Creating routes with Memory Map

[jonners]

I am just in the process of trying out 1:50,000 Memory Map software to create routes on the PC and send to my unit. I run a 60CSx with Topo GB installed.

 

Having created a Memory Map route on mountain paths in the Lake District, and sent it to the GPSr, I find the waypoints that I placed on path intersections with the Memory Map software don't line up with the same intersections on my Topo GB. They are off by about 120'. I have tried setting the map datum to Ordnance Survey Grid and to WGS84, but neither cures the problem.

 

The reason I am concerned is that I would eventually like to get the 1:25,000 version of Memory Map. Before I shell out the extra dosh I want to know if I might have similar accuracy problems.

 

Has anyone out there with Memory Map (1:50,000 or 1:25,000) and Topo GB found discrepancies between the two? I'd be grateful to hear of your experience.

[Nediam]

I have Memory Map and use it on my PDA whilst out walking and caching. I have the 50,000 scale maps and also the 25,000 for the Peak District.

 

I've noticed that most of the time, the route on the ground does not match the route shown on the map (both the 50,000 and 25,000). I don't know why though. It may be that the route on the ground has changed over the years or that the map makers were not that bothered about being too accurate with footpath layouts and chose to just show that there was a right of way in that area.

 

The road layouts though are usually very accurate

[+KlustaDuk]

Me too. I use both MM and Topo GB v2. There always seem to be minor discrepancies between routes plotted visually on mapping software and the actual paths on the ground. Roads are more accurate, but when you factor in their size and the 'lock to road' features of the GPS that's kind of understandable.

 

I've no idea what causes it really, but I always assumed it was a something to do with the curvature of the earth, the flat map projection and the way the maps are then aligned with the underlying survey system. That's why no matter which survey system and which map projection you use they are all out slightly.

 

There must be someone who works in this particular field, on this forum, that knows the real answer.

[jonners]

How much error would you estimate that you are seeing? I'm fairly sure it isn't the paths moving over the years (though I know what you mean), as I have cross-referred the junctions to contour features.

 

To give the best example, there is a multi-path intersection at Esk Hause near to Scafell Pike. It is positioned on a saddle formation in the land that is quite a specific topo feature. On the Memory Map software I have placed my waypoint at the path intersection. But when I upload it to my GPSr it shows the waypoint 120' to the south of the intersection as it is shown on Topo GB.

 

[following added]

 

Having just looked closer at the two programs (Topo GB and Memory Map) I now realise that the paths are shown in different places by each of them. My waypoint appears in the same place on each when related to the contour features, but not when related to the paths.

Edited April 19, 2007 by jonners

[Nediam]

How much error would you estimate that you are seeing?

Sometimes it is only a few feet however, recently is was around 200 feet out in one area! I'd say on average about 50 or 60 feet.

[+keehotee]

but when you factor in their size and the 'lock to road' features of the GPS that's kind of understandable.

I thought it was only navigation software such as TomTom that used "lock to road"...?

AFAIK MM just overlays a cursor based on your current position - as read from the GPS - onto a map, without using any software to alter that position depending on where it thinks you are.....

[+CrazyL200]

I thought it was only navigation software such as TomTom that used "lock to road"...?

AFAIK MM just overlays a cursor based on your current position - as read from the GPS - onto a map, without using any software to alter that position depending on where it thinks you are.....

 

Correct, MM has no navigational functions other than the directional "Goto Mark" function.

It has no idea where you are in terms of roads, paths etc...

 

Who knows, one day, it'll be possible to buy a navigation system, at a reasonable price, that uses MM.

In the mean time, if you use something like Tomtom and MM on the same PDA with GPSgate, you can have MM on screen, with TT running in the background, giving verbal directions.

Edited April 20, 2007 by CrazyL200

[+Jonovich]

Who knows, one day, it'll be possible to buy a navigation system, at a reasonable price, that uses MM.

In the mean time, if you use something like Tomtom and MM on the same PDA with GPSgate, you can have MM on screen, with TT running in the background, giving verbal directions.

 

Agreed... as MM is bitmap based, TT is vector, we'll not get routing on MM unless there is some kind of TeleAtlas style vector mapping merged in with it. Closest I have seen in a commercial product is the Road Angel Adventurer 7000. OS maps and a Sat Nav system on the same box, but not strictly routing via OS.

 

J