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TrekBuddy and Transverse Mercator Maps cal. in OziExplorer
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Joined: 08 Oct 2006
Posts: 4877

PostPosted: Sat Nov 25, 2006 4:14 pm    Post subject: TrekBuddy and Transverse Mercator Maps cal. in OziExplorer Reply with quote

Hello,

I try to use maps which have the following properties:
Map Scale: 2m
Map Datum: WGS84
Map Projection: Transverse Mercator
Central Meridian: 9E

In OziExplorer this map work very good, it is exact +-1 pixel = 2m. When using this map with TrekBoddy it work good in the calibrated corners but in the middle of the map it is of by many meters -> not very usefull for navigation.

Does TrekBuddy only support maps which are 100% rectegular? When you move the curser in the application it looks like this. If you go to the right or left latitude stays the same until the end of the map. Same is true for longitude if you move the curser up and down. It would be nice if TrekBuddy could support this kind of maps, because most of 1:25000 maps are of type Transverse Mercator. If TrekBuddy does not support how to transform the maps? Only putting them with MapCalibrator2 to north is not 100% correct if maps are bigger.

Best Regards,

Rainer
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Joined: 08 Oct 2006
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PostPosted: Sat Nov 25, 2006 4:32 pm    Post subject: Reply with quote

Hi Rainer,

There are two thinks you mentioned.
First - accurancy of WGS84 map in TB. For this, map datum is needed only.
BTW, if you could put this map on rapidshare - we can see.
Second - projection. TB doesn't use projections now, as it is only necessary if you would to check map own grids with OziE grids (no other grids in TB, UTM only).

Ranger
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kruch
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Joined: 02 Jul 2006
Posts: 5662

PostPosted: Sat Nov 25, 2006 6:33 pm    Post subject: Reply with quote

If you guys would enlight me where I can find appropriate formulas, I'll be more than happy to incorporate TM projection support into TB Smile
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PostPosted: Sat Nov 25, 2006 6:50 pm    Post subject: Reply with quote

http://www.posc.org/Epicentre.2_2/DataModel/ExamplesofUsage/eu_cs34h.html

http://www.dmap.co.uk/ll2tm.htm

http://mathworld.wolfram.com/MercatorProjection.html

Ranger
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kruch
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PostPosted: Sat Nov 25, 2006 7:06 pm    Post subject: Reply with quote

I may need it more straightforward Smile

Suppose I know coordinates of map corners, can do lat/lat <-> UTM conversion, and know the map is using TM projection. What do I do? Right now I work with the map as if it is rectangular (trapezoid, to be precise), therefore the error "inside" the map...
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PostPosted: Sat Nov 25, 2006 7:55 pm    Post subject: Reply with quote

Kruch,
You couldn't change easy what is drawn on the map.
There are a lot of people thinking that every map can be used as WGS84.
Wrong. What you see on map picture comes from cartography model used to draw map. So datum is most important. Lat/Lon values depends on used model too.
Projection change nothing on map drawing, gives only another kind of information - grid. TM is just another type of such scale, so if you count x,y position you should use corrections given in TM projection. Thats all.

Ranger
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PostPosted: Sun Nov 26, 2006 10:59 am    Post subject: Re: TrekBuddy and Transverse Mercator Maps cal. in OziExplor Reply with quote

guest wrote:

... If TrekBuddy does not support how to transform the maps?


Rainer,
It is possible to use WGS datum maps with TM in TB without km grid.
Maybe not so comfortable, if you compare phone screen with paper map having km grid only ...
But if no map to test, no case for me.

Regards,
Ranger
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PostPosted: Sun Nov 26, 2006 10:25 pm    Post subject: Reply with quote

Hello Ranger,

what do you mean with > It is possible to use WGS datum maps with TM in TB without km grid.?

What is without km grid? What should I do to the map to make it usable in TB. One way would be to use Grass 6.2 and rectify the TM map, but I dont get this to work. Software and examples in the WWW are not so easy to understand.

