[mkgmap-dev] help needed

Wed Jul 30 16:42:47 BST 2014

Hi all,

I am still trying to find a better solution for the problem
posted by Roger Calvert:
http://gis.19327.n5.nabble.com/Incorrect-compilation-of-grid-lines-tp5809502.html

We are using some approximations to speed up calculations,
most of them work fine as long as distances are rather short.

On the other hand, mkgmap doesn't check if distances are short,
so in some cases we have rather large errors.

I found two sources for formulas:
http://www.movable-type.co.uk/scripts/latlong.html
and 
http://williams.best.vwh.net/avform.htm

The latter gives an example to verify the code. I've coded
some lines in Java and got similar results as in the "worked example".
I've then tried to verify the example in JOSM,
esp. the cross-track-error.
Unfortunately, when I try to draw a (nearly) perpendicular
line from point A to line LAX-JFK, JOSM says the line is ~27.7 km 
long, while the example calculations are near 13.8 km or
about 50% of the JOSM value.

What am I getting wrong?

Gerd

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.mkgmap.org.uk/pipermail/mkgmap-dev/attachments/20140730/ad5cdc40/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: JFX-LAX.osm
Type: application/octet-stream
Size: 765 bytes
Desc: not available
URL: <http://www.mkgmap.org.uk/pipermail/mkgmap-dev/attachments/20140730/ad5cdc40/attachment.obj>