Lon/Lat Locations

Geoff Lane said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Microsoft's Autoroute will do this, if that's any help.

--

R
o
o
n
e
y

Rooney said:

Geoff Lane said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Microsoft's Autoroute will do this, if that's any help.

Forgot about that one - thanks.

Geoff Lane

In article <[email hidden]>, Geoff Lane
<[email hidden]> writes

Quoted message said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Multimap allows you to search for postcodes and display them on a map.
You can also click on the map to recentre it and then read off the
co-ordinates below the map.

http://www.multimap.com/map/browse.cgi?lat=51.3355&lon=0.0012&scale=10000
&icon=x

Quoted message said:

Reason I ask is that I have a Garmin Etrex and I have often used it to
get to a location by entering the postcode on Streemap.com which then
gives me numerous map references - last week I used it to go to a
location near Croydon and when I neared my destination it was advising
a left turn where in fact I needed to turn right.

The Garmin's data showed it to be about a mile wrong so I'm thinking,
either;

1. The Garmin is wrong (Doubtful)

I expect that the Garmin datum may not be set to the same as that used
by the co-ordinates source (Streetmap in this case). Streetmap's
co-ordinates will either be in OSGB36 or WGS-84. The Garmin datum is set
under the Setup, Units, Map Datum field. Garmin call OSGB36 Ord Svy GB.

Quoted message said:

2. Streetmap.com's data may be incorrect (possible but not sure).

On reaching the location I took an actual reading from the Garmin and
they are as follows;

Incorrect N51:20:10, E0:0:16
Actual N21:21:00, E0:0:33

The other thing to check is that the format is the same. In the example
above it looks like you are working in degrees, minutes and seconds. Are
you sure that

(a) streetmap is giving you the co-ordinates in that and not
degrees and decimal minutes for instance

and

(b) the Garmin's Position Format is set to hddd mm ss.s

--

Dominic Sexton

Geoff,

I can think of 2 potential problems :-

1. The lat, lon returned from Streetmap is probably the postcode
'centroid' - this is the point at the centre of the postcode polygon.
Most postcodes cover a range of addresses and so are a polygon
containing an area. This is approximated to a centroid on Streetmap in
order to simplify it. You were probably directed by the eTrex to the
centroid rather than a speicifc address. The actual centroid is probably
in the middle of someone's back garden.

2. You may have the datum set incorrectly. Streetmap will give you lat
and lon in the OSGB1936 datum whereas your etrex will natively use the
WGS84 datum unless you have set it otherwise. The difference between the
two is about 400m.

Regards

Andrew

--
Andrew Whaley, author of :-

Trailgauge - Shareware 3D GPS Mapping Software
Free Download from http://www.trailgauge.com

"Andrew Whaley" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

2. You may have the datum set incorrectly. Streetmap will give you lat and
lon in the OSGB1936 datum whereas your etrex will natively use the WGS84
datum unless you have set it otherwise. The difference between the two is
about 400m.

Andrew are you sure that this is the datum streetmap give because if you use
this page it specifies that lat long is in WGS84 in the results
http://www.streetmap.co.uk/gridconvert.html

Rgds Alan

Geoff Lane said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Reason I ask is that I have a Garmin Etrex and I have often used it to
get to a location by entering the postcode on Streemap.com which then
gives me numerous map references - last week I used it to go to a
location near Croydon and when I neared my destination it was advising
a left turn where in fact I needed to turn right.

The Garmin's data showed it to be about a mile wrong so I'm thinking,
either;

1. The Garmin is wrong (Doubtful)
2. Streetmap.com's data may be incorrect (possible but not sure).

Quite likely. Postcodes can be as precise as one building or as vauge
as the whole of a long street.

What I would do is find the street in streetmap and then go to the OS
1:50k mapping on streetmap (click the arrows between the + and -) and
check or read off the Grid Reference for the address and then enter
that into your GPS as a waypoint. In this case your GPS should be set
to OSGB position format and Ord Srvy map datum.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Bitstring <[email hidden]>, from the
wonderful person Phil Cook <[email hidden]> said

Quoted message said:

Geoff Lane said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Reason I ask is that I have a Garmin Etrex and I have often used it to
get to a location by entering the postcode on Streemap.com which then
gives me numerous map references - last week I used it to go to a
location near Croydon and when I neared my destination it was advising
a left turn where in fact I needed to turn right.

