Treasure Coast/Space Coast BSB KAP MagTrakR and HDOP

[signumops]

I use MapTech on my laptop coupled with a Garmin 12 XL (no WAAS) as well as several other Garmin GPS units (with WAAS). I have found a way to update the BSB/KAP charts graphically for my own use. See the attached screen shot of a NOAA chart with the contractual boundary of the Cabin Wreck near Sebastian inlet. I have decided to update this particular chart further with all of the boundary files for the entire Fisher holdings as well as some other wreck boundary information. While I am at it, I might add other wreck locations that are fixed properly as the NOAA charts are frequently off by a mile or so in many instances, nor are the wrecks historically ID'd. In other words, this would be a third party compilation of some of the charts. If you use BSB/KAP in your own digital plotter, and you are interested in having your own waypoints/symbols added, I might trade you the finished product for your data.

Meanwhile, I have updated MagTrakR with a nominal GPS tracking processor. The NOAA charts are coarse when you are attempting to do something like track yourself while running a magnetometry pattern, so I use custom basemaps with MagTrakR in much higher resolution. Attached a screenshot of MagTrakR using its GPS processor. The pic was snatched from Google Earth... its a shot of my house where I was actually writing the code. I had the Garmin 12XL right about where the cross-circle symbol is shown. The upper left position is the marker set out in Google Earth which I used to geo-reference the photo in MagTrakR world space. The red crosses are the fixes posted from the GPS every 3 seconds or so for a few minutes. The GPS itself was situated near a porch overhang, under a SeaGrape tree, so I did not have a great collection of satellites to work with... I did not have enough serial cable to stretch outside of the house to optimize the GPS receiver position. As you can see, the HDOP (horizontal dilution of precision) was pretty bad as the signal meandered over a 60 foot area, about 50 feet from the true position of the GPS. This would not be the case if I were at sea with an unobstructed view of the satellites.

 

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[Hangingfor8]

I can see how it could be the big difference for the knowledgable salvor who's willing to put in the time to learn it and correctly use it. As we well know, alot of the old numbers are off, either by accident or to through other salvors off. Every big storm shakes the sandbox back up, but as they say.... "We'll never get it all"

 

[stevemc]

I do see a problem that can screw things up for people. The numbers on the chart with the houses, is in L/L Decimal/Decimal, and your numbers are in L/L Minutes, Seconds-as it should be. There can also be a L/L Minutes Decimal, which can also screw with the unknowing. I try to make sure all my #s are in L/L Minutes, Seconds, as that is how Charts (normal Nav charts) are numbered. What ever method you use, always use that method, as it can make things way off. I dont really know why anyone came up with the decimal method of charting. Why not just have it all the same? It makes it hard to chart on regular nav chart. EDIT! My bad the upper right corner box showing a LL is in L/L Minutes and decimals, while you spot # is in L/L decimal decimal, as I said a way to get all mixed up.

 

[signumops]

MagTrakR reads and reports in all three formats simultaneously. At any time you can change the metrics of the readout to sexigesimal, decimal minute, or decimal degree. The GPS tracking dialog is reading decimal minute, while the cursor position is shown in decimal degree. The extreme left hand lower box is displaying the raw foot distance from the equator and the Greenwich Meridian for the equivalent degree reading. For this screen shot I was fixing the photo using the decimal degree as was registered in Google Earth, which is why is am in decimal degree mode at the moment. MagTrakR figures all of this out on the fly.

Using decimal minute format, you know that every time the third digit after the decimal place changes a single digit, you have moved about 6.1 feet, either east-west or north-south (Longitude or Latitude). This figure changes as you move away from the equator, but here in Florida, 6.1 foot works.

Have you ever asked yourself why we commonly report in Latitude and Longitude rather than Longitude then Latitude? That's really confusing since, when in geometry class, we always express X before Y (Longitude before Latitude). Makes no sense.

Actually, mathematically, the decimal degree, using 8 decimal places can get you down to a foot distance while the decimal minute using 3 decimal places can only get you to within 10 feet. But, the standard GPS is only expected to get you to within 10 feet even on a good day. Imagine trying to read the 7th or 8th digit in a decimal degree to determine how far you moved... you'd go blind.