Warn more clearly about space demand of WorldClim data, reduce .asc file size

[platipodium]

openjournals/joss-reviews#8845

The sheer size of even the low-resolution data (1 GB for Europe at 10minutes) is overwhelming. There should be more transparent information on the disk space demand for using logoclim with any of that data.

[platipodium]

With some effort, you can easily cut down local file storage by more than 50%. Have a look at one of the CRU TS files as .asc:

-9999 -9999 -9999 -9999 -9999 7 -9999 -9999 -9999 -9999 -9999 -3.3333332538604736328 -3.75 -4.25 -9.5833330154418945312 -9.5 -9.25 -9.375 -9.6000003814697265625 -9.6666669845581054688 -9.6999998092651367188 -8.1666669845581054688 -7.25 -2.6153845787048339844 -2.0666666030883789062 6.1428570747375488281 7 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 6 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 6 1.5 3.1666667461395263672 6 6 6 6 6 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999

• For temperature, a missing-value marker of 99 instead of -9999 saves 60% storage space, for other variables potentially even more
• Precision is unnecessarily high, by limiting to 3 significant digits, you can save even more space.

This should be straightforward to implement as the generation scripts are in R anyway.

[danielvartan]

With some effort, you can easily cut down local file storage by more than 50%.

Good idea! I used -9999 because it’s the default value for the NODATA field in the Esri ASCII Grid.

For this application, two significant digits (-99) are sufficient, since the only variables with negative values are temperature, and the lowest natural temperature ever directly recorded seems to be -98 °C.

I’m implementing the Quarto notebooks as functions in the orbis R package to facilitate use. I've already changed the default NODATA value of wc_to_ascii to -99 and added a note about this in the documentation.