Hi,
You should create your own algorithm. For instance, in non-optimal and not well written pseudo c++:

void mergeLineStrings(std::vector<line_string>& in, std::vector<line_string>& out, double threshlod) {
  // Process first item of "in"
  auto toProcess = in.front(); // This copy should be avoided
  in.erase(in.begin()); // So remove it from container
  for (auto outIt=out.begin(); outIt!=out.end(); outIt++) {
    // see if first point of toProcess and first point of outIt are close enough to merge
    if (distance(toProcess.begin(), outIt->begin()) < threshold) {
      // insert points from toProcess at the beginning of outIt
      ...
      return;
    }
    // see if first point of toProcess and last point of outIt are close enough to merge
    ...
    // see if last point of toProcess and first point of outIt are close enough to merge
    ...
    // see if last point of toProcess and last point of outIt are close enough to merge
    ...
  }
  // Found no out line_string to merge with, add toProcess in out line_strings
  out.push_back(toProcess);
}

// Processing would be
std::vector<line_string> in = {{....}};
std::vector<line_string> out;
while (!in.empty()) {
  mergeLineStrings(in,out, threshold);
}

Hope that helps.
Cheers
Matthieu Beghin

On Fri, Sep 20, 2019 at 8:59 AM Ahmet Temiz via Geometry <geometry@lists.boost.org> wrote:
Hi,

Thank you all.
I need to merge lines that are in certain distances. Lines represent the roads. The result looks like some dashed lines. if  they are not  merged. 

Previously I tried geos lib's linemerger function. The result was not satisfactory. 

I looked at boost's append. It is for appending point to a line. 

What am I looking for appending a line to another line if it is in certain distance ( may be a threshold value).

I am going to look at  bg::distance().

Do you have any other recommendations ?

regards



On Thu, Sep 19, 2019 at 7:12 PM Adam Wulkiewicz via Geometry <geometry@lists.boost.org> wrote:
W dniu 19.09.2019 o 15:09, Mateusz Loskot via Geometry pisze:
> On Thu, 19 Sep 2019 at 13:01, Ahmet Temiz via Geometry
> <geometry@lists.boost.org> wrote:
>> I want to merge some partial lines (roads) to a continuous single line based on certain proximity.
>>
>> Can you guide me to use relevant function?
> Have you browsed through the API reference for potential candidates?
>
> For example, this one
> https://www.boost.org/libs/geometry/doc/html/geometry/reference/algorithms/append.html
> and this may be helpful
> https://github.com/boostorg/geometry/blob/develop/example/02_linestring_example.cpp

Well, I don't know if that's what is needed here. AFAIU there is some
reference line (linestring or segment?) and the problem is that some
other lines that are closer than some distance threshold should be
filtered out from a set of these other lines. Is that correct? If it is
then you probably only need bg::distance() or bg::comparable_distance().
But these functions will return the minimum distance between two
linestrings so if you define proximity differently then you'll need
something else.

So if the above does not apply please expand the explanation of the
problem defining what does "partial lines", "merge", "continuous single
line" and "proximity" mean exactly.

Adam

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