Help calibrating OSI Discovery map in OziExplorer for GPS use

pauln

Has anyone used an OSI Discovery map in Oziexplorer with a GPS unit. I'm having trouble calibrating the map image.

What Map Datum and Map Projection settings should I be using with OSI maps?

I know they've launched the trailmaster series but oziexplorer works better for what I want.

Alun

pauln wrote:

Has anyone used an OSI Discovery map in Oziexplorer with a GPS unit. I'm having trouble calibrating the map image.

What Map Datum and Map Projection settings should I be using with OSI maps?

I know they've launched the trailmaster series but oziexplorer works better for what I want.

It's pretty easy. I've done loads.

Map Datum : Ireland 1965
Map Projection : Irish Grid

I always use intersections of grid lines for my calibration points, but the trick in entering the values is to make sure you enter 5 digits for both the northing and easting. So for example, if you had a point that was on sheet T and a northing of 910 and an easting of 020 (for a normal 6 figure map reference) you'd enter 91000 and 02000 in the appropriate boxes (and T in the zone box, of course). I.e. always add two extra zeroes on the end of each figure.

For a scanned map, you'll want at least 3 points, preferably more if the scan was a bit wonky. BTW, it's well worth looking at the Mapmerge utility on the Ozi site if you're into scanning maps. It allows you to scan overlapping pieces of a larger map, calibrate the individual pieces and them merge them into one big map. Also the img2ozf utility will convert the maps into ozf format which are a lot quicker and cleaner to zoom, especially for larger maps.

Hope this helps. PM me if you need any more help, or want to trade maps etc.

pauln

That's great thanks I'll try that.

air

Hi there,
I'm trying to do this aswell with limited success. I've attached an image of ozi after I have loaded and calibrated a scanned map.
I have selected the correct quadrant and entered the points correctly but I'm pretty sure the displayed longitude and latitude is incorrect. I need to get a lead for my gps to confirm this though.
Also can someone tell me what the two numbers to the left of "Ireland 1965" signify? I expected them to be the northing and easting but while they increase / decrease by 1000 each when moving from one square to another as expected, the northing has too many digits and their offsets dont make any sense to me.
Any pointers appreciated.

Alun

That whole string to the right of the lat and lon is a UTM grid reference. Just right click on that area and you'll get a drop down menu which will allow you to choose Irish grid references instead.

I can't tell from the small screen shot where the map is you're calibrating, or where the cursor is, so I can't be of much help in saying whether the lat and lon are correct or not. If you can send me the .tif file and the .map file you generated I can have a look for you and see if I can see what you've done wrong if you like? I've done loads of these.

EDIT: Actually I think I know roughly where your map segment is, and if I enter the lat and lon you've got showing on your screen dump, then it looks like the cursor is a little south of the road crossing the map, so not far off. What makes you think the lat and lon you're seeing are wrong?

air

Hiya, thanks for the quick reply.
Cheers for the the info on clicking to change from UTM -> Irish Grid.
I've changed it and it's working spot on, all my irish grid references are perfect.
However my longitdue and latitude is definitely wrong. I have a web based GIS application that I use in work that plots points on google maps, the user enters the Irish national grid northing and easting and the application converts this to long & lat so that it can plot the site on google maps.
Anyway I entered a site based on Irish National grid co-ords from ozi and the site appears perfectly on google maps but the long and lat that are displayed in Ozi do not correspond with the true long and lat.

Alun

How far out is it? Just a small discrepancy, or nowhere near where it should be?

If it's just a small amount it's probably a datum thing. Ozi is showing the lat and lon according to the datum of the map which is Ireland 1965. If you want to display the lat and lon in WGS84, which is probably what Google Maps is showing, then just click on the 'Ireland 1965' on the status bar where the lat/lon/grid is displayed and it'll pop up a window where you can choose WGS84 instead. It only makes a second or two difference, but if that's the kind of difference you're seeing, it could explain it.

If the difference is much bigger then there's something else up.

Good luck!

air

Its out 15mins in longitude and 23mins in latitude so way out really!

Alun

air wrote:

Its out 15mins in longitude and 23mins in latitude so way out really!

That is a lot! I've seen strange things like this happen where one calibration point was entered wrong, say one down at the bottom of the map image. This has the effect that the displayed grid references at the other end of the map. e.g. the top, appear to be correct as you move the cursor around, but as you get closer to the incorrectly entered calibration point the error increases dramatically. You've effectively created a 'curved' map, if you see what I mean.

Maybe you should double check the calibration again? Otherwise my offer of checking it for you still stands, if you like. PM me if you want.

air

Well my perceived error didnt exist at all, I was simply comparing a longitude and latitude in DMS in one application with one in decimal notation in the other.
Many thanks to Alun for his help and great patience helping me out. Ozi is a great program!

ircoha

New to this section of boards.

I have a etrex vista and when I set it as follows:
Map Datum : Ireland 1965
Position Format: Irish Grid

I get the position displayed as
IO
and ITM

For example when it reads
IO 20680
ITM 45957

I am in square O2045 on the OSI grid

This I gather ties in with the OSI grid reference system as shown in the Dublin City 1:15,000 map.

