Google Earth Engine Error – Fixing Dictionary.set Parameter ‘value’ is Required

classificationgoogle-earth-engineland-cover

I'm attempting to calculate the proportion of landcover classes for each county in Oregon in GEE and export values as a CSV, but I get the following error: Error: Error in map(ID=00000000000000000000): Dictionary.set: Parameter 'value' is required. (Error code: 3). I see this question was asked before, but not answered. Can someone help me address this error?
Here is my Code.

snippet of the code:

//calculate area of each class for each county in the shapefile
var calculateClassArea = function(feature) {
  var areaImage = ee.Image.pixelArea().addBands(ORlandcover);
  
  var areas = areaImage.reduceRegion({
    reducer: ee.Reducer.sum().group({
      groupField: 1,
      groupName: 'class',
    }),
      geometry: feature.geometry(),
      scale: 30,
      maxPixels: 10364007075
  });
  var classAreas = ee.List(areas.get('groups'));
  var classAreasLists = classAreas.map(function(item) {
    var areaDict = ee.Dictionary(item);
    var classNumber = ee.Number(
      areaDict.get('class')).format();
      var area2 = ee.Number(
        areaDict.get('sum')).divide(1e6).round();
        return ee.List([classNumber, area2]);
  });
  var result = ee.Dictionary(classAreasLists.flatten());
  var county = feature.get('Name');
  return ee.Feature(
    feature.geometry(),
    result.set('county', county));
};

var countyAreas = table.map(calculateClassArea);
//print(countyAreas);

var classes = ee.List.sequence(1, 16);
var outputFields = ee.List(
    ['county']).cat(classes).getInfo();
 
Export.table.toDrive({
    collection: countyAreas,
    description: 'class_area_by_county',
    folder: 'GEO Stuff',
    fileNamePrefix: 'class_area_by_county',
    fileFormat: 'CSV',
    selectors: outputFields
    })

Best Answer

Issue can be solved as follows ('set' method is not adequately used with ee.Feature object and it is also eliminated selectors parameter in Export.table):

//calculate area of each class for each county in the shapefile
var calculateClassArea = function(feature) {
  var areaImage = ee.Image.pixelArea().addBands(ORlandcover);
  
  var areas = areaImage.reduceRegion({
    reducer: ee.Reducer.sum().group({
      groupField: 1,
      groupName: 'class',
    }),
      geometry: feature.geometry(),
      scale: 30,
      maxPixels: 10364007075
  });
  var classAreas = ee.List(areas.get('groups'));
  var classAreasLists = classAreas.map(function(item) {
    var areaDict = ee.Dictionary(item);
    var classNumber = ee.Number(
      areaDict.get('class')).format();
      var area2 = ee.Number(
        areaDict.get('sum')).divide(1e6).round();
        return ee.List([classNumber, area2]);
  });
  var result = ee.Dictionary(classAreasLists.flatten());
  var county = feature.get('Name');
  return ee.Feature(feature.set('result', result));
};

var countyAreas = table.map(calculateClassArea);
print("countyAreas", countyAreas);

var classes = ee.List.sequence(1, 16);
var outputFields = ee.List(
    ['county']).cat(classes).getInfo();

print(outputFields);

Export.table.toDrive({
    collection: countyAreas,
    description: 'class_area_by_county',
    folder: 'GEO Stuff',
    fileNamePrefix: 'class_area_by_county',
    fileFormat: 'CSV',
    });

After running the task in GEE code editor (link here), without any error, I got following CSV file opened with LibreOffice.

Related Solutions

[GIS] Earth engine error: Layer 1: Layer error: Image.visualize: Parameter ‘image’ is required

There is no image in this time interval. You can test this by simply add a print image line.

var image = ee.ImageCollection('LANDSAT/LT04/C01/T1_TOA')
.filterDate('1984-04-01', '1990-12-31')
.sort('CLOUD_COVER')
.first();

print(image)

var visParams = {
bands: ['B3', 'B2', 'B1'],
min: 0,
max: 3000,
gamma: 1.4, };
Map.addLayer(image, visParams);

If you change the dates to e.g. 1990 than you can see a image inside the collection.

Google Earth Engine Error – Required Parameter ‘Value’ for Image.Constant

Here's how to understand the error message:

In Earth Engine, an argument being null is usually the same as it being omitted. Hence, a call to Image.constant with the value null will produce the error Image.constant: Parameter 'value' is required. This probably explains why you are getting this error despite not having written a misformed call to Image.constant.
But you don't have any Image.constant in your script, it seems. What you do have is img.expression("(NDVI-min)/(max-min)", ...) and you are passing in numbers. This implicitly creates a call to Image.constant to convert those numbers to constant images.
Therefore, we can conclude that either min or max were null. This could happen if for whatever reason there were no pixels intersecting the region of interest, so the minimum/maximum is undefined.

I confirmed this theory by using your reduceRegion parameters with ee.Reducer.count(): img.reduceRegion({reducer: ee.Reducer.count(),geometry:roi, bestEffort:true, scale: 30}) and replacing the image computation with returning a feature holding these counts in the properties. This showed that some of the selected images (may not be the same as yours, since I didn't use the same roi which you did not include in your question) had NDVI bands that had zero pixels counted.

In order to avoid this error, you can map to add the results of the reductions as properties to the features, filter out features with null values with ee.Filter.notNull, then map to compute the result you want (see Justin Braaten's answer for code).

Best Answer

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[GIS] Earth engine error: Layer 1: Layer error: Image.visualize: Parameter ‘image’ is required

Google Earth Engine Error – Required Parameter ‘Value’ for Image.Constant

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