I want to extract NDVI values on each pixel (like ASCII files in GIS) for every time step over the last 20 years period for given catchments using Google earth engine. I don't know as how to proceed if I want all the tiff files over every time step.
NDVI data can be downloaded as NetCDF format or GeoTiff. Both can be converted to superoverlays with gdal utilities to KMZ or KML for use in Google Earth and will retain pixel resolution you are looking for. The raster pixel data comes usually as floating point numbers. To convert from floating point you can again use gdal "first" to a gray scale or color scale using "gdal_dem" by using a color.txt file to map from float to color. Then convert your "color" GeoTiff to a superoverlay KML or KMZ. To make a time series out of the (KMZ or KML) files try this link:
https://www.linkedin.com/pulse/building-time-lapse-imagery-google-earth-engine-andrew-cutts/
For each (KMZ or KML) file would be one time frame in the times series and you would have to set time tags in each file for this to work. The biggest problem i think you will have is the size of the original files (NetCDF or GeoTiff) and 20 years is a lot of data to be processed. Hope this suggestion helps.
For your shapefile cut out of the geotiff you can use this:
https://gis.stackexchange.com/questions/45053/gdalwarp-cutline-along-with-shapefile
gdalwarp -cutline INPUT.shp -crop_to_cutline -dstalpha INPUT.tif OUTPUT.tif
to create simple NDVI time-series from single points or polygons, you can also use the EO Browser: https://apps.sentinel-hub.com/eo-browser/
A tutorial is given here:
https://www.youtube.com/watch?v=m3pron0C0kE
Creating a graph starts at 1:55
Hello Uday Pimple ,
Thanks for your response and sorry for being slow in response. I tried to complete my task however, now I am struggling in exporting my images. Here is the portion of my code, where I need to export all the images in my "meanCollection" variable (it has 12 images i.e for each month). I am struggling in exporting all the 12 images into my google drive (Way - I). I also tried to the other way round to just export the movie scene for all this 12 images but I was not able to export them as it is catchment not a polygon (Way -II).
// Image collections for NDVI for the last some number of years, one value per month.
var collection =ee.ImageCollection(allsats.filterDate('2000-01-01','2017-01-01'));
collection = collection.filterBounds(thisShape);
//Trim out regions outside out analysis
collection = collection.map(function(img){
return img.clip(thisShape);
});
//Loop through each month and make average
var imgList = ee.List([]);
for (var month = 1; month
Hello Reuben Reyes ,
Thanks for your response.
I was not know about a way to work with the gdal method for working on NDVI matters, hence thanks a lot for making my vision toward this side. However, I want work on the spatial NDVI plots as I was able to work upon the time series NDVI PLOT.
Secondly, regarding the building of time-lapse imaginary on GEE was really helpful site for me. I have doubt, as we can extract those images or not.
Thank you
Hello Andreas Braun
Thanks for your suggestion.
I am still searching for spatial NDVI analysis portion, as I was able to do the time series plot.
Thank you,
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