remove restore should handle land data separately

[alessandrofelder]

currently remove-restore doesn't distinguish bathymetry and topography data, but the GEBCO suggests to do this.

[JamieJQuinn]

@alessandrofelder Have you got a reference for where GEBCO recommends doing this?

[alessandrofelder]

Fig 8.4 on page 148 of the GEBCO Cookbook. There seem to be steps D1 and D2 for water and land data?

[alessandrofelder]

I guess we could call remove-restore separately on data sets we filtered using GDAL beforehand to that effect... 🤔