My question is: will the http://www.oziexplorer.com/ map for Ireland show this grid system for the whole country, 26 counties at least.

Most OSI maps are at 1: 50,000, i need the 1:15,000 detail

If so what map am I after?
I gather that I need to get the OZI software and then either buy a digital map or scan from paper.


Can I link the etrex to a laptop and be able to show my position on the laptop using the OSI grid reference system?

I see in the OSI converter that they use
ETRF89 as the base for the lat/long portion.
the etrex only has WGS84.
What is the difference please?
Thanks

air

ircoha wrote: »

New to this section of boards.

I have a etrex vista and when I set it as follows:
Map Datum : Ireland 1965
Position Format: Irish Grid

I get the position displayed as
IO
and ITM

For example when it reads
IO 20680
ITM 45957

I am in square O2045 on the OSI grid

This I gather ties in with the OSI grid reference system as shown in the Dublin City 1:15,000 map.

My question is: will the http://www.oziexplorer.com/ map for Ireland show this grid system for the whole country, 26 counties at least.

Oziexplorer doesnt include any maps as you seem to understand below. If you calibrate a map correctly, yes it does support the Irish Grid properly.

ircoha wrote: »

Most OSI maps are at 1: 50,000, i need the 1:15,000 detail

If so what map am I after?
I gather that I need to get the OZI software and then either buy a digital map or scan from paper.

Just buy whatever map you would use normally for that scale and scan it.

ircoha wrote: »

Can I link the etrex to a laptop and be able to show my position on the laptop using the OSI grid reference system?

Yes, I've done this with an Etrex, works perfectly.

ircoha wrote: »

I see in the OSI converter that they use
ETRF89 as the base for the lat/long portion.
the etrex only has WGS84.
What is the difference please?
Thanks

Not sure tbh, if you calibrate the map you buy with the correct datum - the one from your map, it will work fine.

Alun

ircoha wrote: »

New to this section of boards.

I have a etrex vista and when I set it as follows:
Map Datum : Ireland 1965
Position Format: Irish Grid

I get the position displayed as
IO
and ITM

'ITM' is just the Garmin way of indicating that you're using the Irish Grid (Irish Transverse Equator). The I in IO you can ignore, the O is the grid square letter, UK ones consist of two letters, and someone at Garmin obviously thought Irish ones ought to too, so added the I. You can find out which grid square you're in by looking at the legend on the OS 1:50k series. it's also printed on the map itself at the intersection of the grid squares if applicable.

For example when it reads
IO 20680
ITM 45957

I am in square O2045 on the OSI grid

What you're seeing on the display is a full 10 digit (i.e. down to 1m) grid reference. No one uses that in real life, usually only a 6 digit (i.e. down to 100m) reference is given. To convert that to a normal Irish 6-digit grid reference, just drop two digits from each group, making it O 206 349.

This I gather ties in with the OSI grid reference system as shown in the Dublin City 1:15,000 map.

Nope, see above.

My question is: will the http://www.oziexplorer.com/ map for Ireland show this grid system for the whole country, 26 counties at least.

Yes.

Most OSI maps are at 1: 50,000, i need the 1:15,000 detail

If so what map am I after?
I gather that I need to get the OZI software and then either buy a digital map or scan from paper.

You can't buy digital maps in OziExplorer format. You'll either have to scan them in yourself, or somehow come by a digital raster version of them (in any common graphics format) and calibrate them yourself. The only correlation between the 1:15k Dublin street atlas and the 1:50k OSi maps is that the blue grid lines correspond. The letters and numbers along the side of the pages in the atlas have nothing to do with anything in particular. So to be able to calibrate individually scanned pages from the atlas you'd first have to reference the intersection of the grid lines (which is what you usually use as calibration points) to the equivalent portion of the 1:50k map.

Can I link the etrex to a laptop and be able to show my position on the laptop using the OSI grid reference system?

Yes. You may have to change the output format on the eTrex from Garmin proprietary to NMEA, but yes it'll work.

I see in the OSI converter that they use ETRF89 as the base for the lat/long portion. the etrex only has WGS84. What is the difference please?

How long have you got ? They're basically geodetic models (approximations) of the shape of the earth. WGS84 is a global one, used by the GPS system, ETRS89 is a European one, optimised for the European continent. There's an excellent document on the UK Ordnance Survey website that explains it all in excruciating detail if you're interested. See http://www.ordnancesurvey.co.uk/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf

Unless you're into accuracies beyond what you'll get in practice using a simple handheld GPS, I don't think the difference will be that huge, but bear in mind that the GPS works internally in WGS84, regardless of what coordinate system it's displaying in, and it's internal conversion algorithms, especially when converting height above sea-level will always be less accurate than the coordinate conversions found on websites such as OSGB and OSi. You can display both Irish Grid and WGS84 Degrees/Minutes/Seconds at the same time if you want on the Trip Computer page of the GPS.

