Clever Geek Handbook

Google Earth Engine (GEE) como superordenador público

Servicio de motor de Google Earthbrinda la oportunidad de trabajar con grandes cantidades de información espacial de forma gratuita. Por ejemplo, en cuestión de minutos puede obtener un mosaico compuesto (imagen compuesta) de un millón de imágenes espaciales. Suponiendo que cada escena (conjunto de canales espectrales) de Landsat 8 ocupa 1 GB en forma comprimida, esta solicitud procesa un volumen de información de aproximadamente 1 PB. Y todo esto está disponible de forma gratuita, rápida y en cualquier momento. Pero existe la opinión (incorrecta) de que GEE en cuentas gratuitas le permite procesar y exportar solo pequeños conjuntos de datos. De hecho, esta impresión se debe solo al hecho de que puede comenzar a programar en GEE sin siquiera leer la documentación del servicio, pero no podrá extraer muchos datos sin leer la documentación.A continuación, consideraremos tres soluciones diferentes al problema de vectorizar rásteres y de dos formas diferentes escribiremos una función GEE del lado del servidor para calcular el geohash.















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var points_with_attributes = Image.reduceRegion({
  reducer: ee.Reducer.toList(Image.bandNames().size()),
  geometry: points
})


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var attributes = Image.reduceRegion({
  reducer: ee.Reducer.toList(Image.bandNames().size()),
  geometry: some_area
})


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var latlon = ee.Image.pixelLonLat()
var points_with_attributes = image
  .addBands(latlon)
  .reduceRegion({
    reducer: ee.Reducer.toList(),
    geometry: some_area
  });


ee.Image.pixelLonLat() , . , ( , GEE , , ). , , :







var latlon = ee.Image.pixelLonLat().reproject(image.projection())
var points_with_attributes = image
  .addBands(latlon)
  .reduceRegion({
    reducer: ee.Reducer.toList(),
    geometry: some_area
  });


, :







var latlon = ee.Image.pixelLonLat()
var points_with_attributes = image
  .addBands(latlon)
  .add(image.select(0).add(0))
  .reduceRegion({
    reducer: ee.Reducer.toList(),
    geometry: some_area
  });


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var latlon = ee.Image.pixelLonLat()
var points_with_attributes = image
  .sample({
    region: some_area,
    geometries: true
  });


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var geohash_accumulate = function(obj, list) {
  // define common variables
  var base32 = ee.String('0123456789bcdefghjkmnpqrstuvwxyz'); // (geohash-specific) Base32 map
  // get previous state variables
  var prev = ee.Dictionary(ee.List(list).get(-1));
  var lat = ee.Number(prev.get('lat',0));
  var lon = ee.Number(prev.get('lon',0));
  var idx = ee.Number(prev.get('idx',0));
  var bit = ee.Number(prev.get('bit',0));
  var evenBit = ee.Number(prev.get('evenBit',1));
  var geohash = ee.String(prev.get('geohash',''));
  var latMin = ee.Number(prev.get('latMin',-90));
  var latMax = ee.Number(prev.get('latMax',90));
  var lonMin = ee.Number(prev.get('lonMin',-180));
  var lonMax = ee.Number(prev.get('lonMax',180));

  // calculate substep bit step idx
  // bisect E-W longitude
  var lonMid = ee.Number(ee.Algorithms.If(evenBit.gt(0),                      lonMin.add(lonMax).divide(2), 0)      );
  idx =        ee.Number(ee.Algorithms.If(evenBit.gt(0).and(lon.gte(lonMid)), idx.multiply(2).add(1),       idx)    );
  lonMin =     ee.Number(ee.Algorithms.If(evenBit.gt(0).and(lon.gte(lonMid)), lonMid,                       lonMin) );
  idx =        ee.Number(ee.Algorithms.If(evenBit.gt(0).and(lon.lt(lonMid)),  idx.multiply(2),              idx)    );
  lonMax =     ee.Number(ee.Algorithms.If(evenBit.gt(0).and(lon.lt(lonMid)),  lonMid,                       lonMax) );
  // bisect N-S latitude
  var latMid=  ee.Number(ee.Algorithms.If(evenBit.eq(0),                      latMin.add(latMax).divide(2), 0)      );
  idx =        ee.Number(ee.Algorithms.If(evenBit.eq(0).and(lat.gte(latMid)), idx.multiply(2).add(1),       idx)    );
  latMin =     ee.Number(ee.Algorithms.If(evenBit.eq(0).and(lat.gte(latMid)), latMid,                       latMin) );
  idx =        ee.Number(ee.Algorithms.If(evenBit.eq(0).and(lat.lt(latMid)),  idx.multiply(2),              idx)    );
  latMax =     ee.Number(ee.Algorithms.If(evenBit.eq(0).and(lat.lt(latMid)),  latMid,                       latMax) );
  // check position
  evenBit = evenBit.not();
  bit =     bit.add(1);
  geohash = ee.String(ee.Algorithms.If(bit.eq(5), geohash.cat(base32.slice(idx,ee.Number(idx).add(1))), geohash));
  idx =     ee.Number(ee.Algorithms.If(bit.eq(5), ee.Number(0), idx));
  bit =     ee.Number(ee.Algorithms.If(bit.eq(5), ee.Number(0), bit));

