X: 500000m Y: 400000m appear to be the coordinates of center of map, and not Lat53.4872,Lon0.4944 (near)

Grid ref uses 3 first digits of x,y coordinates, by example, for a coordinate X: 505000m Y: 404000m,

grid = TA 050 040

Solved

Posted on 2005-05-04

Hello

I am new to GIS and I desperately need some help.

I am creating a very basic tracking application and I use a GPS receiver which produces latitude and longitude coordinates.

I am using Navteq streets data and this uses the following projection:

datum: osgb_1936

ellipsoid - airy

I need to convert my latitude and longitude coordinates into the appropriate format for this map. I do not know what format this is. I have tried converting to UTM and that does not give me the right answer.

When i view a location on multimap this shows you the latitude and longitude coordinates for the location and some x,y coordinates. An example is shown below...

Location: United Kingdom

Grid ref: TA000000 Postcode district: DN21 4xx (map centre)

X: 500000m Y: 400000m

Lat: 53:29:14N (53.4872) Lon: 0:29:40W (-0.4944)

Web Address: www.multimap.com/map/browse.cgi?lat=53.4872&lon=-0.4944&scale=2000000&icon=x

I need to be able to convert my latitude and longitude coordinates into those x, y values in meters as that is what my map or my map software seems to use. I do not understand why but when i plot those x and y values on my map they come up at the right place.

Please can you tell me what system of projection those x,y coordinates are based on. Please can you also tell me a resource for converting between the two programmatically. I need the conversion to be very accurate. I am willing to pay. I need to be able to make the conversion from a vb.net program.

Thank-you very much for your help. This is an urgent problem.

Thanks

Andrea

I am new to GIS and I desperately need some help.

I am creating a very basic tracking application and I use a GPS receiver which produces latitude and longitude coordinates.

I am using Navteq streets data and this uses the following projection:

datum: osgb_1936

ellipsoid - airy

I need to convert my latitude and longitude coordinates into the appropriate format for this map. I do not know what format this is. I have tried converting to UTM and that does not give me the right answer.

When i view a location on multimap this shows you the latitude and longitude coordinates for the location and some x,y coordinates. An example is shown below...

Location: United Kingdom

Grid ref: TA000000 Postcode district: DN21 4xx (map centre)

X: 500000m Y: 400000m

Lat: 53:29:14N (53.4872) Lon: 0:29:40W (-0.4944)

Web Address: www.multimap.com/map/brows

I need to be able to convert my latitude and longitude coordinates into those x, y values in meters as that is what my map or my map software seems to use. I do not understand why but when i plot those x and y values on my map they come up at the right place.

Please can you tell me what system of projection those x,y coordinates are based on. Please can you also tell me a resource for converting between the two programmatically. I need the conversion to be very accurate. I am willing to pay. I need to be able to make the conversion from a vb.net program.

Thank-you very much for your help. This is an urgent problem.

Thanks

Andrea

17 Comments

X: 500000m Y: 400000m appear to be the coordinates of center of map, and not Lat53.4872,Lon0.4944 (near)

Grid ref uses 3 first digits of x,y coordinates, by example, for a coordinate X: 505000m Y: 404000m,

grid = TA 050 040

first two letters on grid are related to first digit on x/y coordinate, by example, for a coordinate 499000m Y: 399000m

grid = SK990990

http://www.36haroldstreet.

http://www.bangor.ac.uk/is

But I don't have clear what do you want to do:

You receive your data from GPS in latitude/longitude format

You want to display it in some format, but I think you don't need to convert it to X,Y, just to change datum from stardard WGS-84 (what GPS output) to OSGB-1936 (latitude/longitude)

continues....

What you need are the correct indexes values for OSGB-1936. Them are:

SPHEROID = Airy 1830

Equatorial radius = 6377563.396,

Flattening = 1 / 299.3249646

Prime meridian = 0

0.0174532925199433 degrees

EPSG Code = 4278

Or, described with reference to WGS-84

Ellipsoid, Delta a, Delta f (* 10^4), Delta X, Delta Y, Delta Z.

Airy, 573.604, 0.11960023, +375, -111, +431

http://home.hiwaay.net/~ta

But first, I want to know, how do you want to translate your data (from datum x to datum y)

http://www.itc.nl/ilwis/do

Thank you very much for your replies. However, I am not sure I understand them. In fact, I am not sure I understand my own problem but I am trying!!

