Ripping Maps?

[deepthought]

Just wondering I see lots of people ripping maps from google earth or msn whatever for opencpn what is the difference between that and garmin or navionics or one of the others?

[transmitterdan]

Charts made from GE or other satellite data do not contain depth, bridge type and clearance along with a host of other information found on hydrographic charts. They are not navigation charts but rather just geo referenced photographs.

In a few cases such as South Pacific islands the GE satellite images may (or may not) be more accurate regarding shoreline locations. But they only show what the satellite sees. Nothing more.

[deepthought]

Sorry yes I know the difference in that way but I meant more on a legality standpoint?

I see lots of people share there GE kaps etc.. for opencpn but I do not see other navigation charts shared.

[Ambler]

Google Earth is free so sharing is fine.

Other charts are copyright so who would openly share those?

Actually selling photocopied charts like the photocopy shop does in Whangarei NZ would have to attract heavy fines surely. But they have been doing it for years apparently.

Swapping charts has been the tradition ever since yachts first sailed over the horizon. If they are used paid for originals that is OK.

The key to ANY chart received be it paper or electronic, is to understand its limitations!

[SailingFan]

Yes, and you additionally have to remember that it is what those satellite photos do NOT show that will sink your vessel. The photos are really not that useful, because they don't show the depth (as already discussed), the currents (those change to a degree over time), the tides, where most wrecks are and how close to the surface they extend, the cable lines, the dredge dumps, the bridge clearances (already mentioned), the markers and the colors that these display, where reefs are and at what depth they become hazardous, or even what the distances are between one landmark point and another (try using a photo of above at night against channel markers and a lit shoreline in the dark), though I have solved that to an extent with a grease pencil and a gauge that is calibrated to the image with known examples of prior image scales.

In short, they have no real value I can use in navigating any area that would hold the information that the photos do have available for the reader to see. This is from someone who once used traditional weather, Keyhole, and DMSP satellites on a daily basis to do my job, and we occasionally got pretty close to surface imagery (especially with the Keyhole shots). Even the IR satellites got us little of use to navigation, other than the present position of the Gulf Stream and her eddies for instance.

It is essentially the concept of the right tool for the job at hand, and those pics are not the right tool for anyone attempting to sail a boat someplace. They can, however, get you placed onto a reef or a shoal pretty solidly if you are traveling at hull speed at the time of grounding, so if the goal is to kill the vessel, then yea, they will be just fine.

[conachair]

Originally Posted by SailingFan

Yes, and you additionally have to remember that it is what those satellite photos do NOT show that will sink your vessel. The photos are really not that useful, because they don't show the depth (as already discussed), the currents (those change to a degree over time), the tides, where most wrecks are and how close to the surface they extend, the cable lines, the dredge dumps, the bridge clearances (already mentioned), the markers and the colors that these display, where reefs are and at what depth they become hazardous, or even what the distances are between one landmark point and another (try using a photo of above at night against channel markers and a lit shoreline in the dark), though I have solved that to an extent with a grease pencil and a gauge that is calibrated to the image with known examples of prior image scales.

In short, they have no real value I can use in navigating any area that would hold the information that the photos do have available for the reader to see. This is from someone who once used traditional weather, Keyhole, and DMSP satellites on a daily basis to do my job, and we occasionally got pretty close to surface imagery (especially with the Keyhole shots). Even the IR satellites got us little of use to navigation, other than the present position of the Gulf Stream and her eddies for instance.

It is essentially the concept of the right tool for the job at hand, and those pics are not the right tool for anyone attempting to sail a boat someplace. They can, however, get you placed onto a reef or a shoal pretty solidly if you are traveling at hull speed at the time of grounding, so if the goal is to kill the vessel, then yea, they will be just fine.

On a scale of 1 - 5..... strongly disagree!

