Re:Table of offsets – Import/Export

[Marven]

John,

Basically there are two ways to recreate an existing design:

1. By importing offsets from an offsets table, or a similar file format. In this case the software will create a surface that approximates the given points as closely as possible. To obtain the best fit of the surface the generated control points may be scattered, which is not very intuitive to work with. In almost any case it still requires additional manual fairing and stitching, depending on the shape of your ship and the number of points in your offsets table.
2. An alternative way which requires slightly more work but gives better results in almost any case is to use markers or an image as a background reference. You can start a new design and model it to fit your reference lines, as described in my previous post. Personally I prefer this over importing offsets since the distribution of controlpoints is in your own hand which makes it easier to fair the surface.

To better understand the problem of exporting/importing offsets you need to consider the fact that offsets or generated only at the intersection of waterlines and stations. A lot of crucial information, such as the shape of your keelline, the startpoint and endpoint of waterlines cannot be specified according this format, so by importing an offsets table a lot of information is lost.

Now in the old days this wasn’t really a problem since the loftsman would fill in the gaps. A computer system in most cases misses the intelligence to do this in an estethically pleasing way, and it also has the disadvantage that the surface must comply with the mathemathics behind it.

The second method above overcomes these problems, but it requires slightly more work.