GPSFS, Java and some troubles

August 31st, 2007, 21:05 Posted By: matrix681

Hello,

im writing a little programm with java, where i want to see my position on a map.
so i decide to use GMDL.

first i have to thank for this great tool :thumbup:
i also have to thank for the detailed description of GPSFS at the end of the sourcefile
(but there seems to be a little error. there says, that the IDX begins with the highest zoom level, but it begins with the lowest zoomlevel )



however, i now can draw the map at my current position. but i have trouble with the exact positioning on the drawed map.

for better understanding a little example:
My GPS-Position is: 48.3767 16.2426

if i search this coordinates on maps.google.com i get the exact position on the freeway:
http://maps.google.com/maps?f=q&hl=e...wloc=addr&om=1

but if i draw the map on my own, im a little bit outside or on the border of the freeway:
http://stud3.tuwien.ac.at/~e0025170/...s_position.jpg


i don't know much thing about the projection. i just 'translate' the code to get the gps-position of the downloaded map from the X-Y pair from the sourcecode of mapthis.
(getLatLong, getTileCoord, initLatLong)



Any idea, why the position could be not exact?

I do following to compute the position on the map:

1) i compute the coordinates of the upper-left and the lower-right corner of the image:


2) i find the 256*256 part, where my incoming GPS-Position is and draw it, with the surrounding parts in a 768*768 image.

3) i compute the position in this little image, and get a 300*300 pixel part of it.

4) my position should now be exact at the center of this 300*300 pixel, but it's not





sorry for my bad english and thanks in advance,
Ahmet Y.

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