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Thursday, December 20, 2007

Navigation Radar Overlay

If you know me, or you've been reading my columns and blog entries, you know I'm not a fan of the nav-radar overlay. The weather overlay's great, it's just the nav-radar I have issues with. I'm sure there are other mariners out there who think the nav-radar overly is the best thing since the invention of the paddle. I'm just not one of them. I find the image at best distracting and at worst misleading. It's even worse when you start adding AIS and ARPA capability. Too Much Information (TMI) on one screen for my taste -- or maybe it's my 54 year old brain that can't unravel the two-system imaging.

Look at the screen grab below as presented by an ICAN radar overlay. Everything is lined up perfectly where there is a bold shoreline or a bold target but at locations where there are softer targets the image, for obvious reasons, doesn't quite correspond. It's misleading. If you were looking at the radar on a dedicated screen, with no overlay, you would automatically reference a chart first to make sure you weren't creeping into shoal water, say toward the souther'd of the chart, where you see the darker blue or light green of what might be a bar. Also, if you look closely at the image, you'll notice a lot of sea clutter around the position of the boat. To be honest, I can't tell from this screen grab if it's true sea clutter or a bunch of contacts. Either way, if you were to add chart images of nav-data, buoys or day markers, you'd be looking at a lot of different colored imaging. Personally, I would rather have the two screens side by side on two separate and dedicated display units, without the distraction of multiple and confusing images. I could then verify ship's position with the radar, which, if installed and tuned properly, is considerably more accurate and trustworthy than the GPS-based electronic charting and tracking system. Let's face it, the GPS plotter is not 100% accurate, no matter how it's installed.
Here's another screen grab, this time from a MAXSEA overlay (below). Similar issue. Presumably, where the shore isn't bold, there's no radar return. Where the target is hard and, particularly where it has some height (inland) there is a good strong return. But how do we know we don't have a GPS accuracy issue at play here?

Granted, if we had GPS accuracy issues, we would have them with the overlay as well as without. In other words, the dedicated chart display would be similarly skewed by the incorrect GPS input data. Some might argue that having the overlay brings the GPS inaccuracy to the attention of a helmsman faster than if he or she had been staring at two dedicated displays. It's a valid point, but I would argue it instills a false sense of security and confidence. I would rather see my helmsman operating on the basis of not knowing for sure than assuming the position of the target is somewhere between the charted position and that of the radar image. It's too easy to make that visual leap of faith with an overlaid image.

Finally, I think the TMI issue is serious enough that electronics manufacturers have to dial back on the technology until such time as a study has been completed to determine if captains and mates are susceptible to information saturation. We already hear reports of captains and mates filtering out AIS data while in high traffic areas. To me, this is a clear indication that the radar/plotter display has reached an information saturation point.

Perhaps these overlay issues wouldn't bother me if I was looking at a large, high resolution screen. Or maybe if I had picture and spot zoom capability. I'm not sure. My gut feeling is we need more data processing and less data imaging. If things keep going the way they're going, we'll have three dimensional virtual displays of everything taking place outside of the wheelhouse windows. When that happens, somebody is bound to ask why we need real captains and crews. (See USV below.)


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