Expedition Navigation Software 
1 of 1- Joe Goulet
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- From: Fort Lauderdale, FL USA
- Registered: 9/16/2015
- Posts: 83
Question Involving Dividers
Using Exp v10.2.18 and Windows 10 on three PCs, the latest being a year-old Surface Pro3.
Running the Race Sched module on the SDPV Race for practice (focusing on Class 3 in which I have friends racing) on the last of the NOAA RNC charts that I can use in this event (very small scale; San Diego to the Aleutian Islands and Hawaiian Islands 1:4860700), in the area of N30deg W117deg.. When I try to use the dividers to measure direction / distances between the various boats there is an offset (probably from 5 to 50 NM) in between the position where I click the cursor and the point where the end of the divider is drawn on the chart. This anomaly does not occur in using any other charts including the worldchart and I am questioning if it is associated with 1)Expedition processing Mercator projection distortions or 2)a possible problem with the RNC as issued by NOAA. Not a show stopper here, there are plenty of workarounds to use to obtain my info, but I am definitely interested in the origins of the anomaly.
- Nick
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- Registered: 9/16/2015
- Posts: 2,764
Re: Question Involving Dividers
Hello,
I can replicate that here. Almost certainly a small problem with the geo-referencing.
Update: I just had a close look at it and it is in the chart.
There are two ways geo-referencing is handled with BSB charts and the chart tells you which to use.
The first is it supplies some points and Exp works out the (eg) Mercator projection from that.
The other is the chart providers supplies some equations for the georeferencing and recommends using them. This is the case with this chart, so we know there is a small issue with the equations provided.
Fortunately it isn't a small scale chart you would use for anything critical, but it does highlight the need to be careful with electronic charts and that you are still required to use charts. Vestas.
The other option is the S-57 chart from NOAA, where the georeferencing is all handled by Exp, so you can't have this particular issue.
Nick
- Joe Goulet
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- From: Fort Lauderdale, FL USA
- Registered: 9/16/2015
- Posts: 83
Re: Question Involving Dividers
Wow! Thanks for the super-fast reply, Nick.
Your explanation nails my question. I never suspected that such an issue might exst with the old RNCs and I will take greater care to check them against the ENCs and be aware when they might be in conflict. I was initially a big fan of the move by Expedition to support S-57 and now I applaud it even more.
Similarly, I am a big proponent of recourse to the largest chart scales available when proximate to anything non-floating, electronic and paper.
Thanks again.
Last edited by Joe Goulet (2/20/2016 1:27 pm)
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