Yeah. Just checked and my 2011 version is just as inaccurate. Perhaps that's why I ended up going down the wrong valley from Scafell Pike in the mist. Hope we can get this sorted.
Bri

Hi,

Yes it's an issue that I have with all my 25k "Selections" maps supplied over a period of several years (some quite recently) but the magnitude depends on the region of the UK. It's not a major problem for separate areas over the country, which can be calibrated individually by changing the "Map Properties" on the PC. However, I'm surprised more aren't complaining about the DMS maps which can contain activated regions from the whole UK but only have a single calibration offset available (and of course may be download directly to mobile device software which AFAIK doesn't permit "local" calibration).

For my maps, I've needed to use shifts of about +0N, +8E metres for the London area but +10N, +18E metres for Stirling (Scotland).

Cheers, Alan.

Alan,

Thank you for your input. You seem well versed in things Memory Mappy!

I shall check my maps more carefully from now on and enter datum shifts as appropriate. It's becoming apparent that it's not a software bug or similar, just inaccuracies in the maps themselves.

Like you I'm surprised more aren't complaining. Many of my GPS recorded tracklogs, imported into Memory Map, are clearly slightly shifted from where they should be. The errors become most obvious when the tracklog follows a well defined feature like a river or road.

Cheers

Geoff

Hi

I wonder if this is to do with the distortions caused by inaccuracies in the original trig surveying?

Up to about 10 years ago the OS had spreadsheets (etc.) for doing coordinate conversions but as GPS became more mainline for surveying the OS started publishing various transformation utilities on their website, I think mostly because also at this time (the time, or shortly after, they went digital?) they "tweaked" the maps to remove the (known to them) distortions rendering the older calculations obsolete. I recall the distortions vary across the country depending on the accuracy of the original surveying and I think are "worst" in the mountainous areas.

Up till then the coordinate calculations were "linear" and may examples can still be found on the web or embedded in progams with source available. I think these legacy (as the OS seems to call them) approaches can also still be tracked down in an old corner of the OS web site for those who need to "undo" old calculations before "redong" them with the new ones.

I wonder if MM is still coded with the legacy approach rather than the new alternatives recommended (and detailed) on the OS web site here:
http://www.ordnancesurvey.co.uk/oswebsi ... loper.html

And much interesting info on this (and other GPS & Positioning topics) here:
http://www.ordnancesurvey.co.uk/oswebsi ... index.html

(edit/update) Having read a bit more about OSTN02, the 2002 Transformation, it doesn't look like the differences introduced / corrected by that are anything like 19m & 7m being discussed in an earlier post

I didn't get a response from "support" when I emailed them. It's obviously gone in the too difficult box, along with "having a workable system for buying maps".

I have not seen an email regarding this, is there any chance you could resend it to support@memory-map.co.uk - Thanks Jason

It's a shame is it not. I still find it very annoying. I have had to move mine quite a bit in this area. But I am not sure what I will find in other area's. And of course you can't move it on your mobile device.

Bri

Just a slight update on this. I have a walk around Twice Brewed lined up. Part of it is walking down a small road. When I brought the 2012 version up on my Android, I was walking down a field. I then changed it to the older version and I was walking down the road OK with that!

Bri

Jason,

Did you check the OS master files?

Did you find the errors described here?

Geoff

geoffmoss,

We checked some areas on the OS master files, but could not find errors as large as suggested by the posts here.

Thanks

Jason,

How big were the errors you found on the master files?
What did you compare the master files with to discover those errors?

If the master file errors are significantly different to those found on the Memory Maps used in the software, then maybe an error is creeping in during the conversion of the master files to the qct files we users buy.

I've created a Memory Map route you can use to easily check the map calibration of the Lake District National Park. I've emailed it to you using the support@memory-map.co.uk address.

The route zig zags over every part of the park and every waypoint has a nice round grid reference that should place it exactly on a grid line intersection. Overlaying it on the OS 1:25k Lake District map, none of the waypoints line up with grid line intersections. The map calibration error is worst in a West to East direction. On the west side of the park the waypoints appear about 18m west of where they should be. On the east side of the park they are about 14m west of where they should be.

A datum shift of 5m N and 16m E will line up the map much better with the waypoints.

As a fan of Memory Map I'm keen to discover where the errors come from and hopefully help eradicate them.

Cheers

Geoff Moss