Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-04-2013, 21:13   #1
Registered User

Join Date: Apr 2013
Posts: 2
What is a Simple Mercator?

according to georef.cpp, toSM()/fromSM(), which is used as enc projection. It looks like a common mercator, but takes into account the latitude of natural origin which seems to be the enc cell center.
So, what the major difference and benfit between the Simple Mercator and common mercator. Will it distorts features cross cells?
__________________

__________________
feverzsj is offline   Reply With Quote
Old 25-04-2013, 21:20   #2
Registered User
 
boat_alexandra's Avatar

Join Date: Aug 2009
Location: chesapeake bay
Boat: bristol 27
Posts: 2,816
Re: What is a Simple Mercator?

I think taking the latitude of origin is only to render on the right offset. Regular mercator charts can be overlayed at any time and align correctly, so it is common mercator. There is not distortion.

I could be wrong, but I believe simple mercator means it is using spherical coodinates rather than elliptical.
__________________

__________________
boat_alexandra is online now   Reply With Quote
Old 25-04-2013, 22:27   #3
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,884
Re: What is a Simple Mercator?

feverzsj...

boat-alexander is correct. SM uses spherical calculations with no eccentricity or elliptical correction terms. Read the code and you will notice the performance penalty incurred when calculating the correction terms.

We do a lot of this calculation in OpenCPN.....

Dave
__________________
bdbcat is offline   Reply With Quote
Old 25-04-2013, 23:10   #4
Registered User

Join Date: Apr 2013
Posts: 2
Re: What is a Simple Mercator?

Thanks for the replying!
So, this projection is Spherical Mercator which references lat0/lon0?
But, why a fixed scale factor 0.9996 is applied?
Furthermore, each cell now reference different point, won't that be a problem?
__________________
feverzsj is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 21:54.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.