In calc_bathy the age of reconstruction isn't always necessary

[Diego635]

Problem:

The tool now asks the user to enter the time of reconstruction and assumes the ages of the raster are relative to present-day. This tool also requires the raster to be rotated so that the gaps for the continents are at the right position (at the time of reconstruction). This is only possible is the user reconstructs the whole with static polygons in GPlates like Baatsen did. However if the user takes the age grid raster from other sources (e.g.: Müller) the ages might be already expressed relative to the time of reconstruction and not to the present-day. In this case the time to be specified in "time of reconstruction" is 0 Ma. This makes everything very confusing and the way it's explained now is misleading.

Possible solution:

We could implement two fields:

• In one field we would ask for the time the ages of the rester are relative to.
• In the other field we would ask for the time of reconstruction.

Then we make the difference. If both times are the same, the result will be 0 as we don't need to use the time of reconstruction to calculate the bathymetry. If the times are different, we use the difference.

[jaminzoda]

Fixed in b05710e37eb72ac576341e404626623daa87f054.