To make it more clear what is the problem here a short discription:

I am using a software called NH-TopTrans which you can use to convert different formats (Waypoint, Tracks etc) into other formats. This software can also remote control Google Earth, Magic Maps (TK 1:25000 for Bavaria), TOP 50, Swiss Map etc to extract the map you want. I am using the TK 1:25000 maps, mark the region I what to cover and the rest is done by the software. The resulting map and the *.map file is also generated. When I am using now OziExplorer to read in the map everything works fine. As attachment you get the *.map file. The map is very big 3000x3000 and not so easy to upload. Maybe cal file helps a bit.

When I now slice this map with gimp and tar the resulting set dir and the cal file and load it into the phone, it is of by 100m or so. When I use Map Calibrator 2.01 (MC) and do the cal step manually I see that the map is not north on top. With MC 2.01 you can fix that, but as you know this works only for small maps as TM maps tend to be not rectegular. For small areas this is kind of ok. For jogging, MTB and hiking the TK 1:25000 are the best maps you can get, so thats why I am very interested in getting this thing to work.

By the way I tried the link to Mathematica server were you can find a formula for converting TM map coordinates to lat/lon and vice versa. I tried it to do the calculation with GiNaC and gnuplot to get a TM grid on the screen, but for unknow reasons it not 100% working. I will have to understand it a bit better. Maybe I can extract a correction formula for TB.

Best Regards,

Rainer
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PostPosted: Sun Nov 26, 2006 11:28 pm    Post subject: Reply with quote

Hi Rainer,

Thanks for information about map preparation process you use.
But we should concentrate a little more on map itself.
First. I should know answer for few question.
What kind of coordinates you can find on map itself (visualy) ?
Lat/Lon ? TM ? Grids drawn ? Grid type ? Or no grid, coordinates etc.
I need this graphical info to understand map.

Second. Calibration file. Map can be calibrated in few ways. Which is used for your map? How many points ? What grid shifting ?
Did you have correct info about map source datum ? Was transformed ?
Different tools are producing calibration files differently.

Without such info I could say nothing about your problem.
And easiest way is to see map sample (as little as you can produce).
How you found that error is 100 m ?

I use TM projection maps in TB. If grid was drawn on the map, I don't need TM coordinates at all, I see distance on map grid.

Ranger

Edit:
There is a sample of using Transverse Mercator grid in TrekBuddy
(pictures below).
First of them shows map corner with Lat/Lon and TM(GK) grid(short form) coordinates.
Second shows TM grid scale, it is 2 km grid.
Third shows TM grid in center of map as helpful distance scale.
As you see, Lat/Lon coordinates are used for navigation.
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PostPosted: Thu Nov 30, 2006 9:52 pm    Post subject: Reply with quote

Hallo Ranger and other following the subject,

I have news now. Basically I think I understand now what I made wrong and I think I found at least something which needs an explaination.

When generating my maps, I use the option, while exporting to TB, to use UTM coordinates but the cal file for Ozi *.map used lat/long and a scale of 1.0. I know now this is wrong! When using UTM maps with TB you should use the same coordinates on the map and in the cal file, at least it did it for me. The maps need to be in a format that easting is on the x axes and northing on the y axes, if not maps must be rotated. When generating the *.map file make sure to use it like in this example:

OziExplorer Map Data File Version 2.2
jogging2_01
jogging2_01.bmp
1 ,Map Code,
WGS 84,WGS 84, 0.0000, 0.0000,WGS 84
Reserved 1
Reserved 2
Magnetic Variation,,,E
Map Projection,Transverse Mercator,PolyCal,No,AutoCalOnly,No,BSBUseWPX,No
Point01,xy, 1, 1,in, deg, , ,N, , ,E, grid, , 660983, 5339012,N
Point02,xy, 2681, 2681,in, deg, , ,N, , ,E, grid, , 665992, 5334003,N
...
Projection Setup, 0.000000000, 9.000000000, 0.999600000, 500000.00, 0.00,,,,,
...

You must use grid coordinates and in Projection setup the second parameter has to be the middle meridian of your zone in my case 32U. The scale, next parameter, must be set to 0.9996 and the next the false easting which for UTM maps is 500000m.

When loading that map to the phone TB works very good. Maps resolution is 2m and display +-5m were I could check it.

