Bílý vrch
icon TrekBuddy
www.trekbuddy.net
Outdoor companion.
  • internal / bluetooth / simulator GPS
  • offline raster maps
  • smart GPX / raw NMEA logs
  • waypoints and simple navigation
  • custom views
  • MIDP and Symbian phones
  • Blackberry
  • Android
Visit wiki to see all features, guides and howtos. Project tracker.
Trekbuddy is on Github now

Partners:    (Polish/Polski)(Polski) Compass mapy      (Polish/Polski)(Polski) Galileos mapy      (Polish/Polski)(Polski) CartoMedia      (Czech/Èesky)(Èesky) Eaglesoft trasy      (Polish/Polski)(Polski) ExpressMap     

 FAQFAQ   SearchSearch   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
RT90 maps and coordinates
Goto page 1, 2, 3  Next
 
Post new topic   Reply to topic    TrekBuddy Forum Index -> Recycle Bin
View previous topic :: View next topic  
Author Message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Wed Jan 10, 2007 6:48 pm    Post subject: RT90 maps and coordinates Reply with quote

I have this digital map I bought some years ago from Lantmäteriet (the swedish cartographic agency). It came as an image with a calibration file that is recognized by OziExplorer when importing it as DRG.

After importing it in OziExplorer I can add waypoints by coordinates and they end up in the right place. When I use the map in trekbuddy (0.9.5b2 - rc3) however they end up at least 100 meters away.

I have found a document at Lantmäteriets website explaining that the lat/long coordinates of an RT90 map can differ several hundred meters from WGS84/SWEREF99. This seems to be conclusive with what I can see in both OziExplorer and trekbuddy. In OziExplorer the coordinates shown in the bar are wrong unless I explicitly tell it to show coordinates in WGS84. Then they are correct.
Well of course... Wrong is a relative term but since the GPS speaks WGS84 and geocaches are also located in WGS84 any other coordinates are quite useless. At least to me.

In the image Oziwpt I've shown the location of a geocache near me. Waypoint 1 is entered in WGS84 and it is correct. I've been there so I know. Waypoint 2 use the same coordinates but in RT90 and is some 100 meters off. I made the screenshot with the pointer resting on the real cache location but with the bar showing coordinates in RT90 instead of WGS84. Comparing the coordinates with the ones in the trekbuddy screenshot one can see that trekbuddy also shows the RT90 coordinates. Changing the coordinates in settings has no effect.

I've checked the .map file that is generated by Ozi and the coordinates are expressed in RT90 lat/long. I've tried manually hacking up a .map file with the real WGS84 coordinates as well. I got it working in Ozi but I had the same error in trekbuddy?! (is my k800i caching files perhaps?)

I've been fiddling with this for about three weeks now and I'm at a loss. Does anyone else have any experience with swedish maps?



Oziimp.png
 Description:
Importing a map with a calibration file as DRG in OziExplorer
 Filesize:  4.62 KB
 Viewed:  34326 Time(s)

Oziimp.png



Oziwpt.png
 Description:
Waypoint 1 shows the location of a geocache at N57° 39.289 E11° 56.449 in WGS84. Waypoint 2 shows the same coordinates entered in RT90. The coordinates in the bar show the RT90 coordinates at the cache location.
 Filesize:  70.61 KB
 Viewed:  34326 Time(s)

Oziwpt.png



trekbuddy_SonyEricsson_K750_5.png
 Description:
The waypoint entered in trekbuddy. The crosshairs are placed at the real cache location. The coordinates shown in the OSD are obviously RT90 and not WGS84. Otherwise they would have been close to N57° 39.289 E11° 56.449
 Filesize:  23.54 KB
 Viewed:  34326 Time(s)

trekbuddy_SonyEricsson_K750_5.png


Back to top
View user's profile Send private message
kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5673

PostPosted: Wed Jan 10, 2007 7:10 pm    Post subject: Reply with quote

When you load such a mpa in TB, what datum and projection setup do you see in Options->Info->Map?
Back to top
View user's profile Send private message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Wed Jan 10, 2007 8:14 pm    Post subject: Reply with quote

