Grid Ref using Garmin 200W

sesswhat

Unlike hand held GPS devices for outdoor pursuits, many car satnavs don't give you the option of displaying your location using local grid co-ordinates, for example Irish Grid. Of course for most people this isn't a problem.

I was playing around with ways to plot your position if you were out and about with your satnav and an Ordnance Survey map.

The OS maps have Lat and Long markings in degree minutes around the edge. If you took the readings from your satnav in the format 'dd mm.mmmm' these markings could be used to get a rough fix. It would be quite awkward though, involving a bit of ruler and pencil work for any kind of accuracy.

With a 100 metre Grid Reference like H 131 901 it's obviously quite easy to use the 1km gridlines on a 1:50,000 map to estimate your position. To get a 100m grid ref from my Garmin nuvi 200W, I did the following:

Each grid letter denotes a 100km by 100km square. With a bit of programming, I started 50m from the bottom left corner of grid square 'O', and converted points at 100m intervals along the left edge into custom POIs. Each POI was named in sequence according to the 100m square it represented. I copied them into a file named 'O_100m_north.csv'. I did the same for the bottom edge and called the file 'O_100m_east.csv'.

I put both files into a folder called 'Grid_O' and loaded these 2000 POIs into the Garmin.

To get a grid reading within this Grid Square, I now selected 'Where to?' > 'Extras' > 'Custom POIs' > 'Grid_O'



Choosing the east category first, the unit will list the closest POI first, which should be the one directly South of the current position:



Take note of the result then click back and choose the north category. The top result this time should be directly West.



You now have a full Irish Grid Reference O 159 346 (in this case for the Spire in Dublin) for the 100m square you are in.

As you would expect, the distance reading from the relevant POI in kilometres (x 10) is close enough to what the other reading should be. However, maybe due to rounding errors, I found it to be more accurate to reference both the eastings and northings.

This example uses one set of POIs but of course you could apply the same system to any Grid square or any similar grid system. I experimented with POIs in two intersecting lines to cover the whole country, but as the distances get greater, the accuracy breaks down and you have to use bigger intervals.

I don't know if anyone is interested in trying it, but if so, I can post up the files for your Grid Square.

eirlink

interesting...
how did you capture the screenshots?

sesswhat

There's a built-in mechanism.

Tools > Settings > Display > Screen Shot (Set to enabled)

A little camera appears on screen which you can click to capture a screen shot.

When you hook it up to your computer you can find them stored as .bmp files in a folder called something like 'scrn'.

pmsurveys

I use garmin mobile xt on my phone as well as others including TT730 and co-pilot on a pda but on my garmin if I highlight the satellite signal strength icon the display shows locations etc of satellites and if i click this then I get a display showing co-ordinates based on grid system I selected in the settings. Irish Grid is not there but I wouldnt expect it to be as it has been abandoned since 2002 but ITM is there and works great. I dont know if these settings are available on the garmin units but would be interested to know if they are.

sesswhat

Irish Grid and/or ITM can usually be found on the hand held units for trekking and marine use, as well as multi-use units like the nuvi 550. However, the choice on the cheaper car units like the 200w may be various formats of Lat Lon only.

Even though ITM is being pushed to replace Irish Grid for commercial applications, I imagine the Irish Grid system will be used by the wider public for a long while to come, especially those who have invested in popular printed maps like the 1:50,000 series.

pmsurveys

sesswhat wrote: »

Irish Grid and/or ITM can usually be found on the hand held units for trekking and marine use, as well as multi-use units like the nuvi 550. However, the choice on the cheaper car units like the 200w may be various formats of Lat Lon only.

Even though ITM is being pushed to replace Irish Grid for commercial applications, I imagine the Irish Grid system will be used by the wider public for a long while to come, especially those who have invested in popular printed maps like the 1:50,000 series.

Maybe so ..... but the Land Reg have already changed and compulsory registration is planned for 2010 so by then everyone should be more aware and using a more accurate system anyway.

Diarmuid0000

sesswhat wrote: »

I don't know if anyone is interested in trying it, but if so, I can post up the files for your Grid Square.

I am very interested. I spent hours on the internet trying to figure out exactly this. I would love the files for Grid N, O, S & T. Thanks.
PS I am new to boards.ie so apologies if I am doing this wrong!

coylemj

There is a free co-ordinate converter on the OSi website.

http://www.osi.ie/en/alist/co-ordinate-converter-tool.aspx

sesswhat

Diarmuid0000 wrote: »

I am very interested. I spent hours on the internet trying to figure out exactly this. I would love the files for Grid N, O, S & T. Thanks.
PS I am new to boards.ie so apologies if I am doing this wrong!

Forgot about this thread. I'll get those files uploaded later today.

I revised the system since the original post. The separate grid files were OK if you knew for certain what Grid square you were in. These new POI files cover the whole country - one file for eastings, one for northings.

Unzip the attached file and install the contents of the Custom POI folder to your device, or an SD card, using POI Loader. Don't forget to back up any existing Custom POIs you have first!

sesswhat

coylemj wrote: »

There is a free co-ordinate converter on the OSi website.

http://www.osi.ie/en/alist/co-ordinate-converter-tool.aspx

Obviously, if you have access to a computer in whatever remote spot you find yourself, you won't need all of this nonsense anyway. In that case, another good conversion site is Fielden Maps. This is javascript based, so if you save the page, you can use it offline as well.