GPS Course calulator
The Real Andy
of the program I am writing. I am about to give it another test this
weekend. No sailing, but I am going to set a course then take
waypoints my chartplotter to verify the accuracy of the course angles
and size.
Sceenshots here:
http://www.syc.org.au/Racing/RacingSoftware/tabid/126/Default.aspx
When I get more time I will make the website look a little more
glamorous!
Jason Keats
0.049410799734416 nm implies you know your position to within a fraction
of a sub-atomic particle.
I'm pretty sure that three decimal places is more than enough precision.
The Real Andy
The GPS is not that accurate, its like that because I have just dumped
the raw output of the calulation to a label. There is lots that needs
to be done yet. The purpose at this stage is to simply test the
theory. Once that is done I will go through it at make it more
correct.
What you cant see is that when you enter the wind angle its going to
be magnetic north, where as the GPS is true north. The GPS has a
magnetic variation but it seems to always output 0. I dont know how it
would calulate magnetic variations though. Anyway, I will add someway
of correcting magnetic variations to the end product.
Jason Keats
>> I'm pretty sure that three decimal places is more than enough precision.
>
> The GPS is not that accurate, its like that because I have just dumped
> the raw output of the calulation to a label. There is lots that needs
> to be done yet. The purpose at this stage is to simply test the
> theory. Once that is done I will go through it at make it more
> correct.
>
> What you cant see is that when you enter the wind angle its going to
> be magnetic north, where as the GPS is true north. The GPS has a
> magnetic variation but it seems to always output 0. I dont know how it
> would calulate magnetic variations though. Anyway, I will add someway
> of correcting magnetic variations to the end product.
I understand it's a work in progress. But that's no excuse. <g>
I think most people (who use a chart) would know the local variation -
it's only one number to enter and save.
You won't be going to the trouble of looking up (or calculating)
variation based on lat/long and date will you? That'd be a bit hard, and
unnecessary.
Anyway, your program looks good. Let us know how it performs.
The Real Andy
<jke...@melbpcDeleteThis.org.au> wrote:
>The Real Andy wrote:
>>> I'm pretty sure that three decimal places is more than enough precision.
>>
>> The GPS is not that accurate, its like that because I have just dumped
>> the raw output of the calulation to a label. There is lots that needs
>> to be done yet. The purpose at this stage is to simply test the
>> theory. Once that is done I will go through it at make it more
>> correct.
>>
>> What you cant see is that when you enter the wind angle its going to
>> be magnetic north, where as the GPS is true north. The GPS has a
>> magnetic variation but it seems to always output 0. I dont know how it
>> would calulate magnetic variations though. Anyway, I will add someway
>> of correcting magnetic variations to the end product.
>
>I understand it's a work in progress. But that's no excuse. <g>
Fixed now, down to 2 digits! No screen shots yet though. Also fixed up
heaps of other stuff today. The heading compass now has a lubber line
and roates the rose, rather than a fixed rose with a needle. Changed
some text fields, fixeds some bugs, named the main form so its not
called Form1...
>
>I think most people (who use a chart) would know the local variation -
>it's only one number to enter and save.
>
>You won't be going to the trouble of looking up (or calculating)
>variation based on lat/long and date will you? That'd be a bit hard, and
>unnecessary.
Well I am not sure how the GPS works exactly, but the NMEA protocol
has a field called Magnetic Variation wich is supposed to give the
magnetic devation, or so all the internet doco says. The NMEA protocol
costs about $300USD so I am not going to buy it. The GPS I have (route
66 brand) always outputs 0.
From what I can gather from reading google the GPS has an almanac
built in (I always though it got that from the satellite) which can
give you the magnetic deviation. I need to read up more on this, but
suffice to say that my GPS obviously does not support this feature. I
will add in a an option to the setup to cater for magnetic devation. I
doubt the app will ever get used over such a distance where magnatic
deviation will vary. If it does it will be a problem anyway because I
am usign a constant for the earths circumference! Not an issue for a 1
or 2 nautical mile course!
>
>Anyway, your program looks good. Let us know how it performs.
If the weather is good tomorrow I will take it out and do some
testing. My initial test done walking around the city showed up a few
bugs, hopefully that is all resolved now.
The Real Andy
Spent a few hours out on the water on Saturday laying courses (no
sailing) and I can say that this is going to make my life much easier.
Few small issues, first one being that the course legs were not
correct distances. I forgot to use the multiplier (0.7) for
calulating the reaching legs. My initial tests of the GPS math used
them, but I forgot to add to my program. It now uses correct trig
functions rather than constants anyway.
Second issue was the navigation display that shows you to the next
mark. I had a fixed compass rose with a needle pointing to the bearing
you need to follow. It does not work and is hard to use. I have now
changed it so the rose rotates as a real compass would, and the needle
points in the direction you need to travel. IE, the needle shows the
heading relative to the bow of the boat.