Differences in Map co-ordinates

Discussion in 'GPS Use, Tracks & Maps Discussion' started by tonykiwi, Apr 11, 2009.

  1. I am working with Mapsource Thailand map 8.1 and also using Google earth for locating junctions etc.

    I am constantly finding that when I locate a specific junction on Google earth (which I can clearly see as being there) I create a waypoint on mapsource using the GE co-ordinates however the waypoint ends up somewhere else. The co-ordinates I am putting in are the same however it seems that there is a discrepancy on one or the other of the programs.

    The resulting waypoint is in the general area however todays was about 1.5 kms away form the junction once I had freated the waypoint.

    Anyone found this for themselves? Which is accurate as far as map co-ordinates are concerned.

  2. It is well known that Google Earth in many areas does not show the exact location with difference raging from +/- 0-100 meters or so.

    As you see difference of 1.5 km there must be something else wrong. Most probably this is a map datum issue. The Thailand map uses the WGS 84 datum. Check in Mapsource under Edit / Preference / Position if Mapsource has been set to WGS 84. New Zealand uses a different datum (NZGD 49 or NZGD 2000) and this may be the reason that you find differences in the exact location.
  3. Thanks for that

    I have checked the datum and it is correctly showing as WGS 84

    I am not too sure if you use the same Thailand map as me but if you do, here are the coordinates I have. A check against Google earth and Mapsource map may show where I am going wrong.

    Coordinates I took from Google earthm= 18°55'6.69"N 98°54'47.37"E

    Coordinates I put into Mapsource = N18 55.669 E98 54.474

    Google earth takes me to a junction (the junction I want to find) but Mapsource takes me elsewhere


  4. Tony,

    Just checking, your first set of coordinates seem to be in degrees, minutes and Seconds (divisible by 60) and the second set in decimal.

    It isn't as easy as that.

    Can you put the Degrees and Minutes into Mapsource???

    Otherwise you might need to convert everything.


  5. Hi there

    Thanks for that. They sure don't seem to want to make this easy do they!

    I have tried that and the result I got through the converter didn't help so I will keep working on it. I did not think about the difference between the two methods, I just thought they both meant the same

    Hope all is well in your world


  6. Tony,

    On the same page in Mapsource as where you set the Map datum you can also set the Units - you have 3 choices "Degrees" or D, "Degrees and Minutes" or D/M and "Degrees, Minutes and Seconds" or D/M/S.

    Your Google Earth coordinates are in D/M/S while your Mapsource coordinates are in D/M and this causes the difference in location.
  7. Thanks Auke

    I presume you mean the upper dropdown menu "Grid"

    It is presently set for Lat/Lon hddd(small diamond but I can't replicate it here)mm.mmm'

    The next one in the dropdown is similar

    Lat/Lon hddd (diamond)mm'ss.s"

    I have tried changing between the two butwhen I paste the Google earth formatted coordinates intothe waypoint on Masource it will not accept it and shows an error.

    Am I setting the correct Units' as per your advice? The Units tab does not have such a change available

    If not what do I do to put it right

    Once done, what format should the coordinates be in to take me to the road junction

    The beers I owe you are stacking up


    Ps I am using version 6 15 4 for Mapsource
  8. Sorry, I was in a bit of hurry this morning so my reply may not have been clear. Here is the screen shot of the Lat/Long options in Mapsource . The first is in full degrees, the second in Degrees and Minutes and the third are Degree, Minutes and Seconds


    The coordinates of N18 55.669 E98 54.474 you had put in Mapsource are in Degrees Minutes or hddd mm.mmm . With this waypoint still on the same place, the coordinates will become N18.92782 E98.90790 when you change the Grid to Degrees (hddd.dddd) and N18 55 40.1 E98 54 28.4 in case you change the Grid to Degrees Minutes and Seconds (hddd mm ss.s).

    Hope that this will make it more clear. If not just PM me.

    Attached Files:

  9. In conclusion, many thanks to Auke for guiding me through this. For anyone who is as novice as me, here is the resoution.

    In Google earth I changed the preferences to the one shown in Aukes screen dunp. I also changed to the same setting in Mpsource and everythig came right.

    These changes do not apear to have affected the waypoints and POI's I had already placed into Mapsource under the old system

    Thanks all

  10. Another thing to watch is the age of the imagery. I have noticed on older satellite imagery used in GE that my waypoints would be off. When a newer image has been uploaded into GE by the imagery gods I have noticed the accuracy improve. I only use GE to visually scout out an area and use the coordinates there as a rough guide. Sometimes I have access to very updated imagery not related to GE and there are differences, so I would only use them as a guide, correct in mapsource and as long as your gps is in a non-offroad mode you should be good to go accuracy wise.
  11. Thanks Eric, the different quality of map sets on Google earth can also make things difficult. I have found that town/village locations on GE are not always accurate. For instance, Sameong is in a totally different place to Davids map and mapsource. Having said that, version 8.1 differs sometimes from Davids map too. I am using the criteria that davids map is more up to date, however it has no gridreferences. That is where I use GE and mapsource to create my own waypoints. I have found some by following the road shape and identifying the correct positions of junctions etc.

    I have also used some waypoints from Beddhist and Christian to identify places properly on 8.1.

    In the final analysis though, I am sure that all this planning is not going to actually mean a thing because everything will change when I get there and am sure to be advised differently :) That is the fun of the 'journey'



Share This Page