Now I though well everything fine now lets try something real big and generated a map 16000x13400 pixels and 4m per pixel = (64kmx53.6km). After waiting for gimp to complete this task ( takes forever even with 2GByte Ram Sad. Gimp is not good when using 8 bit file because internaly it use 4 byte per pixel x 2 = 1.6Gbyte and writes all to disk) I use the technic from above but here I got a very suprising result. When scrolling to the map from west to east pressing 5 the northing varies from right (west) 5312013, center 5311932, left (east) 5312011 +11m -72m to 5312000 correct northing, but the easting varies only +-5m? I checked the map again in OziE but 100% correct? Any explaination for that.

By the way I switch from lat/long to UTM and was just using the cursor not the GPS. When using the GPS and corrected the northing by 60m for my part of the map all is 100% correct. When switching from UTM to lat/long no change position stays the same. Any tip what I am doing wrong? I will try to generate a empty map just the grid and try to put it here to show the behavior. You can also try to generate a map 60x50km with 4m per pixel and try it, you should see this behavior.

Thanks,

Rainer

P.S: I will try to do a perl script to cut big files to TB format. I will let you know when ready.
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PostPosted: Thu Nov 30, 2006 10:15 pm    Post subject: Reply with quote

Hi Rainer,

All you stated in first part is OK. Kruch mentioned, that from 095 we will have possibility to use TM(GK) grid coordinates too. To this time don't try to use TM corrections, doesn't work in TB.

Second part. Be carefull with so big maps. Phone is not math operation hero at all, and with bigger maps you will see bigger errors (roundings). Better way is to build atlas with few smaller maps, ie 4000x4000, and one working as preview for them.

Ranger
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PostPosted: Thu Nov 30, 2006 10:42 pm    Post subject: Reply with quote

Hello Ranger,

Ok I will try to make an atlas, even better than the area can be bigger while not having so big files to handle in one part. What is new for me that you can put an overview in a atlas and than change to the details, correct. I will try it on the weekend if there is time.

Anyway I think TB is very good and I hope Kruch will continue his effort to enhance this software to make it even better.

Best Regards,

Rainer
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kruch
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PostPosted: Thu Nov 30, 2006 11:03 pm    Post subject: Reply with quote

Cool info!

My understanding of the issue is (please corrent if I'm wrong):

Good result (+-5m ) is a bit of surprise, because there is no support for TM now and rectangular map is treated as if it represents trapezoid (so it somehow counts with x/y stretching, but very primitively and it has nothing to do with TM distortions), but for small maps even with big scale it may work fine/acceptable.

But with bigger maps, TM maps manifests growing distortion/compression the more the farther you from meridian, and it may differ in easting / northing direction. Couldn't that be your case - bigger error in y direction?

And, here's where TrekBuddy fails. For now.

By the way, how far you are from 9^ meridian?

Now what I did not understand in your post Smile :

Rainer wrote:
When scrolling to the map from west to east pressing 5 the northing varies from right...


Scrolling with 5 from west to east?

Rainer wrote:
When using the GPS and corrected the northing by 60m for my part of the map all is 100% correct. When switching from UTM to lat/long no change position stays the same. Any tip what I am doing wrong?


Why should the position change?

Thanks!
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PostPosted: Thu Nov 30, 2006 11:30 pm    Post subject: Reply with quote

Kruch,
If you see again calibration of map I sent you (wpt case), you find that scale factor is 1.
In teoretical model scale is changing from 0,9996 in central meridian to 1 at the ends of 6 degree sector. It is true, if map content was not transformed.
As I understand, switching 5 is used to see distance to wpt.
BTW, did you read attached links in my last e-mail ? All 39 pages ?

Ranger


Last edited by guest on Thu Nov 30, 2006 11:45 pm; edited 1 time in total
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kruch
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PostPosted: Thu Nov 30, 2006 11:45 pm    Post subject: Reply with quote

guest wrote:
BTW, did you read attached links in my last e-mail ?

Ranger


Last email from you that I can see in my inbox is dated 2006-11-16 and there are no links attached it... ?
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