Frequently Asked Questions

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General questions

I have a problem, please help!

Please post a question following this guide, providing as much information as possible (see the Stack Overflow guide to asking good questions). This usually means:

  • sending a link to a script in the Code Editor (click on the "Get Link" button to obtain it)

  • sharing any assets needed to run the script

  • for failed batch tasks, reporting the ID of the failed task. Task ids look like this: 4C25GIJBMB52PXTEJTF4JLGL. They can be found in the Task tab of the Code Editor.

Where can I read about the Earth Engine architecture?

Please see this paper: Gorelick et al. 2017.

See the EDU and Training Resources pages.

See this free EE course by Ujaval Gandhi, which includes a video with an introduction to remote sensing.

Earth Engine programming

What are some common coding errors?

See the debugging guide.

Why can't I use simple math like ee.Image("image") * 2?

In EE you should not mix server-side and client-side objects or operations. All operations on EE objects are performed server-side. Any client-side computations will not do what you intend them to do. Please see this page for more details.

How can I use for loops or if/else statements?

Earth Engine programming is done using a functional language, so loops and conditional operations should be expressed using equivalent concepts like map or filter. Please see this page for more details.

How do I show text labels in my image or video?

There is no built-in support for text labels, but you can:

Can I use some standard color palettes?

Use a third-party JS package ee-palettes.

How do I create my own website that uses Earth Engine?

Use Earth Engine Apps for simple applications. In more complex cases, you can build EE-powered App Engine apps.

How do Map IDs work?

Map IDs (called mapid throughout the API) are keys which allow clients to fetch map tiles. Each ID is a hash created by providing an image expression to the getMapId endpoint. The resulting IDs are keys which point to both the image expression and the user credentials that will be used to generate tiles in a later stage.

Requesting map tiles involves specifying the location of the tile (x, y, zoom) as well as the mapid (the key to the image and credentials). The same ID can be reused to load many map tiles. There are no limits on the reuse of mapid keys, but they expire after a few hours. We don't currently publish guarantees about how long they persist, but any code you write should be resilient to the ID expiring.

Creating these IDs involves storing a small amount of data and validating credentials, so it's best to reuse them for as long as possible. There's no API quota specifically associated with the getMapId endpoint, but any workflow which involves creating mapid objects at a rate anywhere near the rate of fetching tiles is probably doing something wrong. Earth Engine has no API endpoint to remove, list or manage these IDs, since these are transient resources.

Why does ee.Algorithms.If() print both the true and false case?

function a() { print("true"); }
function b() { print("false"); }
// Prints 'true' and 'false'.
ee.Algorithms.If(true, a(), b());

The If() algorithm works just like every other algorithm on Earth Engine in that all its arguments have to be evaluated before the algorithm itself can run. The algorithm gets both the trueCase and falseCase results and then picks and returns one based on the condition argument, but both paths had to be executed in order for those values to be passed into the algorithm in the first place.

I get the error "Request payload size exceeds the limit"

You are trying to send to Earth Engine a very large request. This typically happens when the code uses a lot of client-side 'for' loops or constructs a FeatureCollection out of many geometry objects. In the latter case, instead of creating such geometries in your script, generate a CSV file containing them and upload it into a table asset.

What the difference between ee.Image.clip() and ee.Filter.bounds()?

See this GIS Stack Exchange thread. The ee.Image.clip() function masks out pixels that do not intersect a given ee.Geometry or ee.Feature, making them transparent in visualizations and excluded in computations. You can conceptualize it as clipping off pixels from an image.

The ee.Filter.bounds() function filters ee.Image objects out of an ee.ImageCollection based on image intersection with an ee.Geometry or ee.Feature. It is used to limit the scope of an analysis to only the images that intersect a given region, which helps to optimize expressions.

How to convert image pixels to feature collections, with one feature per pixel?

Use the ee.Image.sample() function. See usage examples on the function's API reference page.

What is the difference between ee.ImageCollection.merge() and ee.ImageCollection.combine()?