As an addition source of information google satellite images are a great free resource. They always seem to have been taken near low water so check where the channels really are ( or were when the image was taken anyway) and see how accurate the nautical charts are , cruising so many are based on very old data. See where the rest of the boats are anchored, where to get ashore. Lot's of useful info in addition to proper charts. Offshore as well, check for sea mounts zoomed right out which won't show up on vector charts.
Moving to a new cruising area a load of satellite images is very high on the list, easy these days with the excellent venture further Opencpn plug and Ge2Kap program.
What you say all makes sense thinking about it from ashore, day to day sailing it's throwing a valuable resource away for no reason, better to look at everything and anything you can get your hands on.

[Ambler]

Thanks SailingFan, One day you will get to Fiji where any and all charts are extremely inaccurate, then along with your dodgey chart of Fiji you will also consult a GE2KAP to scan along your proposed route for coral reefs and any other discolouration. You will also want a ratline ladder to the spreaders and a crew aloft with polarising sunnies.
All the tools in the shed before proceeding will get the job done by sunset!

[SailingFan]

Guys, when I get to the point I am heading to Fiji and the most remote islands of the Pacific, I will see what sorts of tools I can gather, because I am noplace near the Pacific right now.

I can see how the google earth pics could show some near surface features in some waters that are clear enough, but you have also to know when the pic was taken. I have seen some of those pics that were months or even years old. In the areas I am, shoals move every tropical season, and often more rapidly than that. Maybe it is a difference in locale. Maybe those pics are of use in waters I have not encountered, but I for one don't want to trust something I have already seen to be problematic.

Now I also know that paper charts are not always so great, and admit that I too have seen some issues with them. I agree that someone watching from forward and even higher up forward is going to be of benefit in any area, and we did that when in waters that are thinner. I would rely on that before a google map photo.

As far as sea mounts go, I am of varied thoughts on that. I recently read in these forums of someone finding a sea mount in the middle of the Atlantic someplace that was able to sink a vessel at low tide while not being apparent otherwise. That sort of event could be located on a satellite shot that was zoomed in, provided you had the precise location to search. Not sure it would be so helpful to see it though, there is a huge ocean to navigate around, so you could just skip that area entirely.

Additionally, if you looked at bottom topography maps, most of those mounts and reefs would be present, or at least the suggestions of them would be there. In preparation for your trip, those maps are also available online for little to nothing, so could inform your locations to check. They are relatively current in shallow areas compared to the maps we are already discussing, and in combination with satellite imagery I can see that they could be useful.

I do agree that if you have multiple sources, you should compare them and see what comes out of it. However, I would still be reluctant to use only google earth shots to attempt to navigate. If using them, I would use them in conjuction with other charting to see if what the chart says can be demonstrated in the image. If such was the case great, if not, I would definitely be more alerted when in those areas.

I do think that the weather images, especially the IR versions, were damned useful, and I can see there is a dual use for them, so any dual use thing on a boat is generally of increased value!

[transmitterdan]

Originally Posted by deepthought

Sorry yes I know the difference in that way but I meant more on a legality standpoint?

I see lots of people share there GE kaps etc.. for opencpn but I do not see other navigation charts shared.

Garmin and Navionics chart cards can't be "shared". They are copy protected so they can be sold or given away but not copied and shared. The official charts for many countries are free and OpenCPN will download and install the latest versions for most countries. Other countries make their electronic charts available for opencpn for a fee through online sale.

Today, all paid for charts include some type of copy protection that prevents "sharing". There are old, out of date charts without copy protection that are often shared by cruisers. Beware of these if found on the Internet as they are often used to lure unsuspecting souls onto virus infested web sites.

When someone shares GE "maps" they are not doing anything you cannot do yourself. The tools to "rip" google earth images are freely available. Google ge2kap for one. There are several others. Read Google Earth's terms of use for legality issues.

[conachair]

Another very useful source of data is to create a chart from the marine traffic density display'

GE2Kap instructions here ->
GE2KAP Help

Marine traffic window has a cursor lat/long onscreen to get some calibration points but doubt if I'll get better than within a mile or so, not that it matters much in this case.

Then if all is well you get something like this..

Kap file attached, just remove the ".doc"

Wonder if it's illegal....



StVincentDensity.kap.doc