Mapsource readable ford database

Mouse

Mouse

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Doh!

I can see the error, it may occur in other files but typically it didn't occur in any of the files I actually tested.

I'll put up a fixed version later today.

I think the only files affected are East Sussex and West Sussex. It's to do with the locations of the waypoints being near zero longitude.
 
I have checked a number of point by zooming in.

Looks a bit strange as a lot of them are not on a road nor a river :confused:
 
The new corrected data is now online at the same address.

The comment about the waypoints not lying exactly on the roads is correct. There are two problems here.

Firstly, the original data is not 100% exact. The locations listed on the web site are accurate to about 50 metres. If you search for a specific location using, for example, multimap.com or streetmap.co.uk, the location will not be exactly on the ford in question.

Secondly, the conversion of OS coordinates to latitude and logitude is not an exact process either. It's also possible that my conversion routines use a different base datum for the lat/long coorindate system than do MapSource and various mapping websites. This can introduce an error of up to about 5 arc seconds in the converted data.

But I think most of the waypoints are close enough to allow you to find the right bit of road.

If I find a better way of doing the conversion, I'll update my files.
 
Mouse said:
The new corrected data is now online at the same address.

The comment about the waypoints not lying exactly on the roads is correct. There are two problems here.

Firstly, the original data is not 100% exact. The locations listed on the web site are accurate to about 50 metres. If you search for a specific location using, for example, multimap.com or streetmap.co.uk, the location will not be exactly on the ford in question.

Secondly, the conversion of OS coordinates to latitude and logitude is not an exact process either. It's also possible that my conversion routines use a different base datum for the lat/long coorindate system than do MapSource and various mapping websites. This can introduce an error of up to about 5 arc seconds in the converted data.

But I think most of the waypoints are close enough to allow you to find the right bit of road.

If I find a better way of doing the conversion, I'll update my files.
Click to expand...

Apologies if this is teaching Granny to suck eggs, but have you got them on the same datums? Most really modern maps are on WGS84 or the Euro equivalent, but Ord Survey more than a year or 2 old are on OSGB36 - the difference being anything up to 150metres or so. And the GPS unless reset is likely to operate to WGS too.

On OSGB, OS refernces should convert accurately to lat / long
 
birdseye said:
Apologies if this is teaching Granny to suck eggs, but have you got them on the same datums? Most really modern maps are on WGS84 or the Euro equivalent, but Ord Survey more than a year or 2 old are on OSGB36 - the difference being anything up to 150metres or so. And the GPS unless reset is likely to operate to WGS too.
Click to expand...

The algorithm I used for the conversion uses the OSGB36 datum. MapSource has a menu allowing you to choose the coordinate system and datum in use, but I suspect this may only be for display purposes. I think, when importing data, it will probably just use WGS84.

So - if I understand the situation correctly, I need to find details on WGS84 and update my conversion routines.
 
Are you sure that MapSource 5 won't load .gpx files? If not, let me know what file types are in its menu, and I'll see what I can do.

I can't test this as I have MapSource 6.5. Upgrades are free, by the way, I think.
 
Mouse said:
The algorithm I used for the conversion uses the OSGB36 datum. MapSource has a menu allowing you to choose the coordinate system and datum in use, but I suspect this may only be for display purposes. I think, when importing data, it will probably just use WGS84.

So - if I understand the situation correctly, I need to find details on WGS84 and update my conversion routines.
Click to expand...

Sorry, but I'm not sure how old were the maps the locations were derived from the first place so I can comment answer for sure.

OS have been redrawing the UK maps using satellite mapping and this has made them much more accurate. At the same time I would expect they have changed over to WGS84 datum (or the Euro equivalent) just like UKHO has done for marine charts. If you then take the lat / long of somwhere off the old maps and on the old OSGB datum, and use it on a new map on the WGS84 datum , there will be a discrepancy. On the marine charts with which I am much more familiar, the position shift is in the 100metre range most of the time.

My marine GPS can operate to many datums, but it does not have mapping. I dont know what Garimin do with kit like the Quest. I suspect that the GPS will be pre-set to use the same datum as the maps built into the machine and my guess is that would be WGS. In which case, to cut a long and boring monologue short, you most likely need to do exactly what you said in the first place and modify your algorithm to adopt WGS.
 
No it's not free, mapsource is £90 to uprgrade otherwise I would!
Files supported are: *.wpt way points *.rte Routes *.trk Tracks
Regards
 
birdseye said:
My marine GPS can operate to many datums, but it does not have mapping. I dont know what Garimin do with kit like the Quest. I suspect that the GPS will be pre-set to use the same datum as the maps built into the machine and my guess is that would be WGS. In which case, to cut a long and boring monologue short, you most likely need to do exactly what you said in the first place and modify your algorithm to adopt WGS.
Click to expand...

I think you are right - I added code to my program to compensate for the difference between the OSGB36 datum and WGS84, and this has certainly improved the accuracy of the waypoint data. Most of the waypoints are still not "bang on", but the positions seem to be accurate to within about 50m in most cases.

So I think, this is "good enough" :)
 
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