The Garmin's data showed it to be about a mile wrong so I'm thinking,
either;

1. The Garmin is wrong (Doubtful)
2. Streetmap.com's data may be incorrect (possible but not sure).

Quite likely. Postcodes can be as precise as one building or as vauge
as the whole of a long street.

Or, out here, as vague as most of a village - that's about 2-3 square
miles by my calculations. Steetmap gives a one point estimate for the
post code, after that you're on your own. Any day now the PO will decide
to use 12 digit OS references instead. 8>.

--
GSV Three Minds in a Can
Outgoing Msgs are Turing Tested,and indistinguishable from human typing.

Phil Cook said:

On Mon, 10 Jan 2005 18:14:25 +0000, Geoff Lane wrote:

Quoted message said:

Quoted message said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Quoted message said:

Quoted message said:

Reason I ask is that I have a Garmin Etrex and I have often used it to
get to a location by entering the postcode on Streemap.com which then
gives me numerous map references - last week I used it to go to a
location near Croydon and when I neared my destination it was advising
a left turn where in fact I needed to turn right.

The Garmin's data showed it to be about a mile wrong so I'm thinking,
either;

1. The Garmin is wrong (Doubtful)
2. Streetmap.com's data may be incorrect (possible but not sure).

Quoted message said:

Quite likely. Postcodes can be as precise as one building or as vauge
as the whole of a long street.

Quoted message said:

What I would do is find the street in streetmap and then go to the OS
1:50k mapping on streetmap (click the arrows between the + and -) and
check or read off the Grid Reference for the address and then enter
that into your GPS as a waypoint. In this case your GPS should be set
to OSGB position format and Ord Srvy map datum.

But even that can sometimes be wrong, due to errors somewhere. I've
been finding addresses or post codes for some time in Streetmap, then
refining it by clicking on the spot, and using the OSGB map ref as a
waypoint. But a while back in London it reliably gave the wrong ref by
about 400m, which had me going round on foot in circles until I
stopped believing the GPS and going back to map navigation.

I checked it out carefully afterwards, and there's a section of
the map where all refs are displaced by the same amount NE.

The address is Grafton Terrace, London, NW5 4HY, if anyone wants to
check it out. Streetmap gives map ref 527750 185250 for this, but
using that grid ref as input jumps the pointer to Duboyne Rd, about 400m
NE. Clicking on these two different points of the map gives the
*same* grid ref.

I wrote to Streetmap two months ago with those details. They
acknowledged my email immediately "will look into it, you'll hear from
us later", but nothing since. I just checked to see if they've fixed
it -- they haven't.

So I've added an extra routine in my use of Streetmap to check against
this. After clicking on the point to give me the OSGB ref, I simply
then click on "SEARCH" again so that it searches for the grid ref it
already supplied. The pointer shouldn't move. If it jumps the pointer
badly that is the symptom of this particular error.

Apart from that one time, I've found this be a very useful and
reliable way of getting to places. The nominal accuracy is 50m plus
mapping errors. When moving within the grid of city streets that
almost always means you're in the right street and the place is
visible by the time you reach the waypoint.
--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

In message <[email hidden]>, Geoff Lane
<[email hidden]> writes

Quoted message said:

Are there any other sites other than www.streetmap.com that will give
a location if you enter a map co-ordinate?

Reason I ask is that I have a Garmin Etrex and I have often used it to
get to a location by entering the postcode on Streemap.com which then
gives me numerous map references - last week I used it to go to a
location near Croydon and when I neared my destination it was advising
a left turn where in fact I needed to turn right.

The Garmin's data showed it to be about a mile wrong so I'm thinking,
either;

1. The Garmin is wrong (Doubtful)
2. Streetmap.com's data may be incorrect (possible but not sure).

On reaching the location I took an actual reading from the Garmin and
they are as follows;

Incorrect N51:20:10, E0:0:16
Actual N21:21:00, E0:0:33

The incoorrect reference shows on streetmap.com as in Layhams Road but
my Garmin was suggesting West of Henrys Drive into Fairchilds Avenue.

I appreciate there are inaccuracies in GPS but this was telling me a
deffinite left was needed whereas it was actually a right turn.