  // return state
  var curr = prev
    .set('idx',     idx     )
    .set('bit',     bit    )
    .set('evenBit', evenBit)
    .set('geohash', geohash)
    .set('latMin',  latMin )
    .set('latMax',  latMax )
    .set('lonMin',  lonMin )
    .set('lonMax',  lonMax );
  return ee.List([curr]);
};
function geohash_encode(lat, lon, precision) {
  var init = ee.Dictionary({lat: lat, lon: lon})
  var state = ee.List.sequence(1,precision*5).iterate(geohash_accumulate, ee.List([init]))
  return ee.String(ee.Dictionary(ee.List(state).get(-1)).get('geohash'))
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    








// PostGIS check from https://postgis.net/docs/ST_GeoHash.html
print (ee.Algorithms.If(geohash_encode(48, -126, 20).compareTo('c0w3hf1s70w3hf1s70w3'),'Error','OK'));
// Google BigQuery check from https://cloud.google.com/bigquery/docs/reference/standard-sql/geography_functions#st_geohash
print (ee.Algorithms.If(geohash_encode(47.62, -122.35, 10).compareTo('c22yzugqw7'),'Error','OK'));


geohash_encode() geohash_accumulate() 5 . , GEE , . ? "calculate substep bit step idx" geohash_accumulate() ( , ). . , -, , , :







var geohash_accumulate = function(obj, list) {
  // define common variables
  var range4 = ee.List.sequence(0,4).map(function(val){return ee.Number(val).multiply(1/4)});
  var range8 = ee.List.sequence(0,8).map(function(val){return ee.Number(val).multiply(1/8)});

  // get previous state
  var prev = ee.Dictionary(ee.List(list).get(-1))
  var lat = ee.Number(prev.get('lat',0))
  var lon = ee.Number(prev.get('lon',0))
  var n = ee.Number(prev.get('n',0)).add(1)
  var geohash = ee.String(prev.get('geohash',''))
  var latMin = ee.Number(prev.get('latMin',-90))
  var latMax = ee.Number(prev.get('latMax',90))
  var lonMin = ee.Number(prev.get('lonMin',-180))
  var lonMax = ee.Number(prev.get('lonMax',180))

  // calculate step n
  var base32 = ee.String(ee.Algorithms.If(n.mod(2).eq(1), '028b139c46df57eghksujmtvnqwyprxz', '0145hjnp2367kmqr89destwxbcfguvyz'));
  var latRange = ee.List(ee.Number(ee.Algorithms.If(n.mod(2).eq(1), range4, range8)));
  latRange = latRange.map(function(item){return ee.Number(item).multiply(latMax.subtract(latMin)).add(latMin)});
  var lonRange = ee.List(ee.Number(ee.Algorithms.If(n.mod(2).eq(1), range8, range4)));
  lonRange = lonRange.map(function(item){return ee.Number(item).multiply(lonMax.subtract(lonMin)).add(lonMin)});
  var latIdx = latRange.indexOf(latRange.filter(ee.Filter.lte('item', lat)).get(-1));
  latIdx = ee.Number(ee.Algorithms.If(latIdx.gte(latRange.size().add(-1)), latIdx.add(-1), latIdx));
  var lonIdx = lonRange.indexOf(lonRange.filter(ee.Filter.lte('item', lon)).get(-1));
  lonIdx = ee.Number(ee.Algorithms.If(lonIdx.gte(lonRange.size().add(-1)), lonIdx.add(-1), lonIdx));
  var idx = lonIdx.multiply(latRange.size().add(-1)).add(latIdx);
  // reset bounds
  latMin = latRange.get(latIdx)
  latMax = latRange.get(latIdx.add(1))
  lonMin = lonRange.get(lonIdx)
  lonMax= lonRange.get(lonIdx.add(1))
  // define geohash symbol
  var geohash = geohash.cat(base32.slice(idx,ee.Number(idx).add(1)));

  // return state
  var curr = prev
    .set('n',       n       )
    .set('geohash', geohash )
    .set('latMin',  latMin  )
    .set('latMax',  latMax  )
    .set('lonMin',  lonMin  )
    .set('lonMax',  lonMax  );
  return ee.List([curr]);
};
function geohash_encode(lat, lon, precision) {
  var init = ee.Dictionary({lat: lat, lon: lon})
  var state = ee.List.sequence(1,precision).iterate(geohash_accumulate, ee.List([init]))
  return ee.String(ee.Dictionary(ee.List(state).get(-1)).get('geohash'))
}


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