Hema and Oziexplorer

Submitted: Friday, Jan 21, 2005 at 16:50

ThreadID: 19657 Views:5037 Replies:6 FollowUps:13

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Utemad

I have checked the archives and even rung Hema but to no avail as yet.

I am curious to find out how people find out what datum and projection Hema uses for its maps. They do not put either of these important bits of info on their paper maps. I have emailed them before and they have told me but haven't got back to me this time. They did tell me though that this info is not available on their website either.

I don't understand why such a prominent map making company does not include this info on the map itself. Lots of other map makes include it.

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Reply By: sav - Friday, Jan 21, 2005 at 18:11

Reply By: Kings - Friday, Jan 21, 2005 at 19:15

Reply By: The Explorer - Saturday, Jan 22, 2005 at 00:56

Saturday, Jan 22, 2005 at 00:56

Hello - which Hema maps/areas are you talking about - there are many. They may use different projections for different maps. Also the data required to define a projection changes as you move from area to area..i.e. more info required!
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

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AnswerID: 94365

Follow Up By: Utemad - Saturday, Jan 22, 2005 at 09:58

Saturday, Jan 22, 2005 at 09:58

Hi,

I realise that the info changes map to map which is why I think it should be printed on every map. However the map I am currently wanting info for is the 'Hema Tasmania Handy Map'. I scanned it before I went but didn't have time to stuff around getting this info. Therefore I just made it WGS84 and lat/long. Close but not that close.

Thanks.

FollowupID: 353354

Follow Up By: Pluto - Sunday, Jan 23, 2005 at 09:43

Sunday, Jan 23, 2005 at 09:43

I think you'll find that most Hema maps pulished prior to the GDT series have no references to datum and other calibration info. It wasn't untill GDT that they realised the value of including this info (lets face it, when you are using a paper maps as an ordinary road map, without relating it to a GPS, what use does the datum have? the only thing that matters in this case, is the noted distance between intersections).

I have scanned and calibrated a number of older hema maps without too much trouble, with the one obvious exeption. The original release of the Central Australia map was beyond me. I just couldn't get the map grid and the Ozi grid overlay to line up. I emailed Hema, who were as helpful as they could be. In the end the map was originally created by "rubber sheeting" a number of other maps with different projections. So the map was never intended to be to scale.

I don't believe they have practiced this method of map construction since GDT was released.

FollowupID: 353448

Follow Up By: The Explorer - Sunday, Jan 23, 2005 at 12:11

Sunday, Jan 23, 2005 at 12:11

Ok - as pointed out by others it may not be possible to calibrate the map to the level of accuracy you would expect. Have you tried using lat/long along with the "Use Polynomial Calibration for map" (found within OPTIONS on the menu availble when calibrating a map)

If this option is ticked OziExplorer will use 2nd order polynomial calculations when calibrating the map. This allows maps to be calibrated even if they are not truly square (linear). This is useful for calibrating maps where the true map projection is not known.

To use this option you must have 7 or more calibration points specified. If you can get enough points from the map directly use waypoints of known points (your own or use namesearch database).

Limitations - Using a polynomial calibration on a truly linear map can cause unpredictable results.

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

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FollowupID: 353464

Follow Up By: Pluto - Sunday, Jan 23, 2005 at 12:51

Sunday, Jan 23, 2005 at 12:51

I can't say that it had occured to me. Thanks for the idea.

That only problem I can see with it is, this map will need more than 9 Calibration points. I believe Ozi can use up to 30 calibration points, but the thought of calibrating it with a text editor is a bit daunting.

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Follow Up By: The Explorer - Sunday, Jan 23, 2005 at 13:49

Sunday, Jan 23, 2005 at 13:49

Pluto - If the map has variable scale across it (like maybe a rubber sheeted map would??) even the polynomial method may not work if applied to the entire map....can say I have used it much in the recent past. Maybe I missed soemthing but why more that 9 calibration points? For polynomial the more the merrier I imagine but 7 is the minimum requirement
Another thought...
If you do need to use more than 9 (because maybe the map is large or is really screwed up) maybe you could just calibrate separate areas as seperate map files and get away with using less calibration points (for each individual section..if you know what I mean).
Arrhh calibrating your own maps - what great fun!! Im slowly doing my 50K Kimberley series..only ~300 to go!!
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

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FollowupID: 353472

Follow Up By: Pluto - Sunday, Jan 23, 2005 at 15:14

Sunday, Jan 23, 2005 at 15:14

He He... Good luck!

Have a look at the Ozi help file. The section where it discusses file formats. I'm fairly sure it has a limit of 30 cal points per map (I can't check at the moment). Of course the internal calibration facility only allows you to access the first 9. In only extreme cases is 9 insufficient.

Your idea of calibrating sections of the map could also be taken one step further by, copying the calibration points from the different section calibrations and pasting them into a single map calibration file. Definitely worth experimenting.

FollowupID: 353480

Follow Up By: Utemad - Sunday, Jan 23, 2005 at 20:53

Sunday, Jan 23, 2005 at 20:53

Hi Explorer,

I tried using the polynomial and lat/long like you suggested. Just by looking at the track files on the map now I'd have to say it was pretty close to being right.

Thanks for the info.