Any comments or suggestions welcomed.

I have postcode data available, though only to 100m accuracy. It all
comes from the same source originally, though having checked Chris's
example from elsewhere in the thread my figures differ from streetmap in
the last digit, even after maximum allowance for rounding. This makes a
minimum discrepancy of 223m (100m Easting and 200m Northing). My
figures are SE of streetmap, but unfortunately Chris says the deviation
is NE.

If you tell me the postcode you entered I can let you have my figures
for comparison and will also might be able to tell you whether the
postcode has any particular features that might explain the deviation.

--
Michael Farthing
Aardvark Ltd

GSV Three Minds in a Can said:

Any day now the PO will decide
to use 12 digit OS references instead. 8>.

No we wont.
See Andrew Whaley's post.

Anyway, we're Royal Mail ;-P

Chris

Dominic Sexton said:

I expect that the Garmin datum may not be set to the same as that used
by the co-ordinates source (Streetmap in this case). Streetmap's
co-ordinates will either be in OSGB36 or WGS-84. The Garmin datum is set
under the Setup, Units, Map Datum field. Garmin call OSGB36 Ord Svy GB.

Never even looked at that, my Garmin is set to default which I've just
looked at and is WGS-84

Quoted message said:

The other thing to check is that the format is the same. In the example
above it looks like you are working in degrees, minutes and seconds. Are
you sure that

Yes, I sussed the difference and am intentionally using degrees,
minutes and seconds.

Geoff Lane

Andrew Whaley said:

1. The lat, lon returned from Streetmap is probably the postcode
'centroid' - this is the point at the centre of the postcode polygon.
Most postcodes cover a range of addresses and so are a polygon
containing an area. This is approximated to a centroid on Streetmap in
order to simplify it. You were probably directed by the eTrex to the
centroid rather than a speicifc address. The actual centroid is probably
in the middle of someone's back garden.

No, I've rechecked it by entering the long/lat into streetmap.com and
it shows on the map a different location to where it directed me; not
too far out but about half a mile al least.

Geoff Lane

Quoted message said:

I agree with others, your datum in the garmin is still osgb36 when
these mapping programs all seem to use wgs84 and utm.

I've checked my Garmin and it shows WGS84

Geoff Lane

Phil Cook said:

What I would do is find the street in streetmap and then go to the OS
1:50k mapping on streetmap (click the arrows between the + and -) and
check or read off the Grid Reference for the address and then enter
that into your GPS as a waypoint. In this case your GPS should be set
to OSGB position format and Ord Srvy map datum.

I'll give this a try - I am returning to the location next week so
will have another go.

I live in NW London and this location is in the Kent area.

Geoff Lane

Dave Fawthrop said:

On Wed, 12 Jan 2005 18:17:57 +0000, Geoff Lane
<[email hidden]> wrote:

| On Mon, 10 Jan 2005 21:51:04 +0000, [email hidden] wrote:
|
| >I agree with others, your datum in the garmin is still osgb36 when
| >these mapping programs all seem to use wgs84 and utm.
|
| I've checked my Garmin and it shows WGS84

Then reset it to National grid for use in the uk.

However then make sure you feed it positions in OSGB datum. The
easiest way to do that is to feed it positions in Grid Refference form
rather than Lat Long. If you do feed it Lat Long you need to be sure
which Lat Long the position is published in.

On Streetmap Lat Long is given as WGS84 (in two formats D:M:S and
decimal Degrees) so if you were entering that you would hve to set
your GPS to WGS84. However to enter the Grid Reference which streetmap
call LR (Landranger Reference) you will have to have yiour GPS set to
OSGB and add in the zeros to convert the six figure reference to a ten
figure one:

AB 123456 becomes AB 1230045600

Quoted message said:

I had my Garmin set to WGS84 and it was about a kilometer out from National
grid, OS Explorer maps. I changed it to whatever garmin call the
National grid and it is now near enough spot on against the National Grid.

All maps I have ever seen in the UK use the national grid, even though they
quite often do not state it explicitly. There was a thread about pre war
maps on urw recently.

