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There are many situations where a user is only interested in a subset of the dataset spatial domain.
For example, when comparing modelled river flow against observations, it is reasonable to being able to extract the timeseries at those point coordinates rather than dealing with many GB of data.
Similarly, when the focus is on a specific catchment it is likely that you want only that part of the spatial domain.
In summary, there two operations that are very popular on CEMS-Flood datasets:
- Area cropping
- Time series extraction
There are two scenarios to perform those operations:
- Remotely - Using the CDS API to perform the operation remotely on the CDS compute nodes and retrieve only the reduced data.
- Locally - Using the CDS API to retrieve the entire data and perform the operation locally.
Settings for
For the exercise on extracting time series on the local machine, we are going to use the latitude and longitude coordinates from a tiny subset of the GRDC dataset.
Copy the content of the box below into an empty file named "GRDC.csv", the file should reside in your working folder.
Retrieve the following datasets:
GloFAS
CDS API
Time series extraction:
Area cropping:
Local machine
Time series extraction:
Area cropping:
EFAS
Coordinates precision
When transforming from lat/lon (source coordinates) to projected LAEA (target coordinates), you need to consider that the number of decimal places of the source coordinates affects the target coordinates precision:
An interval of 0.001 degrees corresponds to about 100 metres in LAEA.
An interval of 0.00001 degrees corresponds to about 1 metre in LAEA.
CDS API
to update once cropping works....
Time series extraction:
Area cropping:
Local machine
Time series extraction:
We are going to extract EFAS reforecast's timeseries at locations defined by latitude and longitude coordinates from a tiny subset of the GRDC dataset.
Important - Download upstream area
EFAS's x and y coordinates, when converted from GRIB to NetCDF, are not projected coordinates but matrix indexes (i, j), It is necessary to download the upstream area static file that contains the projected coordinates and replace it in EFAS.