CM93 Charts Up to Date ?

[tonydix]

I have just managed to get OpenCPN working and have been given a disk with I suspect very old CM93 charts which open correctly.
My question is how can I find out the date of these files and whether or not a more upto date series of charts is available.
Thanks for any help
Tony

[clarity36]

Tony
There are a host of valid copies of CM93 getting around, dated around mid 1990's and up to date till then. Not updateable. Good value if you use paper charts, with electronic as backup. Not so good if you rely on electronic navigation as your primary nav source. Read the agreement of every electronic nav package money can buy. They all state that you have to accept this is "an aid to navigation", not a valid nav source, and should not be relied on stand alone. Cheers. Bill

[Jon Hacking]

Originally Posted by tonydix

I have just managed to get OpenCPN working and have been given a disk with I suspect very old CM93 charts which open correctly. My question is how can I find out the date of these files and whether or not a more up-to date series of charts is available. Thanks for any help, Tony

Hi Tony - Welcome to Cruisers Forum!

To find the date of your CM93 charts in Windows, Open Windows Explorer (not IE) & navigate to wherever you stored the charts, usually C:\CM93. In that folder will be a bunch of other folders that are just numbers - open any folder. In there you will find a bunch of folders that are just letters - open a C folder. In there will be the actual chart files. Set your view to Details so you can see the dates of the files. Click on the "Date Modified" to sort on the date. The newest files will be the effective date of your CM93 chart database. You can check some other files in other folders to double check this. It does not work to just check the dates of the folders, as those will be the date that you created the folder (ie, when you installed the charts) but the files themselves usually keep their dates when they're copied.

We've seen CM93 charts dated 2000, 2002, 2005, 2006, 2008, 2009, & 2010. No doubt there are others that we haven't seen. The charts are surprisingly good, but have strange errors. All of Sri Lanka seemed to be spot on, EXCEPT the one port you could go into (Galle) which was out by 1/4nm until 2009! Tonga was ALL out by 1/4nm when we were there in 2004. Apparently the Philippines have errors of up to 2nm in places.

The charts are usually correct within themselves - their errors are that they're displaced from where they should be. OpenCPN has a lovely feature to correct this manually but you have to remember to turn that correction OFF when you leave that area.

When approaching a new area, it's always a question: How accurate are my charts? If your radar is tied into your GPS via NMEA, there's a couple of ways to test this. Turn on your radar & find a prominent headland or point that's not too far away. Put your cursor on that point to read off the Lat/Lon & compare that to your charts. This gives a good comparison between reality (GPS/Radar) & your charts.

[tonydix]

Many thanks guys your suggestion worked my files seem to be dated 1998 !!
Tony

[gravosa]

i have cm93 january 2011. it is spot on where i am sailing

[conachair]

Originally Posted by Jon Hacking

When approaching a new area, it's always a question: How accurate are my charts? If your radar is tied into your GPS via NMEA, there's a couple of ways to test this. Turn on your radar & find a prominent headland or point that's not too far away. Put your cursor on that point to read off the Lat/Lon & compare that to your charts. This gives a good comparison between reality (GPS/Radar) & your charts.

Agree they are generally very good, considering the price
Though out of the way I've sailed up streets before, Surinam comes to mind. Thinking back, google earth , from memory, seemed accurate even when the charts were out. Has anyone used the google earth plugin to check the accuracy of the chart datum of cm93 on opencpn?

Though when it gets to that I don't trust anything.

[Seachange2]

Originally Posted by gravosa

i have cm93 january 2011. it is spot on where i am sailing

Where did you get your CM93 charts, If you don't mind sharing?

Thanks

[Jon Hacking]

Originally Posted by conachair

... Thinking back, Google earth seemed accurate even when the charts were out. Has anyone used the Google earth plugin to check the accuracy of the chart datum of cm93 on OpenCPN?

We've now worked a bit with Google Maps & Google Earth, & from what we've seen they're spot-on accurate, much more so than the CM93 charts. We've been publishing Track Files in both MaxSea & OpenCPN format, & the converter we're using allows us to make a Google Map of the exact track, so folks can see exactly what they're downloading. GM shows all of our screw-ups very accurately

This makes the OpenCPN GE plugin that much more useful.

The charts are usually correct within themselves - their errors are that they're displaced from where they should be. OpenCPN has a lovely feature to correct this manually but you have to remember to turn that correction OFF when you leave that area.

I must amend my earlier statement. OpenCPN v2.5 now lets you adjust chart positioning on a chart-by-chart basis. The Help system tells you how, but basically you have to turn off Chart Quilting, adjust the chart, & then turn Chart Quilting back on again. This is MUCH better than adjusting your GPS to make it agree with the (flawed) charts.

It would be cool if someone had a list of offsets for various charts (with the date of those charts) & then shared that list. If folks are interested in this sort of thing, we'd be happy to provide the web-space. We have a (very small) list but we haven't been very far since v2.5 came out.