The ee.ImageCollection.merge() function merges all of the images from two collections into one collection, regardless of whether their respective images have coincident bands, metadata, CRS, or scale. It is the union of two collections. The combine() method combines the bands of matching images from two collections into a single collection. Matching images share the same ID (system:index property). It is an inner join of two collections based on image ID, where bands from matching images are combined. For matching images, bands from the secondary image are appended to the primary image (overwrite is optional). If there are no matching images, an empty collection is returned.

How to filter image collections on multiple date intervals?

See this GIS Stack Exchange thread. Either merge() multiple collections together or use ee.Filter.or().

How to create a bounding box around a given point?

// Buffer the point by a desired radius and then get the bounding box.
var LNG = -117.298;
var LAT = 45.162;
var point = ee.Geometry.Point([LNG, LAT]);
var buffer = point.buffer(30000); // half of box width as buffer input 
var box = buffer.bounds(); // draw a bounding box around the buffered point
Map.centerObject(box);
Map.addLayer(point);
Map.addLayer(box);

// Map the buffer and bounds procedure over a point feature collection.
var pointCol = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point([LNG + 1, LAT])),
  ee.Feature(ee.Geometry.Point([LNG - 1, LAT]))
]);
var boxCol = pointCol.map(function(feature) {
  var box = feature.buffer(30000).bounds();
  return feature.setGeometry(box.geometry());
});
Map.addLayer(boxCol);

Data Catalog

Can you add dataset X?

File a dataset request bug following this guide.

You can also upload data into your Earth Engine home folder. See Importing Raster Data and Importing Table Data.

An existing dataset has a new version

File a dataset bug following this guide and indicate that you are requesting a dataset update.

An existing dataset is not updated or is missing assets

Before reporting a problem, please verify, if possible, that the desired assets actually exist on the dataset provider's site. See this page for more details.

If you are looking for an asset by filtering an ImageCollection, make sure your filters are not too restrictive.

In particular, note that:

  • Sentinel-2 SR (Level 2 data) were not produced by ESA for early Level 1 scenes.

  • Landsat does not have worldwide coverage before 2000.

An existing dataset has wrong values

Please post on the developers forum. Include a script that zooms into the native resolution of the asset and makes it easy to see what values are wrong. Please explain where exactly you observed the alternative value.

Where else can I ask about datasets?

For questions about NASA datasets, see this forum.

For questions about the toolboxes operating on Copernicus datasets, see the S1, S2, and S3 forums.

How large is the EE catalog?

As of June 2022, the catalog contains about 900 datasets. Its size on disk is over 70 petabytes (after taking into account lossless compression).

How often are data in EE updated?

Normally, all ongoing datasets are updated at least daily (though not all such datasets have new data every day). Some datasets are updated several times a day. However, there is no policy to guarantee the presence of the most recent assets in the catalog.

How do I view the contents of the EE catalog programmatically?

The list of dataset is exported in the STAC format to a Google Cloud Storage bucket gs://earthengine-stac. The entry file is catalog.json.

Can I use Google Maps data or imagery for analysis?

Google does not license or sell basemap data for analysis.

How can I find the date an asset was ingested?

The 'system:version' asset property is the ingestion timestamp, formatted as microseconds since Unix epoch. Here is an example that converts the ingestion timestamp of a Landsat image to a human readable format.

var image = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20210508');
print('Ingest date', ee.Date(image.getNumber('system:version').divide(1000)));

Landsat

How is the simpleComposite algorithm implemented?

The server-side implementation is equivalent to this JavaScript code.

How can I create cloud-free composites from Landsat surface reflectance data?

Landsat Level 2 (surface reflectance) data have several quality bands that can be used to mask out clouds and other unwanted image artifacts. An example of using these bands to process Landsat 8 SR images and create a median cloud-free composite is provided in this GIS Stack Exchange post. The same procedure is used to build a cloud-free composite for use in supervised classification examples in the Developer's Guide.

How can I mask clouds and cloud shadows in MSS imagery?

The third-party msslib module for the JavaScript Code Editor includes an implementation of the MSScvm algorithm, as well as other helpful functions for exploring and preparing MSS data.

Data Management

Who owns the data that I upload?