This is what the infoscreen shows


info.png
 Description:
 Filesize:  2.89 KB
 Viewed:  34314 Time(s)

info.png


Back to top
View user's profile Send private message
kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5673

PostPosted: Wed Jan 10, 2007 8:30 pm    Post subject: Reply with quote

Did you enter WGS84 coordinates for wpt 1 in trekbuddy?
Back to top
View user's profile Send private message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Wed Jan 10, 2007 9:01 pm    Post subject: Reply with quote

Yes I entered these coordinates: N57° 39.289 E11° 56.449. All the waypoints are entered using those numbers.
Back to top
View user's profile Send private message
kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5673

PostPosted: Wed Jan 10, 2007 10:36 pm    Post subject: Reply with quote

Confused ... if you position the crosshair to intended wpt position, press "1" and select Enter Custom, what lat/lon trekbuddy fills in?
Back to top
View user's profile Send private message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Wed Jan 10, 2007 11:28 pm    Post subject: Reply with quote

If I move the crosshairs to the correct waypoint location I get the same coordinate in the OSD as I get in OziExplorer in RT90 over the correct waypoint location. The OSD shows N57° 39.309 E11° 56.590. If I however choose to add a custom waypoint at the location the prefilled values are N57° 39.32743 E11° 56.54486.
Back to top
View user's profile Send private message
Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Jan 11, 2007 11:00 am    Post subject: Reply with quote

Hi,
Since I didn't use Swedish maps, so couldn't check your case exactly.
But if you use RT90 map, you should use RT90 coordinates on map.
Setting WGS84 coords point as RT90 doesn't make sense, because it is really another point,
you can only see map position difference between RT90 and WGS84 for the same Lat/Lon values of point.
Next is entering waypoint coordinates in TB. As I know, always is in WGS84, excluding one case.
If you have non WGS84 map and use Enter Custom, coords are converted from map coords to WGS84.
There is a one additional problem, pixel map resolution decides about wpt coords values accurancy,
so it isn't easy to have the same coords when switching between maps. But in my opinion TB should try to show
the same point on maps, not the same coords. It works this way only with GPS provider on.

So what can I say ? Just use external converter to see RT90 coords of your WGS84 wpt.
This way you be sure about wpt coords values for your map. Next set the wpt in TB using WGS84 coords
and compare position of wpt marker with RT90 coords in OSD, moving crosshair to this point.
You will have an answer what is wrong, wpt coords or wpt marker position. If any.
Back to top
View user's profile Send private message
kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5673

PostPosted: Thu Jan 11, 2007 11:23 am    Post subject: Reply with quote

FYI, I'm using Molodensky datum transformation. Maybe 7-parameter Helmert would yield better results for us? But i doubt it is the problem here...
Back to top
View user's profile Send private message
Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Jan 11, 2007 11:45 am    Post subject: Reply with quote

kruch wrote:
FYI, I'm using Molodensky datum transformation. Maybe 7-parameter Helmert would yield better results for us? But i doubt it is the problem here...


Not easy question. Counting accuracy is one, but second is map itself accuracy, GPS precision, way of transformation for different datums etc. Molodensky isn't too bad Very Happy
I have no info what is in TB to say exactly.
Back to top
View user's profile Send private message
kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5673

PostPosted: Thu Jan 11, 2007 11:57 am    Post subject: Reply with quote

Ranger wrote:
Not easy question. Counting accuracy is one, but second is map itself accuracy, GPS precision, way of transformation for different datums etc. Molodensky isn't too bad Very Happy


Ranger, I was just about to write that I realized that you and me we are OK maybe because S-42 maps we use have much less dx/dy/dz than RT90, but now i can see that PND1925 is also Bessel 1841 and thousands of meters shift to WGS, similar to RT90... and they work for you, right? So... dead end Confused Smile
Back to top
View user's profile Send private message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Thu Jan 11, 2007 12:04 pm    Post subject: Reply with quote

-> kruch
Yes I've seen tips on the "Lantmäteriet"-website about 7-point transformation beeing more accurate. There is a page there describing how to set it as a manual transformation in Garmin GPS receivers for better accuracy. I don't quite understand how it works though.

