EOTopo question??

Submitted: Thursday, Oct 27, 2016 at 11:55
ThreadID: 133672 Views:2388 Replies:3 FollowUps:6
This Thread has been Archived
Using EOTopo 200k maps.
Whe driving adjacent to a railway line, say within about 200m of the line- the pointer tends to follow the railway line ??
It's not a big issue but just wondering??
Cheers
Wombat100
Back Expand Un-Read 0 Moderator

Reply By: Member BarryG - Thursday, Oct 27, 2016 at 15:22

Thursday, Oct 27, 2016 at 15:22
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
AnswerID: 605457

Follow Up By: The Explorer - Thursday, Oct 27, 2016 at 16:15

Thursday, Oct 27, 2016 at 16:15
Hi - a calibration problem is not the issue - read my reply below.

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  My Position  Send Message
Moderator

0
FollowupID: 875219

Reply By: The Explorer - Thursday, Oct 27, 2016 at 16:13

Thursday, Oct 27, 2016 at 16:13
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
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  My Position  Send Message
Moderator

AnswerID: 605460

Reply By: Member - Stephen L (Clare SA) - Thursday, Oct 27, 2016 at 18:29

Thursday, Oct 27, 2016 at 18:29
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
Simpson Desert Colours

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 605461

Follow Up By: The Explorer - Thursday, Oct 27, 2016 at 18:33

Thursday, Oct 27, 2016 at 18:33
"The only map that will give you spot on tracking on OzliExplorer is the new Hema 150 k map."

That is incorrect - there a many maps that plot "spot on" in OziExplorer. e.g. - all maps calibrated correctly, with uptodate data and where plotted data hasn't been purposely offset.

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  My Position  Send Message
Moderator

0
FollowupID: 875223

Follow Up By: Member - Stephen L (Clare SA) - Thursday, Oct 27, 2016 at 18:42

Thursday, Oct 27, 2016 at 18:42
Hi Greg

Totally agree, but when you run EOTopo and the Hema side by side, it shows just how much more accurate the Hema is.

When in an area that has more accurate maps available I always use them, but am purely stating facts between the two maps.



Cheers



Stephen
Simpson Desert Colours

Lifetime Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 875224

Follow Up By: The Explorer - Thursday, Oct 27, 2016 at 18:53

Thursday, Oct 27, 2016 at 18:53
No worries - your comment was somewhat ambiguous and suggested to me (at least) that you thought there were no other maps besides Hema 150 that plotted correctly in OziExplorer....anyway ...

Generally speaking, larger scale maps will be more accurate at depicting features than smaller scale maps...even if they used the same base data.

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  My Position  Send Message
Moderator

0
FollowupID: 875225

Follow Up By: Member - Stephen L (Clare SA) - Thursday, Oct 27, 2016 at 19:15

Thursday, Oct 27, 2016 at 19:15
Hi Greg

I should have included these before, but as you can see, there is too much variation to make it accurate.








Cheers


Stephen
Simpson Desert Colours

Lifetime Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 875227

Follow Up By: The Explorer - Thursday, Oct 27, 2016 at 19:27

Thursday, Oct 27, 2016 at 19:27
Again - no worries...though I never passed comment on how up to date EoTopo was compared to any other map...I was addressing the OP's issue which relates to the offsetting of roads, rail lines (and other features) so that they can be plotted on a 200/250 scale map. In this case that was the issue - not out of date track plotting.

All maps (even Hema's) will become "inaccurate" over time if not updated.

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  My Position  Send Message
Moderator

0
FollowupID: 875228

Sponsored Links

Popular Products (13)