page under construction ------------------------------
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 different ways to perform those operations:
- From the CDS API (less data is downloaded)
- Locally (full control on the process)
GloFAS
Example script to crop and extract time series from different GloFAS products:
CDS API
Local machine
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....
Local machine
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 data's x and y coordinates 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.
Copy the content into an empty file named "GRDC.csv", the file should reside in the same folder of the efas_reforecast.grib file and the upstream area.
Cropping to a bounding box.