({ 
  collection: sampledDistances,
  description: 'Point_Distance_to_Bright_Night_Areas_2021',  // Naming it as 2020
  folder: 'GEE_Exports',
  fileNamePrefix: 'point_distance_2021',  // Forces the output name to 2020
  fileFormat: 'CSV'
});
//======================