Having a little problem with my chart display showing my position approx 150
ft west of actual, I checked chart datum (NOAA BSB raster type) and found
it was NAD83, whereas my GPS (non-WAAS) had been set to WGS84. So just for
the heck of it I set the GPS to NAD83. That didn't correct the position
error. From what I understand, WGS84 and NAD83 are practically identical,
so is there any reason not to just leave GPS set to WGS84 (this is in SW
Florida, USA)?

Any advice on what else to check to correct the westerly error would be
appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

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Eliminate "ns" for email address.

Besides having the correct datum selected in your GPS, check the
longitude/latitude display settings. The difference between
degrees/minutes/seconds and degrees/minutes/tenths may account for the
discrepancy between your GPS and the Chart.

"Len Krauss" wrote in message
...
Having a little problem with my chart display showing my position approx
150
ft west of actual, I checked chart datum (NOAA BSB raster type) and found
it was NAD83, whereas my GPS (non-WAAS) had been set to WGS84. So just for
the heck of it I set the GPS to NAD83. That didn't correct the position
error. From what I understand, WGS84 and NAD83 are practically identical,
so is there any reason not to just leave GPS set to WGS84 (this is in SW
Florida, USA)?

Any advice on what else to check to correct the westerly error would be
appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

--
Eliminate "ns" for email address.

"Len Krauss" wrote in message
...
Having a little problem with my chart display showing my position approx
150
ft west of actual, I checked chart datum (NOAA BSB raster type) and found
it was NAD83, whereas my GPS (non-WAAS) had been set to WGS84. So just for
the heck of it I set the GPS to NAD83. That didn't correct the position
error. From what I understand, WGS84 and NAD83 are practically identical,
so is there any reason not to just leave GPS set to WGS84 (this is in SW
Florida, USA)?

Any advice on what else to check to correct the westerly error would be
appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

My Garmin 182C with the latest Blue Chip puts my boat exactly where it
should be in my marina. Right on the correct finger.
I recently bought Ozi Explorer and a friend gave me a set of older charts on
CD. With this set-up my boat is 150 yards too far North-East. I thought it
might be the datums but no other datum gave better results than WGS4. I
bought the latest paper chart for the area and plotted the L/L shown on the
laptop. Exactly correct on the new chart. So the old chart on the CD was
inaccurate by 150 yards in terms of the location of my marina. I imagine it
is more accurate for navigational hazards but it makes you wonder.

GPS's are great, aren't they?
My GPS 198C put me right in a slip. When tied up, the only difference was
that the GPS indicated I was on the right side when I was centered in a two
boat slip.
The key is to avoid constant heading/speed changes, so the GPS can keep up
with your progress.
Quite a confidence builder.
But, we'll never be without a paper chart on my boat, and the radar's always
on and a lookout posted. Even on nice, sunny days.


"Gordon Wedman" wrote in message
news:WtoIf.1208$n67.820@edtnps89...

"Len Krauss" wrote in message
...
Having a little problem with my chart display showing my position approx
150
ft west of actual, I checked chart datum (NOAA BSB raster type) and
found
it was NAD83, whereas my GPS (non-WAAS) had been set to WGS84. So just
for
the heck of it I set the GPS to NAD83. That didn't correct the position
error. From what I understand, WGS84 and NAD83 are practically
identical,
so is there any reason not to just leave GPS set to WGS84 (this is in SW
Florida, USA)?

Any advice on what else to check to correct the westerly error would be
appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

My Garmin 182C with the latest Blue Chip puts my boat exactly where it
should be in my marina. Right on the correct finger.
I recently bought Ozi Explorer and a friend gave me a set of older charts
on CD. With this set-up my boat is 150 yards too far North-East. I
thought it might be the datums but no other datum gave better results than
WGS4. I bought the latest paper chart for the area and plotted the L/L
shown on the laptop. Exactly correct on the new chart. So the old chart
on the CD was inaccurate by 150 yards in terms of the location of my
marina. I imagine it is more accurate for navigational hazards but it
makes you wonder.

Len Krauss wrote:
Having a little problem with my chart display showing my position
approx 150 ft west of actual, I checked chart datum (NOAA BSB raster
type) and found it was NAD83, whereas my GPS (non-WAAS) had been set
to WGS84. So just for the heck of it I set the GPS to NAD83. That
didn't correct the position error. From what I understand, WGS84 and
NAD83 are practically identical, so is there any reason not to just
leave GPS set to WGS84 (this is in SW Florida, USA)?

