Re: Length of a PolyLine

[Hans Breuer <hans breuer org>]

Chris Burkert wrote:
> Hi List,
>
> at first I would like to thank all of you developers of dia.
>
> I'm using dia for drawing maps where I take some raster data like a 
> .png, put some lines and labels on it and export this as a .png again. I 
> have an example at [1].
>
> Now I would like to measure the length of the red PolyLine at the 
> seaside in a defined unit. My first idea was to use pythagoras in the 
> python console and I wrote this little script which I load with 
> execfile("script.py"):
>
> #!/usr/bin/env python
> from math import sqrt
> points = 
> dia.active_display().diagram.layers[0].objects[1].properties['poly_points']
> distance = 0
> size = len(points.value)
> for i in range(size):
>   a = points.value[i]
>   if i < size-1:
>     b = points.value[i+1]
>     distance += sqrt(pow(2,a.x-b.x) + pow(2,a.y-b.y))
Shouldn't the parameters to pow() be the other way around?

> print distance
>
> The problem is that the tuple points.value seems not to be ordered thus 
> points.value[42] is not always the same. 
What do you mean with "not always the same"? Looking just at the
Python bindings plug-ins/python/pydia-property.c(PyDia_get_PointArray)
you'll get the points in the same order as stored internally. And
that needs to be ordered to get the drawing right.

> So what can I do to mesasure 
> the length of this PolyLine correct? Except parsing the .dia xml by hand 
> :-)
After fixing the bug from above it should work ;-)

	Hans

-------- Hans "at" Breuer "dot" Org -----------
Tell me what you need, and I'll tell you how to
get along without it.                -- Dilbert