<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">2014-11-08 11:53 GMT+01:00 Barend Gehrels [via Boost] <span dir="ltr"><<a href="/user/SendEmail.jtp?type=node&node=4669040&i=0" target="_top" rel="nofollow" link="external">[hidden email]</a>></span>:<br><blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>Gu Grzegorz,<br>
<br>
gchlebus wrote On 8-11-2014 2:33:<br>
</div>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" type="cite">
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<div class="gmail_extra"><br>
<div class="gmail_quote">2014-11-07 19:30 GMT+01:00 Barend
Gehrels [via Boost] <span dir="ltr"><<a href="http://user/SendEmail.jtp?type=node&node=4668825&i=0" rel="nofollow" link="external" target="_blank">[hidden
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<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" class="gmail_quote">
<div>Hi Grzegorz,<br>
<br>
gchlebus wrote On 6-11-2014 19:08:<br>
</div>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" type="cite">
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<div class="gmail_quote">2014-11-04 17:23 GMT+01:00
Barend Gehrels [via Boost] <span dir="ltr"><<a href="http://user/SendEmail.jtp?type=node&node=4668774&i=0" rel="nofollow" link="external" target="_blank">[hidden
email]</a>></span>:
<div>
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<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" class="gmail_quote">
<div>Hi Grzegorz,<br>
<br>
<br>
</div>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" type="cite">
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<div class="gmail_quote">2014-10-29
23:18 GMT+01:00 Barend Gehrels [via
Boost] <span dir="ltr"><<a href="http://user/SendEmail.jtp?type=node&node=4668617&i=0" rel="nofollow" link="external" target="_blank">[hidden email]</a>></span>:<span><br>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" class="gmail_quote"> <br>
<span><br>
gchlebus wrote On 24-10-2014
16:44: </span>
<div>
<div><span><br>
> Hi, <br>
> <br>
> I am wondering whether
it would be possible to
achieve anisotropic
buffering <br>
> (distances in neg x,
pos x, neg y, pos y can have
different values) of a <br>
> polygon using the
buffer function with
custom-implemented distance
strategy. <br>
> What I want to achieve
is presented on the figure
2-b in the following <br>
> paper: <br>
> <a href="http://itcnt05.itc.nl/agile_old/Conference/mallorca2002/proceedings/posters/p_molina.pdf" rel="nofollow" link="external" target="_blank">http://itcnt05.itc.nl/agile_old/Conference/mallorca2002/proceedings/posters/p_molina.pdf</a><br>
> <br>
</span>> I would be
grateful to hear from you
whether it is doable, and if
positive, <br>
> how one could implement
such a custom distance
strategy. </div>
</div>
The current distance strategy has
(currently) no means to get the
angle, <br>
or a vector of the new point to be
buffered. We can consider adding
that. <br>
<br>
However, by writing custom
strategies for join, side, point
(for <br>
point-buffers) and possibly end
(for line-buffers) you should be
able to <br>
create this, because these have
this information. <br>
<br>
Attached a program doing similar
things with polygons and points (I
vary <br>
the distance based on angle - you
will have to do something with
your <br>
anistropic model). <br>
<br>
The output is also attached. <br>
<br>
The program defines three custom
strategies, all based on the same
<br>
mechanism, to create interesting
output. <br>
I did not do the end-strategy but
that would look similar, you can
look <br>
at the provided end-strategy
(round) and apply the same
function. <br>
<span></span></blockquote>
</span></div>
</div>
</blockquote>
<br>
<br>
gchlebus wrote On 31-10-2014 18:13:<span><br>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em" type="cite">
<div dir="ltr">I really appreciate your
example code, it helped me a lot.
Attached you can find my source code.