According to the Earth Engine Terms of Service, customers own the data that they upload to Earth Engine.

I can't upload data!

Please check the upload task status in the Tasks pane in the upper right-hand corner of the Code Editor. You can also view the dedicated task page.

If there is no task, you have probably tried uploading your file through the Code Editor, but due to a networking problem the file never finished uploading, so the task was never created. Please try using a different browser or a different computer.

If there is a failed task, please examine the error it shows. If there is no specific error message, first verify that your file is not corrupt by running gdalinfo for raster files or ogr2ogr for vector files. These commands will try to read all the data from the source files and display errors if the files are corrupt.

Example gdalinfo call:

gdalinfo -mm -stats -checksum file.tif

Example ogr2ogr call that will convert in.shp to out.csv:

ogr2ogr -lco GEOMETRY=AS_WKT -f CSV out.csv in.shp

If the file looks valid, please post the failed task id as text (not as a screenshot) on the developers mailing list. Task ids have this format: 4C25GIJBMB52PXTEJTF4JLGL. Please also make your source file publicly readable if possible. If it's a private file, please share it with just earthengine@google.com if you would like the Earth Engine team to examine it. If it's not possible to share the source file, please at least provide the output of gdalinfo -mm -stats -checksum.

If Earth Engine does not support a certain projection, you will need to reproject the data before uploading using, for example, gdalwarp.

How do I upload a file in NetCDF or another unsupported raster format?

Currently only GeoTIFFs can be uploaded to Earth Engine. Other GDAL-compatible formats can be converted to GeoTIFFs using gdal_translate. Example:

gdal_translate -co COMPRESS=DEFLATE file.nc file.tif

Note that some NetCDF or HDF files consist of multiple subdatasets that can be discovered with gdalinfo. The gdal_translate command in this case will look like this (note that file path between the double quotes):

gdal_translate HDF4_EOS:EOS_GRID:"/tmp/MCD12Q1.A2001001.h00v08.005.2011055224312.hdf":MOD12Q1:Land_Cover_Type_1 file.tif

NetCDF files sometimes do not carry a projection that GDAL recognizes. In this case you would need to set the projection and spatial extent in the gdal_translate command line. Example:

gdal_translate -a_srs EPSG:4326 -a_ullr -180 90 180 -90 file.nc file.tid

My raster ingestion has been running for days and has not finished.

Using gdalinfo, check if your file has the following GDAL option set: INTERLEAVE=PIXEL. For files with this option and many bands, ingestion might never finish because the layout of such files makes reads very slow.

Try converting such files to the band-interleaved layout before uploading:

gdal_translate -co "INTERLEAVE=BAND" src.tif dst.tif

My uploaded rasters do not match the basemap.

If the data are slightly offset from the basemap, the projection probably has an incorrect datum (assumption about the shape of the Earth). This happens most often with the sinusoidal projection that cannot be fully encoded in GDAL metadata. When you know what the target projection should be (e.g., SR-ORG:6974 for files using MODIS sinusoidal projection), set the --crs flag during command-line upload or the crs field of the upload manifest.

If the data appear grossly distorted and/or in the completely wrong place, the projection or the affine transform is likely wrong.

My raster only shows up over the Eastern hemisphere.

You probably uploaded a global raster that spans the longitude range [0, 360]. However, Earth Engine requires rasters to be in the range [-180, 180]. Please swap the left and right halves of the raster before ingestion. See these GIS Stack Exchange suggestions.

Why does my ingested classification image look speckled?

You probably used the default MEAN pyramiding policy. For classification images, the MODE pyramiding policy should be used. for QA/bitmask images, the SAMPLE pyramiding policy should be used.

I get the following error: No data value -128.0 cannot be applied to band #0 of type Short<0, 255>.

GDAL cannot treat single-byte bands as containing signed integers, so it reads such bands as unsigned integers. This would conflict with negative no data values.

If your values are actually signed integers, use manifest upload and add this to the tileset section containing your file: data_type: "INT8"

If your values are unsigned integers, your file has a bad nodata value. You can override it on upload with the correct data value (or a value that never occurs, if one exists). You can also use gdal_translate -a_nodata to change the nodata value or gdal_edit.py -unsetnodata to remove it.

