Plotting a course on a GPS

[drevil]

I was reading another thread and the comment was made someone to get a paper map and use it to plot a course on your GPS.

My question is, with the maps that I have seen, there are not many GPS points to use as a reference. How do you plot a course on a GPS if the map has no GPS coordinates and you don't have any mapping software on the GPS?

Apart from actually going out there and punching in waypoints as you go using visual markers as a guide to whether you are on course or not, I'm not sure how this would be done.

[blaze]

hi
down the sides and along the bottom and top of a map is a series of numbers and increments, they will translate directly with a gps co-ordanate, as long as the map uses the same datum as your gps. Sit down with the map and work out the marks (gps spots) and then punch them into your gps and turn them into a route
confusing, yes,
also buy a book on basic map navigation, that will make iy all seem easier
cheers
blaze

[SeaHunt]

Drevil, the proper maritime charts put out by Queensland transport have the Latitude and Longtitude numbers across the top and down the sides and to wdg 84 or whatever it is , same as GPS.

[drevil]

Thanks guys, I'll check it out.

[Needmorerum]

Stupid question, which is latitude and which is longtitude. Can never remember which way they go.

Corry

[clutter]

Latitude - laterial - sideways - horizontal on the map.
Longitude - up and down - top to bottom - vertical.

Cutter

[Morlers]

Longitude lines run from North Pole to South Pole and measure degrees East/West of Grenwich (or zero degrees), Latitude lines run around the Earth parallel with Equator and measure degrees South or North of Equator.

Therefore it is say 24deg45.450min South Latitude and 152deg24.300min East Longitude for Burnett Heads Marina (approx).

Hope that helps.


Morlers

[Cheech]

Drevil,,,, another tip if you want to try to improve the accuracy of the spot..

If the marks on the map between each major point with a line down or across... eg between 152deg 24.000 minutes, and 152deg 25.000 minutes is too small or difficult to work out where inbetween you are, then it can help to blow up the map or section of the map on a photocopier.

Then all you need to do is measure the distance between 24.000 and 25.000, and then measure the distance between 24.000 and your spot. Divide the longer measurement by the shorter measurement and you will have the exact gps mark.

as an example, if the distance between 24 and 25 is say 143mm and the distance between 24 and your spot is say 87mm then divide 87 by 143 and you will get 0.60839 so your coordinate is 152.24.608

Even if you don't need to blow up the map, this same procedure will work the same.

Cheech

[webby]

Cheech you have to do a few more calculations to get it right doing it that way.
Latitude as you no round around the earth and are a fixed distance apart.
Longitude run north south, but only at the equator are they the same distance apart, as the line run north and south the narrow in to the poles.
But for areas like the bay, there is not that significant a difference on the longitude line, but if working out a fixed point off a maps further north or south difference will start to appear.
regards,

[bigbrian47]

there was a bloke on bribie that printed a clear
gps user aid
you place the aid over your map to get accurate
marks in degrees/minutes seconds
i bought mine years ago @ still have it
cheers brian

[drevil]

My brain is starting to hurt

[CHRIS_aka_GWH]

topics like this make you appreciate the skills involved in our navigating forebears.

Maps, compass, stars & ropes with knots in them - I'm in awe of what they used to achieve on the open ocean.

[Splash]

there was a bloke on bribie that printed a clear
gps user aid
you place the aid over your map to get accurate
marks in degrees/minutes seconds
i bought mine years ago @ still have it
cheers brian

Anyone know where i can get this aid from?

Splash

[Noelm]

most TAFEs do a coastal navigation course, and if you have to proper charts and do the local compass deviations/variations, then used in conjuction with your GPS it is very easy to plot a course, the chart is used as a ready way to actually see if what your GPS is telling you in relation to where you are going, remember that your GPS does not tell you about land or reef, so unless you are just doing a fishing trip and want to just find a "spot" then a chart is needed for long trips, in the 'old days" a hand held compass was used to get a "fix" on known points of land to get your 3 way location from from land points, and then lines are drawn on your chart to "triangulate" your location, a GPS does away with this task, but a GPS is "true" lat and long, your charts are not and vary over time, but it is all on your chart.

[Noelm]

I forgot to add, when you plot a course an acurate watch/clock is also a good (necessary)item to have, what you do is you mark your location on the chart (from your GPS) then you take your heading and draw a line on the chart, from your speed and heading you mark a point the distance away that you should be according to your present course and speed, in unknown waters you would do this every (say) 1/2 hour, then at the half hour, you again take a GPS "fix" and relate it to your previously marked spot, it must be on or very close to it, if not you make a slight course correction so next half hour fix, it is on the drawn line and on the marked spot, get the idea?