<div>In my implementation of the
anisotropic buffering I didn't know
how to make use of the distance
strategy, as it was possible to make
it work using only side and join
strategies.</div>
<div>I encountered strange behavior
when changing number of points
describing a full circle. Using 360
points produced a good output,
whereas 90 points caused only the
second polygon to be buffered (see
attached figures). I would be
thankful if you could help me to
resolve this issue as well as for
any remarks to my code.</div>
<div><br>
</div>
</div>
</blockquote>
<br>
</span> I could reproduce this. Basically
the join-strategy should always include
points perp1 and perp2 (these are the two
points perpendicular to the two sides which
the join-strategy joints). Either they are
re-calculated, or they can be just added to
begin and end. So I did the last option, and
that piece of code now looks like:<br>
<br>
double const angle_increment = 2.0 *
M_PI / double(point_count);<br>
double alpha = angle1 -
angle_increment;<br>
<b> range_out.push_back(perp1);</b><b>
// added<br>
</b> for (int i = 0; alpha >= angle2
&& i < point_count; i++, alpha -=
angle_increment)<br>
{<br>
pdd v = getPointOnEllipse(alpha);<br>
Point p;<br>
bg::set<0>(p,
bg::get<0>(vertex) + v.first);<br>
bg::set<1>(p,
bg::get<1>(vertex) + v.second);<br>
range_out.push_back(p);<br>
}<br>
<b> range_out.push_back(perp2);</b><b>
// added</b><br>
<br>
My sample code of course also suffered from
that, so I added it there too if I use it in
the future.<br>
<br>
I tested your algorithm with various points
and distances and it now seems always OK.<br>
<br>
You ask for remarks on your code: it looks
good ;-) one thing, many terms are
recalculated such as pow(xPos*tan(alpha),
2)); or just tan(alpha), I usually store
these into variables, to avoid expensive
recalculations of the same terms, though
maybe they are optimized by the compiler.<br>
<br>
Regards, Barend<br>
<br>
<br>
P.S. this list discourages top-postings<span><br>
<br>
</span></blockquote>
<div><br>
</div>
<div>Hallo Barend,</div>
<div><br>
</div>
<div>I corrected the join strategy, but still
the buffering doesn't work in all cases as
expected. When using xPos = 1, and other
values equal 0, the buffered polygon
contains a hole (see xPos1.svg), whereas
setting xPos to 2 produces a correct result
(xPos2.svg). Do you know how to fix it? I
attached also main.cpp, as I changed the
code a bit and it contains the polygon for
which causes the strange behavior.</div>
<div><br>
</div>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
<br>
That is most probably caused by an error in some of your
calculations:<br>
<br>
The line y = sqrt(yPos2 * (1 - pow(x, 2) / xNeg2));<br>
causes a NAN for this input:<br>
<br>
alpha about PI<br>
then xNeg2 = 0.010000000000000002<br>
and x = -0.10000000000000002<br>
and yPos2 = 0.010000000000000002<br>
<br>
This adds a weird line containing NAN to the join, causing
the buffer process fail.<br>
I got this using these parameters:<br>
double xPos = 1.0, xNeg = 0.1, yPos = 0.1, yNeg = 0.1;<br>
<br>
and not the parameters you have (that was fine for me).<br>
<br>
I think you should make the calculations full-proof
first...<br>
<br>
For example add a line in the join-strategy:<br>
std::cout << i << " "<< angle1
<< " " << angle2 << " " << v.first
<< " " << v.second << std::endl;<br>
<br>
<br>
Regards, Barend<span><br>
<br>
</span></blockquote>
<div><br>
</div>
<div>Thanks, I'll try to improve my calculations. </div>
<div>By the way, I was playing with different strategies
combinations and I found out that when using only boost
buffer strategies:</div>
<div>
<div> </div>
<div> double points_per_circle = 36;</div>
<div> double distance = 130;</div>
<div>
bg::strategy::buffer::distance_symmetric<double>
distance_strategy(distance); </div>
<div><span style="white-space:pre-wrap"> </span>bg::strategy::buffer::end_flat
end_strategy; </div>
<div><span style="white-space:pre-wrap"> </span>bg::strategy::buffer::point_circle
point_strat(points_per_circle);</div>
<div><span style="white-space:pre-wrap"> </span>bg::strategy::buffer::side_straight
sideStrat;</div>
<div><span style="white-space:pre-wrap"> </span>bg::strategy::buffer::join_round
joinStrat(points_per_circle);</div>
</div>
<div><br>
</div>
<div>the buffer function can still fail (produce no output)
when the distance is higher than 128 (e.g, 128, 130, 150,
300, 400). But this happens up to a certain value, where
the buffer function starts producing a correct output
(e.g., distances 900, 1000). </div>
<div><br>
</div>
</div></div></div>
</div>
</div>
</blockquote>
<br>
Hmm, I see (starting at different values, but I can reproduce).<br>
<br>
I created a ticket, will be looked at. Thanks for reporting.<br>
<a href="https://svn.boost.org/trac/boost/ticket/10770" rel="nofollow" link="external" target="_blank">https://svn.boost.org/trac/boost/ticket/10770</a><span class=""><br>
<br>
Barend<br>
<br></span></blockquote><div><br></div><div>Hi Barend,</div><div><br></div><div>I'm glad that I could help. </div><div>Anyway, I fixed the bug with NAN, but still when using (e.g. xNeg = 1, other 0) the buffer produces no output. I am really wondering, how it could work on your machine.</div><div>I printed the values used by join and side strategies and they seem to be fine (no NANs or other strange values) - see attached log.txt and updated main.cpp used to produce the log file.</div><div><br></div><div>I've compiled my code using msvc 12.0 and gcc 4.8.</div><div><br></div><div><br></div><div>Best,</div><div>Grzegorz </div></div></div></div>
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