Map reference grid question
Submitted: Wednesday, Sep 14, 2005 at 01:37
ThreadID:
26440
Views:
3248
Replies:
5
FollowUps:
5
This Thread has been Archived
V8troopie
OK, I bought a 1:100 000 topographical survey map. I scanned a section of this and plan to import it in to ozi explorer.
To calibrate this section I would need the exact lat/long of selected calibration points.
I have no trouble dealing with lat/long coordinates but this map shows only a few of these on the margin and at the wrong area. There are lots of black
grid lines, at 1000m interval, and numbers against them at the margin to establish a
grid reference.
The map has this reference in the SW corner: 6494000mN, 547000mE
So, I obtained a sample
grid reference point : 2431-660160
How do I convert this figure into lat/long?
I did look up google and there are calculators for the northern hemisphere as
well as lots of confusing math formulae - totally mind boggling.
Anybody know of a simple way to do this or of a userfriendly web calculator for Australian locations?
Klaus
Reply By: Coyote - Wednesday, Sep 14, 2005 at 09:17
Wednesday, Sep 14, 2005 at 09:17
It sounds like your map as another
Grid Reference system on it. There are many types of
Grid system used throughout the world. The Lat/Long is just one. In the military we use MGRS (Military
Grid referencing System) at the bottom of the Map should be the type of
Grid Ref used, could be WGS, MGRS etc.. Ozi explorer is pretty flexible with these too. So all you have to do is tell OziExplorer in the settings what
Grid reference system the map you are installing is and then type in the coordinates of three known points, ie a road/crrek
intersection etc.. Ozi exporer will then do the rest for you. (assuming that the map is not an obscure
Grid system that is not recognised by Ozi explorer.
AnswerID:
130010
Follow Up By: The Explorer - Wednesday, Sep 14, 2005 at 09:57
Wednesday, Sep 14, 2005 at 09:57
The map in question is undoubtably showing UTM or TM projection
grid lines in addition to Lat Log and as Davoe has pointed out the numbers are only shown in full in one corner - you have to add the relevant begining and end numbers to get the full number for any one
grid line and enter these into OziExplorer. Military
Grid Referencing systems also shorten the full UTM coordinates - and as with the shortened numbers along edge of map you will need to take them back to the full number before entering them into OziExplorer - there is no option for entering shortened MGRS numbers into OziExplorer (ie it is not "real"
grid system on its own ..it uses shortened UTM/TM coordinates). Also WGS (I assume you mean WGS84) is a datum not a
grid reference. You must of course specify the correct datum when calibrating any map for OziExplorer(that requires any sort of accuracy). On the 100K maps the datum and projection used are generally shown near the scale bar at bottom of map. If it says TM (Transverse Mercator) for projection, use UTM (Universal TM) as it will work fine and removes the need for some addition input of information.
Cheers
Greg
| I sent one final shout after him to stick to the track, to which he replied “All right,” That was the last ever seen of Gibson - E Giles 23 April 1874 Lifetime Member My Profile My Blog Send Message Moderator |
FollowupID:
384480
Follow Up By: V8troopie - Wednesday, Sep 14, 2005 at 15:23
Wednesday, Sep 14, 2005 at 15:23
Thanks Greg and to all the othere who replied.
Its a brand new map from the chart
shop in
Fremantle, not a terrorist map :-0
It does say transverse Mercartor, so I guess I follow the advise of using UTM calibration.
Its just that I never done UTM, always used lat/long for calibration as most of my chart work is on marine charts which do not have the metric
grid reference lines.
I was thinking a bit like some of you older blokes who always convert metric measurements to the old imperial stuff just because it sounds more familiar :-)
I guess I'll just have to get my head around that Northing and Easting way of map reference and let ozi explorer do the number crunching.
Which brings me to another question, will the downloaded track from my GPS still be accurate? The place in question is
Lake Dumbleyung and the track is the one my boat would have done.
Klaus
FollowupID:
384535
Follow Up By: The Explorer - Wednesday, Sep 14, 2005 at 15:36
Wednesday, Sep 14, 2005 at 15:36
Klaus
Once the Map is calibrated correctlly (using lat/long or UTM - dont mattter) and assuming GPS configuration in OziExplorer is right for your particular gps it will plot exactly on spot - OziExplorer does the hard work. I generally use Lat/Long as
well - easier (less numbers to stuff up), especially if you have complete scan of map - each corner of map has the lat/long shown.
Now if you had purchased that wonderful South West WA 50K Raster CD (from C&M
Shop or exploroz) you would not have had any probelms at all (as all maps calibrated and ready to go with OziExplorer)..plus its at 50,000 scale so better detail.
Cheers
Greg
| I sent one final shout after him to stick to the track, to which he replied “All right,” That was the last ever seen of Gibson - E Giles 23 April 1874 Lifetime Member My Profile My Blog Send Message Moderator |
FollowupID:
384537
Reply By: Coyote - Wednesday, Sep 14, 2005 at 09:18
Wednesday, Sep 14, 2005 at 09:18
It sounds like your map uses another
Grid Reference system on it. There are many types of
Grid system used throughout the world. The Lat/Long is just one. In the military we use MGRS (Military
Grid referencing System) at the bottom of the Map should be the type of
Grid Ref used, could be WGS, MGRS etc.. Ozi explorer is pretty flexible with these too. So all you have to do is tell OziExplorer in the settings what
Grid reference system the map you are installing is and then type in the coordinates of three known points, ie a road/crrek
intersection etc.. Ozi exporer will then do the rest for you. (assuming that the map is not an obscure
Grid system that is not recognised by Ozi explorer.
I don't have Ozi exploere here at work with me or I would try and give you clearer directions sorry. e-mail me at damian.reitsma@defence.gov.au if you want more advice.
AnswerID:
130011
Reply By: Bega Photographer - Wednesday, Sep 14, 2005 at 11:29
Wednesday, Sep 14, 2005 at 11:29
G'day Troopie.
You've been given some good and reliable advice already about calibrating your scanned map. Follow it.
Here it is in a nutshell:
Unless you brought the map from some international terrorist it will be in WGS84 datum with UTM map
grid.
Ignor the Lat/Long coordinates. Use the UTM map
grid. It's in 10 km squares. (this line is the answere to your question)
To make it a bit easier, before you scan the map, pencil in the coordinates you will use for calibration along the
grid lines, in the part of the map you'll scan. Give yourself a few alternative lines.
If you are using the free version of OziExplorer you can only use three coordinates for calibrating the map. You need to choose coordinates that are the nearest to the margines of your scanned map.
Try for bottom left, bottom right and top right corners of the map. If the
intersection of
grid lines doesn't cooinside near the borders, then try another combination of map
grid intersections.
Regards,
Laurie.
Visit Laurie's Photos
AnswerID:
130039
Follow Up By: Member - Davoe (Widgiemooltha) - Wednesday, Sep 14, 2005 at 21:17
Wednesday, Sep 14, 2005 at 21:17
No because it is a 100 thou map it probably uses AGD 1966 The 100 thou map in front of me was done in the early 80s and is accurate from 1975 - the 250 thou maps make a better propasition at least in my area
FollowupID:
384592