CODEWITHSUNDEEP
mergeqgisgoogle-earth-engine
lcasse
lcasse

Reputation: 3

How to create a feature collection with mean values of certain features and the location/shape of a different feature collection?

I have two feature collections one containing point data with measurements and the other polygons marking the different clusters where several measurements were taken close together. In Google earth engine I am trying to create a new (point) feature collection (or edit the polygon features) which contain the average measured values for every seperate cluster.

I used the following code to join the two different feature collections (so that the polygons also contain the point data):

 var mean = ee.Filter.intersects({
    leftField: '.geo',
    rightField: '.geo'
  })

var saveAllJoin = ee.Join.saveAll({
  matchesKey: 'Measurements',
})

var intersect = saveAllJoin.apply(Clusters, Measurements, mean)

However, since multiple measurements are taken within one cluster this results in a featurecollection that contains a list with the measurement points located within a specific cluster. Instead I am looking for the average measured values as a property of the polygons. What is the way to do this in Google earth engine (or possibly in QGIS)?

I have tried using ee.FeatureCollection.map in order to calculate the mean value at every individual polygon:

var clust = ee.FeatureCollection(Clusters).map(function(feature) {
  var meanClay = Measurements.reduceColumns({
    reducer: ee.Reducer.mean(),
    selectors: ['Clay']
  })
  return feature.set('mean', meanClay)
})

Now if I print the variable "clust" I get a featurecollection with mean values for the (measured) attribute clay. However, every feature gets the same value (the mean of all the measured points instead of just those within a specific cluster).

For clarity: I got a shapefile with 78 measurement locations (points) which are loaded into my script as a featurecollection and contain the measured values. Besides this I also have a shapefile with polygons indicating 16 areas where a cluster of measurements were performed (so around 4-5 measurements in each cluster). Now I am trying to get the average of all the measurements (points) within each polygon (cluster) for every individual polygon.

Upvotes: 0

Views: 1368

Answers (1)

lcasse
lcasse

Reputation: 3

I solved it by using filterBounds() on the point data. Here the filterBounds is used to filter the point data to only consist of the points within a specific cluster.

var clust = ee.FeatureCollection(Clusters).map(function(feature) {
  var meanClay = ee.FeatureCollection(Measurements.filterBounds(feature.geometry()))
    .reduceColumns({
      reducer: ee.Reducer.mean(),
      selectors: ['Clay']
    })
  return feature.set(meanClay)
})

Upvotes: 0

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