export-utils.js•4.62 kB
const { getEarthEngine } = require('./init');
/**
* Generate both thumbnail and full-resolution export URLs
* @param {object} image - Earth Engine image object
* @param {object} params - Export parameters
* @returns {object} URLs and metadata
*/
function generateExportUrls(image, params) {
const ee = getEarthEngine();
const {
region,
scale = 10,
crs = 'EPSG:4326',
bands = null,
fileName = `export_${Date.now()}`,
maxPixels = 1e9,
thumbnailSize = '1024x1024'
} = params;
// Get band names
let exportBands = bands;
if (!exportBands) {
const bandNames = image.bandNames();
exportBands = bandNames.getInfo();
}
// Select bands for export
const exportImage = bands ? image.select(bands) : image;
// Generate thumbnail URL for preview (small, quick)
const thumbnailUrl = exportImage.getThumbURL({
dimensions: thumbnailSize,
region: region,
format: 'png',
min: 0,
max: 3000
});
// Generate download URL for full GeoTIFF (full resolution)
const fullDownloadUrl = exportImage.getDownloadURL({
name: fileName,
region: region,
scale: scale,
crs: crs,
format: 'GeoTIFF',
maxPixels: maxPixels,
filePerBand: false
});
// For very large exports, provide batch export instructions
const estimatedPixels = estimatePixelCount(region, scale);
const needsBatchExport = estimatedPixels > maxPixels;
return {
thumbnail: {
url: thumbnailUrl,
description: 'Quick preview image (PNG)',
dimensions: thumbnailSize
},
download: {
url: fullDownloadUrl,
description: 'Full resolution GeoTIFF download',
format: 'GeoTIFF',
scale: scale,
crs: crs,
bands: exportBands,
bandCount: exportBands.length
},
metadata: {
fileName: `${fileName}.tif`,
estimatedPixels: estimatedPixels,
needsBatchExport: needsBatchExport,
maxPixelsAllowed: maxPixels
},
batchExportNote: needsBatchExport ?
'This export is too large for direct download. Use Export.image.toDrive() for batch processing.' :
null
};
}
/**
* Estimate pixel count for an export
* @param {object} region - Export region
* @param {number} scale - Resolution in meters
* @returns {number} Estimated pixel count
*/
function estimatePixelCount(region, scale) {
// Rough estimation based on region type
if (!region) return 1e6; // Default estimate
if (region.type === 'Point') {
// Point with 5km buffer
const bufferArea = Math.PI * 5000 * 5000; // m²
return Math.ceil(bufferArea / (scale * scale));
} else if (region.type === 'Polygon' && region.coordinates) {
// Very rough estimate for polygon (assumes square-ish shape)
// This is a simplification; actual calculation would need geodesic area
const coords = region.coordinates[0];
if (coords && coords.length >= 3) {
const minLon = Math.min(...coords.map(c => c[0]));
const maxLon = Math.max(...coords.map(c => c[0]));
const minLat = Math.min(...coords.map(c => c[1]));
const maxLat = Math.max(...coords.map(c => c[1]));
// Convert degrees to meters (rough approximation at equator)
const width = (maxLon - minLon) * 111320;
const height = (maxLat - minLat) * 110540;
const area = width * height;
return Math.ceil(area / (scale * scale));
}
}
return 1e7; // Default for unknown
}
/**
* Create a batch export task to Google Drive
* @param {object} image - Earth Engine image
* @param {object} params - Export parameters
* @returns {object} Task information
*/
function createDriveExportTask(image, params) {
const ee = getEarthEngine();
const {
region,
scale = 10,
crs = 'EPSG:4326',
bands = null,
folder = 'EarthEngine',
description = `export_${Date.now()}`,
maxPixels = 1e10
} = params;
// Select bands if specified
const exportImage = bands ? image.select(bands) : image;
// Create the export task
const task = ee.batch.Export.image.toDrive({
image: exportImage,
description: description,
folder: folder,
fileNamePrefix: description,
region: region,
scale: scale,
crs: crs,
maxPixels: maxPixels,
fileFormat: 'GeoTIFF',
formatOptions: {
cloudOptimized: true // Create Cloud-Optimized GeoTIFF (COG)
}
});
return {
task: task,
description: description,
folder: folder,
message: 'Task created. Call task.start() to begin export to Google Drive.'
};
}
module.exports = {
generateExportUrls,
estimatePixelCount,
createDriveExportTask
};