Hope this helps. I've got quite a bit of experience using OziExplorer and calibrating the maps, so fire away!

ircoha

Thanks quys.
Alun: I have it since '03 I believe:) and have never updated the software!

So to summarise: I need the europe version of ozidiscovery and then I need to scan a 1:50 map. Once I have it scanned I need to join it all up and then calbrate or is there an alternative approach.

I just checked, it looks as if I need 4 scan widths across and just over 2 down for a 1:50.

A link on the ozi site under the information section suggests using Paint shop pro to blend them all together.
Is this what you use?
Thanks.

Alun

ircoha wrote: »

Thanks quys.
Alun: I have it since '03 I believe:) and have never updated the software!

So to summarise: I need the europe version of ozidiscovery and then I need to scan a 1:50 map. Once I have it scanned I need to join it all up and then calbrate or is there an alternative approach.

I just checked, it looks as if I need 4 scan widths across and just over 2 down for a 1:50.

A link on the ozi site under the information section suggests using Paint shop pro to blend them all together.
Is this what you use?
Thanks.

You can do it like that, and I have done it that way with some success in the past, but personally I now just scan in the sections as is, calibrate them individually, and then use the Ozi MapMerge utility (see Ozi website under Optional Extras) to merge them into one map. One snag with stitching together the images beforehand is that you need to get them absolutely straight. You can do this in some later versions of PaintShop Pro with the 'straighten' tool, but it's not there in some of the older versions. Using MapMerge makes that redundant.

ircoha

Thanks Alun.

Saw the merge stuff later last night, does it cater for overlaps or do the pieces need to be clean?

Have just scanned a section of OSI Discovery No 38 using the windows scanning software with a BenQ scanner
Did it at 125dpi , saved it as a tif file
the file size is 4Mb for an A4 page. Is that about right?

Any merit in increasing the dpi or saving it in another formats?
Any other thoughts?
Thanks

Alun

Overlaps are fine, in fact, you'd want to have at least some overlap to avoid getting any white gaps between scans. The only thing to watch out for is that some scanning software can 'auto expose' which can mean some scanned sections are lighter or darker than others, causing a bit of a visible 'join line'. If possible it's best to scan everything in ona manual setting to get them all the same brightness.

The MapMerge utility creates maps in Ozi's proprietary .ozfx3 format, and after that you don't need the original scanned images, so there's no real point in skimping on resolution. The MapMerge utility is essentally resampling the input images, so if you scan them in at too low a resolution, it'll sdversely affect the quality of the resultant map. I'd do them at 200dpi or more personally, and a non-lossy format such as TIFF is just fine. Like I said, you don't need the images after you've merged them, so no point in skimping on quality. There's a setting in the MapMerge utility that ultimately determines both the size, and the quality when zoomed in, of the resultant .ozfx3 file and I usually use a setting for that of 4 meters per pixel.

Oh yes, and to read the created .ozfx3 files you'll need to download and install the latest version of OziExplorer from the website.

Good Luck!

ircoha

Perfect, will get on with it and revert back when I have some progress made and have more questions.

ircoha

I have a etrex vista which came with 2 separate cables, one for power from cig lighter and the other for data to computer, so cannot use both in the car when connecting it to the laptop.

Just wondering is there a similar GPS unit that comes with a combined cable, or can a combined cable be got for the vista: there seems to be some question as to whether a USB port can provide enough power to the GPS unit.
Thanks

Alun

Which Vista have you got, exactly? Is it one of the newer one with a mini-USB connector, or an older serial port one with that irritating 4-pin slide-in connector?

The mini-USB ones (well mine, anyway) run quite happily with just the USB cable connected, with or without batteries in them.

For the older, serial port versions, you can get a Garmin supplied cable that does power and data in one (see https://buy.garmin.com/shop/shop.do?pID=745). If your laptop has no serial port, you'll also have to get some kind of USB-serial converter.

ircoha

Alun wrote: »

Which Vista have you got, exactly? Is it one of the newer one with a mini-USB connector, or an older serial port one with that irritating 4-pin slide-in connector?

The mini-USB ones (well mine, anyway) run quite happily with just the USB cable connected, with or without batteries in them.

For the older, serial port versions, you can get a Garmin supplied cable that does power and data in one (see https://buy.garmin.com/shop/shop.do?pID=745). If your laptop has no serial port, you'll also have to get some kind of USB-serial converter.

Alun

The older, irritating 4 pin slide in one!!

I have ordered the USB to serial connector.

Will explore the all-in-one cable as well as the newer vista.

Thanks again.

Alun

ircoha wrote: »

The older, irritating 4 pin slide in one!!

I have ordered the USB to serial connector.

Will explore the all-in-one cable as well as the newer vista.

I just had a thought ... you can also get a straight USB to Garmin data cable that will also power the unit. Garmin don't do them AFAIK, but you can get one here http://www.gpsw.co.uk/details/prod2160.html. That way you don't need to plug the GPS into the cig lighter and you can avoid the extra USB-serial adapter as well.

I have just got a Vista HCx and it's a great little thing. I even get a 6 satellite fix with it sitting on my desk near the window!!