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map calibration file
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Sun Feb 14, 2016 11:10 am    Post subject: Reply with quote

Ranger wrote:
Do you have grid lines on map pictures ?

On some zoom levels at least there are. Not marked with values, though, as far as I can see.
The source is:
https://kso.etjanster.lantmateriet.se/

They released (free into public domain) a lot of data and some is freely available through a WMTS service, but only in SWEREF99TM projection (same as using UTM zone 33 for the whole of Sweden)

I can make MOBAC download the tiles, but since it expects spherical mercator projection, the calibration files are wrong...
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Sun Feb 14, 2016 11:16 am    Post subject: Reply with quote

Gmi format rather couldn't help, it is based on Lat/Long values only and wasn't used for tiled maps mostly.
If you can download tiles, you can probably save expected area as PC format in Mobac (graphic file and calibration) and than recalibrate maps using ie known grid coords, if needed. In TB calibration is needed for whole used map, not for one or few tiles.
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Sun Feb 14, 2016 11:37 am    Post subject: Reply with quote

Ranger wrote:
Gmi format rather couldn't help, it is based on Lat/Long values only and wasn't used for tiled maps mostly.

That is a pity...

Ranger wrote:
If you can download tiles, you can probably save expected area as PC format in Mobac (graphic file and calibration) and than recalibrate maps using ie known grid coords, if needed. In TB calibration is needed for whole used map, not for one or few tiles.

Yes, this is exactly what I have been doing, but am now trying to automate the process, because it becomes quite tedious if you have to do more than a few...
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Sun Feb 14, 2016 12:31 pm    Post subject: Reply with quote

Have you ? Smile
This year we will have 10 Years of TB & Forum Anniversary. A lot of time for hobby works Cool Laughing
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Sun Feb 14, 2016 12:51 pm    Post subject: Reply with quote

Ranger wrote:
Have you ? Smile

Yes, but I was not using OziExplorer. I was calculating Northing and Easting from the tile numbers, then using an online converter to convert to WGS84 lat/lon and pasting those values directly into the .map files...
Quite cumbersome


Ranger wrote:
10 Years of TB & Forum Anniversary
Still the best app for sailing navigation Cool
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Sun Feb 14, 2016 12:57 pm    Post subject: Reply with quote

Short process, indeed Wink
Yep, the best for my needs too Cool
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kruch
Site Admin


Joined: 02 Jul 2006
Posts: 5676

PostPosted: Sun Feb 14, 2016 1:46 pm    Post subject: Reply with quote

JNT wrote:
So the MMPLL lines must also be there? Do they have to give lat/lon values?


Unfortunately yes.

In fact, I just checked, shortened map format used for built-in world map only works because it uses lat-lon in PointXY lines, otherwise it would not work. And also because it uses default WGS 84 datum and does not need projection setup parameters. Sad
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Thu Feb 18, 2016 6:47 am    Post subject: Reply with quote

Since trekbuddy is using only the 4 corner points and they have to be lat/lon, does it use linear interpolation to determine the values in the center?

In my case the map is linear in meters, but definitely not linear in lat/lon, so of course it would be best if the northing and easting values could be used directly.
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Feb 18, 2016 10:34 am    Post subject: Reply with quote

Used directly where ? Smile
Case is simple, TB supports popular kind of calibration files, not some kind of calibration points in unknown structure.
To follow rules described on forum, it is just enough to use such kind of tool as is, all calibration data used by app are included in file.
Or you just asking indeed about new TB calibration file format, where part of info you have is included in OziE calibration container? For what you need it ?
I'm just lost Smile
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Thu Feb 18, 2016 11:06 am    Post subject: Reply with quote

To clarify. I am downloading tiles from a wmts. These tiles are in Sweref 99TM projection, so the coordinates are in meters North and meters East. Easily calculated from the zoom level and tile numbers.
Unfortunately mobac cannot handle anything other than spherical Mercator. It is trivial to make it download the tiles, but of course it creates the wrong calibration files. So now I'm changing the code of the atlas creator part to create the correct calibration file. But (and this is a big but) trekbuddy cannot handle a reduced calibration file in Sweref 99TM. (This is a piece of cake to produce with mobac.) So I have to convert meters to lat/lon values (not trivial). I can then make mobac write the lat/lon values of the corners, but of course these lat/lon values are not linear over the tiles. Therefore my question. Smile
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Feb 18, 2016 11:47 am    Post subject: Reply with quote

