I get a CSV file from a survey in Spcapaflow Bay (many great wrecks famous for diving)with 4250000 points but depth is négative, can we have the choose when importing such file to choose positve or negative depth? (surface 5km x 5km)

A very easy way:
Just open your csv with an editor - wordpad works fine - and replace the - (minus) signs by nothing, so that all the - signs will be deleted.

Hubert wrote: It works automatly because 4250000 lines!!

Any reasonably good text editor with "search and replace" will do that. Notepad++ for example - notepad-plus-plus.org/

Nice link Nick - great data!
I downloaded a section for an area I fish a lot - all gridded on 2m, which is a little extreme. The first image below is track data in a single project, with nearly 4M points - probably nearing the practical limit for RM:





and contour and 3D maps:





I must admit I modified a development version of RM to accept -ve depths. I will think about adding an option to the equipment profile for CSV.

Hi Nick,
I put the file you sent through RM. 4.5M points is a lot, but it got through it. I set the cone angle to 1 degree, as with LIDAR data that really doesn't apply, and would serve only to erode features.
Here's the 2D and 3D - boats are clearly visible. Some are left as depressions in the bottom - wood that has rotted away?

Scapa Flow:

Here a link about the wrecks in Scapaflow!
www.scapaflowwrecks.com/wrecks/dresden/3d/index.php

Cool!