[mkgmap-dev] What's d for? (possibly related to clipping issue?)

Mon Feb 23 07:49:30 GMT 2009

>> Why does the line clipper add a tiddly amount (d) in these expressions? 
>>
>>
>> 		double d = 0.00001;
>> 		if (t[0] > 0)
>> 			ends[0] = new Coord((int) (y0 + t[0] * dy + d), (int) (x0 + t[0] * dx + d));
>>
>> 		if (t[1] < 1)
>> 			ends[1] = new Coord((int)(y0 + t[1] * dy + d), (int) (x0 + t[1] * dx + d));
>>     
>
> It for rounding to the nearest map unit.  I remember I was just adjusting
> it until I got something that worked, but can't quite remember what the
> problem I was solving was.
>
> If I'd thought about it more I would have said that the correct value would be:
>
>   360/(2 * 2^24)
>
> which comes to 0.000010728, so perhaps close enough.
>
>   
>
Sorry for my answer from yesterday, there is a fault in it. I've thought 
about it again and think your explanation is wrong.
In this case the rounding by 0.0001 makes no sense, as the x and y 
values are already in internal units, not in degrees. So if you want to 
round the values, you have to add/subtract 0.5!