Yep I know what kind of service you use, so it is clear what you have Smile
Shortly, you have coordinates, visible in tiles names as coded in Sweref 99TM, so you can easy have 4 needed calibration points in this grid.
But you don't like to use for calibration any coords calculator available, to ie recalculate them back to WGS84(GRS80) lat/long. Clear.
It just means, that you can't follow OziE calibration file container, where both grid and lat/long values are used in it.
Something like "reduced OziE container" just doesn't exists, means other calibration format is needed.
TB is just known calibration format receiver, not calibrator itself Wink
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Thu Feb 18, 2016 12:54 pm    Post subject: Reply with quote

Well, as I understand (correct me if I'm wrong) OziExplorer uses the list of points (lines 10 to 39), together with the datum and projection parameters (lines 5, 9 and 40) to actually calibrate the map.
The lat/lon values (MMPLL points of lines 50 to 53)are not used for calibration but only to know where in the world the map fits.
I'm not sure how accurate calibration can be when using only the corner points of an area for which these values are non linear. Confused
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Ranger



Joined: 12 Dec 2006
Posts: 6030

PostPosted: Thu Feb 18, 2016 1:18 pm    Post subject: Reply with quote

There are indeed two sections Smile
First section shows calibration way, where calibration points can be placed inside map pict at different positions, not only in corners.
Second section (map usage section) where OziE calculates values for map corners as MMPNUM, MMPLL.
Calibration points can be grid as well as lat/long for first one, but MMPLL for second are lat/long only (see calibration sample on previous page).
Don't worry what is linear or not, every app handling such maps and coords must support calculations for both coords types Wink TB does Smile
Just see sample, third map is in PL-1992 (old name PUWG 1992), very similar to SWEREF 99 TM, used in such coordinates system.
Doesn't matter how you calibrate it, works in both coordinates types. Source topic:
http://www.trekbuddy.net/forum/viewtopic.php?t=6748&start=4

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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Thu Feb 18, 2016 2:57 pm    Post subject: Reply with quote

Well, I am a little worried... Wink

If I take the following corners: (Easting , Northing)
Code:
581760.00   6607648.00
602240.00   6607648.00
602240.00   6587168.00
581760.00   6587168.00


The Karney method gives (WGS84):
Code:
59.59902238°N, 016.44840409°E
59.59451130°N, 016.81102408°E
59.41069339°N, 016.80119987°E
59.41517166°N, 016.44054510°E


OziExp gives:
Code:
MMPLL,1,  16.448404,  59.599022
MMPLL,2,  16.811095,  59.594510
MMPLL,3,  16.801268,  59.410657
MMPLL,4,  16.440544,  59.415136


Snyder (?) equations gives:
Code:
16.447922231,   59.599027709
16.810421710,   59.594519623
16.800583771,   59.410701886
16.440052263,   59.415177098


Perhaps it is accurate enough, but my preliminary tests show that I am about 30m off compared to a known point...
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JNT



Joined: 10 Jan 2009
Posts: 416
Location: Sweden

PostPosted: Thu Feb 18, 2016 3:29 pm    Post subject: Success! Reply with quote

Finally success! Very Happy

I have to use the Karney equations (http://www.movable-type.co.uk/scripts/latlong-utm-mgrs.html) (http://arxiv.org/pdf/1002.1417.pdf) and I have to use these corners to calculate the Nothing and Easting values to convert to lat/lon (WGS84), then I am getting the correct position compared to a known point.

(Now I just have to find or write(Shocked) a java implementation of these equations...)



2016-02-18.png
 Description:
Corners
 Filesize:  253.07 KB
 Viewed:  7715 Time(s)

2016-02-18.png




Last edited by JNT on Thu Feb 18, 2016 3:52 pm; edited 1 time in total
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