I am building a ui in Earth Engine by following this example.. https://google.earthengine.app/view/forest-change

The example code can be found here.. https://code.earthengine.google.com/b02a58539a6374cdebd9416729a08f47

The snippet of code that influences the output of the opacity slider can be seen below...

opacitySlider.onSlide(function(value) {
  mapPanel.layers().forEach(function(element, index) {

This function subsequently influences the opacity of every layer in the map panel.

I have additional functionality in my application that adds other boundaries/imagery that I would like to keep rendered on the map, even if the opacity slider is active.

Is there an easy way to specify only a select group of layers in the map panel to work with the opacity slider?

I am aware that there is a default layer panel with individual opacity sliders, but I'd like to keep that control hidden from the app.

1 Answer 1


When you add layers (that is, ui.Map.Layer objects, not images), remember them in a variable:

var opacityChangingLayers = [];
for (var key in layerProperties) {
  ... // Set up `masked` here...

  // Put the layer in a variable, ...
  var mapLayer = ui.Map.Layer(masked, {}, key, layer.defaultVisibility);
  // ... add it to the map, ...
  // ... and *also* put it in the array of layers we want to change.

Then change only those layers:

  opacityChangingLayers.forEach(function(element) {
  • I have tried implementing your suggestions without success. I think I am just coding your solution into my app incorrectly. Here is a link to a working version of my application.. code.earthengine.google.com/a5d78cbba1ebe4494e9fc674900d95ec. I am trying to code the opacity slider to only work for the layers in the drop-down list Jan 26, 2021 at 18:29
  • @EliSimonson You should not put image objects in opacityChangingLayers; the line I wrote var opacityChangingLayers = []; is complete as-is. Only map layers go in that array, and that is done by the line opacityChangingLayers.push(mapLayer);
    – Kevin Reid
    Jan 26, 2021 at 20:32
  • @EliSimonson You also need to correctly incorporate the code I wrote in the first section: the layer object that needs to be pushed is, again, not the image: it is the object that ui.Map.Layer returns.
    – Kevin Reid
    Jan 26, 2021 at 20:33
  • Yup, your solution worked just fine when I saved the images as layer objects!! Jan 29, 2021 at 19:16

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