MBnavadjust — navigation adjustment of swath surveys

MB-System's mbnavadjust, ported into iGMT. It makes the bathymetry of overlapping and crossing swath lines agree by adjusting their navigation. Each file of a project is cut into sections. Where two sections overlap they form a crossing, and at each crossing an offset, a tie, is set by hand (dragging one section's contours over the other's) or by correlation (Auto-Pick). An inversion turns all the ties into a smooth navigation adjustment for every file, which mbprocess then applies when it makes the processed files.

Workflow

1. File ▸ New creates a project: a .nvh file and a .dir data folder beside it. File ▸ Open reopens one.
2. File ▸ Import Swath Data adds swath files, or a datalist (MBIO format id -1), each file a survey of its own. Import Swath Data as Single Survey makes them one survey. The files are cut into sections (Option ▸ Controls: section length and number of soundings), the crossings are found, and the project grids are made with mbgrid.
3. The List menu chooses what the list shows: data files, surveys, blocks, sections, crossings (all, or by overlap), ties, global ties, reference grids. The View menu chooses which of them.
4. Selecting a crossing, or Action ▸ Analyze Crossings, opens the analysis window. On the right are the two sections' contours: drag with the left button to move section 2 over section 1, drag with the middle button to zoom, click the right button to pick the tie points. On the left are the misfit of every offset (click to set it; Minimum Misfit jumps to the best one) and the misfit against the z offset. Add Tie / Set Offset store the tie, Skip Crossing leaves the crossing out, Next Unset moves on. Settings holds the heading and roll biases and the contouring. Action ▸ Auto-Pick Offsets does all this by correlation for every unset crossing listed.
5. Action ▸ Invert Navigation solves for the adjustment (Option ▸ Controls: Inversion Smoothing). Update Grids applies it to the sections and grids them again. Apply Adjusted Navigation writes each file's adjusted navigation and sets it in the file's mbprocess parameters, as primary, secondary or tertiary navigation (Option ▸ Controls).
6. View ▸ Show Modelplot plots the adjustment model as a time series, as a perturbation, or the tie offsets.
7. View ▸ Visualize Survey opens the project grid in a viewer window with every section's navigation and every tie drawn on it. Click a tie to analyse its crossing, or click two sections one after the other to open their crossing. View ▸ Add and Open New Crossing makes one where none was found.

Closing or minimising the window parks it in Scene Objects. File ▸ Quit saves the project and closes the tool. Help ▸ How to use MBnavadjust (F1) holds the same guide.

How it is ported

• MB-System's GUI-free core (mbnavadjust_io.c, _autopick.c, _invertnav.c) is carried as it is.
• The engine (mbnavadjust_prog.c) and the Motif callbacks (mbnavadjust_callbacks.c) stay C. The callbacks run on a small widget bridge (mbna_motif.h): each widget is its Motif name, which is its objectName in the .ui files. The Qt window carries out the widget calls and draws the xg graphics into images.
• The pieces of libmbaux it needs (the swath contourer, the Delaunay triangulator, LSQR) are in mbna_aux.c. MB-System's grid reader keeps its own logic (mbna_grid.c); the grid values come from iGMT's grid reader.
• The programs upstream runs through system() (mbdatalist, mbprocess, mbgrid) run in iGMT as MB-System's GMT modules, in the project folder.
• The visualization, libmbview upstream, is an iGMT viewer window.