How do I upload a file in the GeoJSON or another unsupported vector format?

Use ogr2ogr to translate OGR-compatible formats into CSV or SHP. Example:

or2ogr -f "ESRI Shapefile" file.shp file.kml

Note that in CSV uploads, the geometry column can contain GeoJSON.

I want to upload data using Python, or upload many files at once.

Use command-line upload. Such uploads require source files to be first placed into a GCS (Google Cloud Storage) bucket. GCS usage does not cost anything if you stay within the free tier limits - see the pricing page.

I want to upload a large raster mosaic split into many tiles.

If the files all have the same projection and pixel size, just upload them together into the same asset — they will be mosaiced automatically.

If the files have different projections or pixel sizes, they cannot be mosaiced into a single raster asset. Instead, upload each tile as a separate asset into the same ImageCollection that can be mosaiced using ImageCollection.mosaic()

I am trying to upload a mosaic and get errors about mismatched tiles.

Tiles for Earth Engine raster mosaics must have the same projection and pixel size. In addition, the tiles must align exactly on pixel boundaries.

I am trying to upload a file from a GCS bucket, but Earth Engine cannot find it.

You may have used different Google accounts for the GCS upload and for connecting to Earth Engine. Make sure the GCS file is readable by the account you use to connect to Earth Engine. If browser multilogin makes this confusing, connect to Earth Engine in an anonymous/incognito browser window.

I want to export many assets at once.

We are working on a single-command export of ImageCollections. For now, please export each image separately.

I want to move or delete a Folder or an ImageCollection with a single command.

Currently you have to first move or delete each asset, then move or delete the parent folder or collection. If there are a lot of child assets, write a shell or Python loop to iterate over them.

I want to directly access Earth Engine data from outside of EE.

QGIS has an Earth Engine plugin.

GDAL has an Earth Engine driver.

Other systems can use the EE REST API.

I would like to update a part of my Earth Engine asset without completely reingesting it.

Currently it's not possible to update raster or vector data uploaded into EE. Only asset metadata properties can be updated.

I am losing access to my account. What do I do with my assets?

If the policies of the original account allow data transfer, please share your assets with another account, then copy the assets to be owned by the new account. Use the command-line copy utility if there are many assets to move.

If an account is deleted, the assets owned by it are no longer accessible.

My exported image is in the wrong place.

For some projections, such as sinusoidal or conic, GeoTIFF files sometimes cannot store all the necessary projection parameters. This results in an exported file that appears in the wrong place when viewed in desktop GIS tools or reingested into EE.

To fix this, specify an export crs parameter that's known to work well with GeoTIFF files—for example, use the EPSG code for the UTM zone containing your area of interest.

Code Editor

I cannot log in to the Code Editor because it prompts me to use the wrong account.

Please log out, select the account that is registered to use Earth Engine in the "Choose an account" page, and then re-select the same account in the second "Choose an account to continue to Earth Engine Code Editor" page (exact wording may be different).

I want to screenshot a global map, but don't like the Web Mercator projection.

The map projection used in the Code Editor is Web Mercator ('EPSG:3857'). It inflates the size of objects away from the equator, making high latitude regions appear much larger than they actually are, as compared to regions near the equator. You cannot change the projection of the Code Editor's map canvas, but you can "paint" an image in the projection of your choice to the Web Mercator canvas using the ee.Image.changeProj method. See the method's API reference page for an example of displaying a global DEM to the Code Editor map in the Robinson projection. Note that this technique should only be used for visualization purposes, as the Code Editor's inspector and drawing tools are still operating in Web Mercator.

My script does not save (Script error: Unknown commit).

If you receive a Script error: Unknown commit message when saving a script, it likely means that the repository that you are saving to is out of sync. The cause of this state is variable and difficult to identify. To resolve the issue, try refreshing the script list using the button in the upper right corner of the Script tab. If that does not work, try creating a new repository from the New button in the Script tab and saving your script there (you may need to move scripts into the new repo from the out-of-sync repo).