Originally Posted by SlugmasterP
I have a set of CM93 charts and they aren't detailed at all for the coast and bays. It's my understanding that they are vector charts? I'm not sure what those are but I'm guessing they are just for determining distance and eta etc? If anybody could explain the purpose of them to me I'd be grateful. I wouldn't feel comfortable entering an unknown bay using just a CM93 on OpenCPN
seems really hard to get electronic charts for as well. Is Navionics
the way to go? Thanks
Well, actually, the amount of detail and what they are for have nothing to do with the fact that they are vector charts.
Having little detail is due to one or both of the following.
1-CM93 charts are world wide, but have better coverage in some areas than in others. Some places they are dismal indeed.
2-If you don't have all the correct options checked in OpenCPN, you won't see all the details. Check in the OpenCPN subforum for answers on that.
Raster charts are simply scanned versions of paper charts. Bitmaps, basically. The charting software
just takes that image and positions it on the screen
where it should be geographically.
Vector charts are actually like a database. It is a list of features and where they are. The charting software
looks at each item and draws it on the screen
where it should be.
The advantages are that vector charts can show only the class of object(s) you want to see. When you zoom out, it can increase the size of the text to keep it readable. It can alarm
if you get to a place where the chart says it is too shallow. It can change the soundings from fathoms to feet. Some software even shows lights lit up only if they should be able to be seen from your current
location (taking into account the elevation of land between you and the light).
Vector charts also take up MUCH less disk space. This is one of the reasons that every stand-alone chartplotter
I know has vector charts built in instead of raster.
But, the fact that vector charts remain clear and sharp no matter what the zoom level can lead people to zoom in further than the chart is accurate. And many people are just familiar with reading paper charts and so are more comfortable with raster charts.
Here, you can read a short piece I wrote on chart errors and accuracy.
==> Inland Waters Resources - Chart Errors