-> Ranger
I'm not sure I follow your reasoning completely som maybe I'm answering something that you didn't say or I'm breaking down open doors. Sorry about that then but here goes.
Yes the map I've got is an RT90 map. All swedish maps are. The thing is, I'm actually quite confused by the use of Lat/Long in RT90. You never specify coordinates in Lat/Long in RT90. You always use grid coordinates. I was very confused by OziExplorer first since it seems to deal only in Lat/Long.
When I import the map in OziExplorer it interprets the accompanying calibration file that specifies the top corner in RT90 grid coordinates and the pixel size. I then have a calibrated map in OziExplorer that is correctly positioned in RT90. The RT90 Lat/Long are of course not the same as WGS84 Lat/Long. Even more so the RT90 Lat/Long are really useless since you want to specify RT90 coordinates in grid format. The thing is though that in OziExplorer I can just select that I want to display coordinates in WGS84 instead. Then the coordinates displayed makes sense in a GPS application.

The thing is that since I'm mostly using GPS for geocaching only WGS84 will do for me. If I'm out in the forest hunting a multicache I do not want to have to do 7-point coordinate transformations in my head to be able to place the next waypoint in the right location Wink
Back to top
View user's profile Send private message
Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Jan 11, 2007 12:25 pm    Post subject: Reply with quote

Sorry, but I see here few misunderstandings.
First, you have source wpt coords in Lat/Lon for waypoint. Coords from GPS are in WGS84 Lat/Lon too. But you decided to use map with different datum and coords system. So the question is how to show such coords on different map.
Second. To show where you are and where you would be there are two ways:
- convert GPS and wpt coords to km grid directly;
- convert the same coords to map Lat/Lon;
The way depends, how you set coords in TB. As I can see your TB picture, Lat/Lon is used. So my answer was based on yours pictures and info.
Third. Could you have wpt coords in Swedish grid ? If yes, switch TB to map grid coords and you can see problem as you wrotes.

@Kruch. Molodensky errors are estimated as "in meters/ten of meters". But for better precision in rotated datums 7p is a way. Helmert have "not mathematical" direction of rotation, as some US geodesist says Wink


Last edited by Ranger on Thu Jan 11, 2007 12:51 pm; edited 1 time in total
Back to top
View user's profile Send private message
Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Jan 11, 2007 12:43 pm    Post subject: Reply with quote

kruch wrote:

Ranger, I was just about to write that I realized that you and me we are OK maybe because S-42 maps we use have much less dx/dy/dz than RT90, but now i can see that PND1925 is also Bessel 1841 and thousands of meters shift to WGS, similar to RT90... and they work for you, right? So... dead end Confused Smile


Yes, PND1925 works for me now, similar as in OziE. No problem.
Back to top
View user's profile Send private message
marmeladburk



Joined: 31 Dec 2006
Posts: 20

PostPosted: Thu Jan 11, 2007 12:52 pm    Post subject: Reply with quote

uhm.. ok...
But all swedish maps are in RT90. Shouldn't I still be able to use them in trekbuddy with a GPS? I can use them in OziExplorer and Fugawi with no problem. After calibration I just choose WGS84 for coordinate system and the application converts everything for me.

I tried once to hack up my own .map file for the map by converting the grid coordinates in the corners to WGS84. The problem then was that I couldn't get trekbuddy to understand that it should still use the swedish projection. Maybe I did something wrong there. Well I actually got the .map file to work in Ozi correctly as WGS84 with swedish projection. Something is fishy Wink
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    TrekBuddy Forum Index -> Recycle Bin All times are GMT
Goto page 1, 2, 3  Next
Page 1 of 3

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum


Powered by phpBB © 2001, 2005 phpBB Group