I have been reading the documentation and some related questions online, but I cannot seem to make it work. I use Google Earth Engine to access an old Landsat 5 image, and classify later on.

I want to plot the spectral signatures on a chart in earth engine, but I cannot seem to make it work.

This is the error code I keep getting:

Error generating chart: Data column(s) for axis #0 cannot be of type string

As far as I know, all the properties in the FeatureCollection are numeric. I don't know where the strings might come from.

Can anyone explain what is exactly going wrong?

The code:

// Query satellite image  26.996813, 14.395989
var aoi = ee.Geometry.Rectangle([14.38, 26.98, 14.49, 27.87]);
var collection = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR').filterDate('1995-01-01', '1995-01-30').filterBounds(aoi).filterMetadata('IMAGE_QUALITY', 'equals', 9).select(['B1', 'B2', 'B3', 'B4', 'B5', 'B6', 'B7']);

//var rgbImage = collection.sort('CLOUD_COVER').first().select(['B3', 'B2', 'B1']);
var image_ = collection.sort('CLOUD_COVER').first();

// Load training data
var trainData = ee.FeatureCollection('users/jneujens/trainData');

// Property containing land cover labels
var label = 'classname';

// Get training from polygons on image
var training = image_.sampleRegions({
  collection: trainData,
  properties: ['classvalue'],
  scale: 30


// Graph of spectral signatures training data
var options = {
  title: 'Landsat 5 surface reflectance spectral signatures',
  hAxis: {title: 'Wavelength (micrometers)'},
  vAxis: {title: 'Reflectance'},
  lineWidth: 1,
  pointSize: 4,
  series: {
    0: {color: 'grey'}, // impervious
    1: {color: 'green'}, // vegetation
    2: {color: 'red'}, // soil

// Define a list of Landsat 8 wavelengths for X-axis labels.
var wavelengths = [0.47, 0.56, 0.66, 0.83, 1.56, 2.2, 11.4];

// Create the chart and set options.
var spectraChart = new ui.Chart.image.regions(
    image_, training, ee.Reducer.mean(), 30, 'classvalue', wavelengths)

  • Hi Joost! When posting a question please remember to share private assets so that we can all run your code. If your data are not available for sharing, please try to provide a toy script that reproduces the problem. Jan 9, 2020 at 21:48

2 Answers 2


Try providing trainData as the regions argument to ui.Chart.image.regions() instead of training. The .sampleRegions() step is unnecessary and it may be altering your original collection.


try using remap function to convert the class values from string to integers

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.