I have an AA road atlas knocking about in which I pencilled in the
National Grid letters and numbers on the 10km grid on the page
margins.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Phil Cook said:

Quoted message said:

| >I agree with others, your datum in the garmin is still osgb36 when
| >these mapping programs all seem to use wgs84 and utm.
|
| I've checked my Garmin and it shows WGS84

Then reset it to National grid for use in the uk.

However then make sure you feed it positions in OSGB datum. The
easiest way to do that is to feed it positions in Grid Refference form
rather than Lat Long. If you do feed it Lat Long you need to be sure
which Lat Long the position is published in.

If I reset my Garmin will the waypoints I already have in the Garmin
still be valid?

This mapping theory is quite complicated but fascinating.

Geoff Lane

Bitstring <[email hidden]>, from the
wonderful person Geoff Lane <[email hidden]> said

Quoted message said:

Phil Cook said:

Quoted message said:

| >I agree with others, your datum in the garmin is still osgb36 when
| >these mapping programs all seem to use wgs84 and utm.
|
| I've checked my Garmin and it shows WGS84

Then reset it to National grid for use in the uk.

However then make sure you feed it positions in OSGB datum. The
easiest way to do that is to feed it positions in Grid Refference form
rather than Lat Long. If you do feed it Lat Long you need to be sure
which Lat Long the position is published in.

If I reset

if you mean 'change the datum/format to WGS84' then yes.. if you mean
'reset', as in 'hard reset', you lose everything, but it's pretty hard
to do that (not even in the manual IIRC)

Quoted message said:

my Garmin will the waypoints I already have in the Garmin
still be valid?

Yes, internally they all store locations as WGS84 .. it's only for
input/output purposes that they are willing to try to translate them
into the 1001 different sorts of garbage in use around the world.

Another wrinkle that I just tripped over and had forgotten about - OS
grid references are always truncated, never rounded. Not a problem if
you use 10 digit references, but if not then SO12399 45699 turns into a
6 figure reference SO123456 .. about 1.4Km out from the first one.

--
GSV Three Minds in a Can
Outgoing Msgs are Turing Tested,and indistinguishable from human typing.

GSV Three Minds in a Can said:

Another wrinkle that I just tripped over and had forgotten about - OS
grid references are always truncated, never rounded. Not a problem if
you use 10 digit references, but if not then SO12399 45699 turns into a
6 figure reference SO123456 .. about 1.4Km out from the first one.

You're an order of magnitude out there! It's only about 140m from
SO123456 to SO1239945699
--
Phil Cook looking north over the park to the "Westminster Gasworks"

In article <[email hidden]>, GSV Three Minds in a Can
<[email hidden]> writes

Quoted message said:

Bitstring <[email hidden]>, from the
wonderful person Geoff Lane <[email hidden]> said

Quoted message said:

Phil Cook said:

>| >I agree with others, your datum in the garmin is still osgb36 when
>| >these mapping programs all seem to use wgs84 and utm.
>|
>| I've checked my Garmin and it shows WGS84
>
>Then reset it to National grid for use in the uk.

However then make sure you feed it positions in OSGB datum. The
easiest way to do that is to feed it positions in Grid Refference form
rather than Lat Long. If you do feed it Lat Long you need to be sure
which Lat Long the position is published in.

If I reset

if you mean 'change the datum/format to WGS84' then yes.. if you mean
'reset', as in 'hard reset', you lose everything, but it's pretty hard
to do that (not even in the manual IIRC)

Quoted message said:

my Garmin will the waypoints I already have in the Garmin
still be valid?

Yes, internally they all store locations as WGS84

Well if you put a waypoint in manually with the receiver set to OSGB36
and then set the receiver to WGS-84 the co-ordinates would change (even
though the actual point is still in the same place). If the co-ordinates
were originally in WGS-84 but were entered manually with the receiver
set to OSGB36 the point would still be in the wrong place :-(

Quoted message said:

.. it's only for input/output purposes that they are willing to try to
translate them into the 1001 different sorts of garbage in use around
the world.

Another wrinkle that I just tripped over and had forgotten about - OS
grid references are always truncated, never rounded.

Depends on who supplies them - we have argued the point here more than
once a while back.

Quoted message said:

Not a problem if you use 10 digit references, but if not then SO12399
45699 turns into a 6 figure reference SO123456 .. about 1.4Km out from
the first one.

~141m actually for a 6 fig ref.

--

Dominic Sexton