EOTopo question??

Hi Wombat,

EOTopo are raster maps, so the pointer shouldn't "jump" onto a road or rail line (as vector-based street mapping might do).
I assume that you are using OziExplorer or Memory Map. Each of these products knows your position from the GPS satellites and they have a set of maps whose corner positions are known. The program then displays the appropriate map and shows your position on that map. If you are seeing your pointer travelling down the rail line while you are driving on the road (200m away), then perhaps the map file has an error. Where exactly did you experience this problem?

Regards
Barry

Hello

Because of the original small scale of these type of maps (200/250K) it is not possible in some circumstances to show roads and railway lines (or other features) that are directly next to each other, in their exact position.

Why? Because, for example, the road is depicted on the map by a line that is much wider than the road itself -

e.g, a major road may be shown as a 200m wide red line when in reality it is only 20 m wide. If it were plotted in the correct position and 200m wide it would over write the line showing the position of the railway line which is less that 100m away.

The solution to this problem is to offset some roads (or railway lines) so that both can be shown on the map. When these maps are used on GPS units obviously your position shown on the GPS screen will therefore not necessarily correspond with the road you are on.

If you want better accuracy you would have to use a larger scale map (e.g. 100k, 50k or 25k)

Hope this makes sense.

Cheers
Greg

Hi Wombat

It is not just railway lines for the EOTopo 200 maps.

I have contacted David about this issue a number of times and it comes down to them using the old Natmaps as a starting point.

The only map that will give you spot on tracking on OzliExplorer is the new Hema 150 k map. I prefer the colour and features of the EOTopo, but needs a full revamp to make many of the tracks more accurate.

A very good example of this is driving the Birdsville Track, which has not had any major realignment in many years. A good number of sections of the EO Topo has you driving off raid, by many kilometres, while the Hema 150 is spot on. These are not the only sections, there are countless other examples I could state.

So it is not you or you mapping system, unfortunately it is the map and do not let anyone else tell you any different.

If you want proof, I could show many examples as screen shots.



Cheers




Stephen