Calibrating scanned maps?

[lazerin]

I'm trying to calibrate a VTC for oziexplorer. I'm stuck at the point where I need to know the projection data. I've set it to Transverse Mercator as detailed on the VTC, but now I need the central meridian and lattitude origin. How do I find this out? Where is it written on the VTC?

 

 

[slartibartfast]

I think you need to be using latitude and longitude, not UTM.

 

To calibrate, you just pick at least 3 points (the Maptrax maps have 9 preset for you) and enter their lat and long.

 

Using OziExplorer on your PC, choose "load and calibrate map image", and click on the junction of a latitude and longitude intersection on the VTC. Read the latitude for that point from the VTC (left or right margin) and enter the degrees, minutes and seconds in the box. Then do the same for the longitude (top or bottom margin). Repeat for as many points as you want. It shuold be at least 4 toward each corner of the map.

 

Ignore the UTM Coordinates.

 

I have done this process for a few maps, but I prefer buying them from Maptrax pre-calibrated.

 

Cheers,

 

Ross

 

 

[lazerin]

Thanks Ross, I must be making a mistake somewhere. I tried doing it as you said above, but when I turned on the grid lines to double check the calibration, it was way off. Hence I started playing with the Mercator thingy. Blast, this is too hard, maptrax it is!

 

 

[JayKay]

Hi Lazerin,

 

Don't give up. I also had trouble calibrating the maps with OziExplorer instructions, so I had a look at how others do it and now I calibrate my own maps and I get it spot on.

 

Here's what I do. Using OziExplorer:

 

1. Load Scanned Map File

 

2. Set Map Projection: Polyconic (American)

 

3. Projection Setup: Central Meridian: eg. 147 15.0 E (Enter the Middle Longitude of the Map you've scanned)

 

4. Define 9 points distributed roughly in an "X: shape across map. (One in each corner, one near the centre and four more somewhere between the centre and each corner. That gives you 9 calibration points. For accuracy I use the closest marked map insersections of Latitude and Longitude lines)

 

And that's it. Save the map and enjoy.

 

Because I use these maps in moving map mode I also:

 

5. Set Options: * Include in Moving Map

 

6. Set Corner Markers to corner of map