I know that I have a GPS receiver which gives me latitide and longitude values. I know that these values are not in the same format/projection (i don't know what the correct term is) as my map.

The x / y values that multimap shows seem to be correct for my map. I believe I need to convert my gps latitude and longitude co-ordinates into ordinance survey grid coordinates and that these look like the x/y values on multimap.

I do not know what a datum is. I know that gps uses WGS-84 and OS uses OSGB-1936.

I need to be able to convert very accurately from gps to ordinance survey. I have found this link which tells me I need to use OSTNO2

http://www.gps.gov.uk/gpss

I want to make sure that I am performing the right conversion.

I am using GPS data and i want to be able to plot points on Navteq streets data which uses OCGB-1936. I need to find some software/library to convert my latitide and longitude values so they can be plotted on my map.

I hope that is clearer.

Thanks

Andrea

> and longitude co-ordinates into ordinance survey grid coordinates and that these look like the x/y values on

> multimap.

This is not necessarily true. Maybe your map application shows X,Y values, but, how do you pass information to it? X/Y or lat/long? do you have a sample code portion?

>I do not know what a datum is. I know that gps uses WGS-84 and OS uses OSGB-1936

In plain words, there are little difference (some meters) on how to name the position of an object in the earth, that depends on which values you have considered to measure de earth (equatiorial radius, flattening factor, etc). Every group of coefficients is called a datum. Today almost use a unique datum valid for all the world: WGS-84, but once upon a time, every country had its own datum.

So, please give me some details on your library's functions to help you better.

I use aspmap. I simply create a map object and then create a callout object which basically puts a little call out graphic at a certain point on the map. I have to set the x/y coordinates of the callout. If i set the x/y coordinates to be the values to be the values I get from multimap it puts the callout at the right place on the map.

Set Map = Server.CreateObject("AspMa

Set Point = Server.CreateObject("AspMa

point.x = 387900

point.y = 341500

callout.X = point.x

callout.Y = point.y

callout.Text = "You are here"

If i use these coordinates it puts a callout on the map where i want it to (somewhere in stoke on trent). The gps latitude and longitude that my receiver gives is approximately 52n and -2w. I need to know how to get from the latitude and longitude to the x and y values as shown above and as used on multimap.

Thank

Anyway, it is really hard to find in the internet some algorithms to transform WGS Lat/Long to OSGB Grid (x/y)

I have found this:

http://www.bangor.ac.uk/is

But it requires that Lat/Lon datum is OSGB and not WGS-84, so you have to:

1)Make datum transformation, from WGS-84 to OSGB (Airy) datum. Data will be still lat/lon

2)Then, these lat/lon values will be the input for this algoritm that will convert to OSGB Grid coordinates

Here is a ready made program to test second part.

http://www.russ-hore.co.uk

So review your documentation to avoid all these headache.

BTW, what software are you using? I know data is from NavTeq, but which ASP component, maybe ASPMap from VDS Technologies?

I am using ASPMap fron VDS. I seem to have found one way to solve the problem.

My original navteq maps were in OSGB projection. I now have copies of the maps in WGS-84 projection and they allow me to plot latitude and longitude coordinates.

Do you know ASP Map. I would like to be able to simply plot my latitude and longitude values on a map in OSGB projection but it does not work. As I said, it works fine when my map is in WGS-84 but not OSGB

Andrea

check out this link.

http://jan.ucc.nau.edu/~cv

the basic math behind the conversion of latitudes and longitudes in to linear distance is also available in the link.

The proj library itself is obtainable from http://proj.maptools.org/

hope this helps.

--matt

By clicking you are agreeing to Experts Exchange's Terms of Use.

Title | # Comments | Views | Activity |
---|---|---|---|

GeoCode - how to set a pushpin? | 8 | 332 | |

How do I get a functional KML file to display on GoogleMap API v3 | 2 | 641 | |

Android App to Selectively Hide or Disable GPS? | 4 | 285 | |

Google Maps | 2 | 109 |

Join the community of 500,000 technology professionals and ask your questions.

Connect with top rated Experts

**10** Experts available now in Live!