Any advice on what else to check to correct the westerly error would
be appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

It's your calibration data that is off by 150ft. Re-calibrate (if your
program allows it!)

Huh?
"Dennis Pogson" wrote in message
news
Len Krauss wrote:
Having a little problem with my chart display showing my position
approx 150 ft west of actual, I checked chart datum (NOAA BSB raster
type) and found it was NAD83, whereas my GPS (non-WAAS) had been set
to WGS84. So just for the heck of it I set the GPS to NAD83. That
didn't correct the position error. From what I understand, WGS84 and
NAD83 are practically identical, so is there any reason not to just
leave GPS set to WGS84 (this is in SW Florida, USA)?

Any advice on what else to check to correct the westerly error would
be appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

It's your calibration data that is off by 150ft. Re-calibrate (if your
program allows it!)

I think you can scan a paper chart or topo map and then upload to some nav
programs. If you do this you have to calibrate the map by telling the
software what L/L is represented by points selected on the chart. I don't
think the original poster is likely to be doing this.
I'm not aware of any calibration being necessary if you up load commercially
produced charts. I believe the calibration data is part of the chart data.

"William Andersen" wrote in message
news:LhUIf.81$xH.38@dukeread03...
Huh?
"Dennis Pogson" wrote in message
news
Len Krauss wrote:
Having a little problem with my chart display showing my position
approx 150 ft west of actual, I checked chart datum (NOAA BSB raster
type) and found it was NAD83, whereas my GPS (non-WAAS) had been set
to WGS84. So just for the heck of it I set the GPS to NAD83. That
didn't correct the position error. From what I understand, WGS84 and
NAD83 are practically identical, so is there any reason not to just
leave GPS set to WGS84 (this is in SW Florida, USA)?

Any advice on what else to check to correct the westerly error would
be appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

It's your calibration data that is off by 150ft. Re-calibrate (if your
program allows it!)

Oh, thanks.
"Gordon Wedman" wrote in message
news:XQ2Jf.1383$Y22.664@clgrps12...
I think you can scan a paper chart or topo map and then upload to some nav
programs. If you do this you have to calibrate the map by telling the
software what L/L is represented by points selected on the chart. I don't
think the original poster is likely to be doing this.
I'm not aware of any calibration being necessary if you up load
commercially produced charts. I believe the calibration data is part of
the chart data.

"William Andersen" wrote in message
news:LhUIf.81$xH.38@dukeread03...
Huh?
"Dennis Pogson" wrote in message
news
Len Krauss wrote:
Having a little problem with my chart display showing my position
approx 150 ft west of actual, I checked chart datum (NOAA BSB raster
type) and found it was NAD83, whereas my GPS (non-WAAS) had been set
to WGS84. So just for the heck of it I set the GPS to NAD83. That
didn't correct the position error. From what I understand, WGS84 and
NAD83 are practically identical, so is there any reason not to just
leave GPS set to WGS84 (this is in SW Florida, USA)?

Any advice on what else to check to correct the westerly error would
be appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

It's your calibration data that is off by 150ft. Re-calibrate (if your
program allows it!)

William Andersen wrote:
Oh, thanks.
"Gordon Wedman" wrote in message
news:XQ2Jf.1383$Y22.664@clgrps12...
I think you can scan a paper chart or topo map and then upload to
some nav programs. If you do this you have to calibrate the map by
telling the software what L/L is represented by points selected on
the chart. I don't think the original poster is likely to be doing
this.
I'm not aware of any calibration being necessary if you up load
commercially produced charts. I believe the calibration data is
part of the chart data.


Len is keeping very quiet since his original posting. Has he found something
embarrassing, and doesn't wish to tell us?

No, Dennis, nothing embarrassing found. Was just waiting for more input from
everyone.

I was beginning to wonder if magnetic variation could possibly have
something to do with the position discrepancy. My GPS is set to
automatically adjust for it. I've downloaded for my Capn software the latest
magnetic variation data table. I concluded, however, that variation would
only influence magnetic heading displayed, and not lat/lon. In other words,
it has nothing to do with the problem. Does that sound right?

The only other thing I can think of is that chart datum and GPS datum need
to be in agreement. Chart is NAD83 and with GPS set to NAD83, position
error unchanged. Same with GPS set to WGS84. Datum is the only kind of
"calibration" possible, as far as I know.

Len


--
Eliminate "ns" for email address.

Len is keeping very quiet since his original posting. Has he found
something
embarrassing, and doesn't wish to tell us?