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SebKuzminsky / pycam

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External polygon offsetting library: svgpathtools #113

Open sumpfralle opened 6 years ago

sumpfralle commented 6 years ago

Maybe svgpathtools could be suitable external library for calculating polygon offsets (proposed by SebKuzminsky):

https://github.com/mathandy/svgpathtools

I don't yet know if svgpathtools is the external libaray we should use. If it is, i think we have two options:

Package svgpathtools as a debian package and have pycam Depend on it, or Include svgpathtools as a submodule in the pycam git repo and include it in the pycam package.

Is it suitable for polygon offsetting? Should we use it?

SebKuzminsky commented 6 years ago

svgpathtools does not currently include polygon offsetting, though it does include primitives from which polygon offsetting can be implemented. I've sketched out a polygon offsetting function based on svgpathtools, but bugs in svgpathtools prevent it from working robustly. Details in #114.

ebo commented 6 years ago

On Feb 16 2018 10:05 AM, Sebastian Kuzminsky wrote:

svgpathtools does not currently include polygon offsetting, though it does include primitives from which polygon offsetting can be implemented. I've sketched out a polygon offsetting function based on svgpathtools, but bugs in svgpathtools prevent it from working robustly. Details in #114.

by polygon offsetting I assume you mean the 2D equivalent of offset surfaces or parallel curve https://en.wikipedia.org/wiki/Parallel_curve. Am I correct?

As a note, I worked with the Spatial Ontology Community of Practice (SOCoP) and GeoVoCamp a couple of years ago working on formal definitions of map contours. We had talked about extending this to surfaces, and abstract surfaces over time, but I cannot remember where that got to. If interested I will look for the paper that Torsten wrote from that ontological formalism. The proofs will provide you with some fodder for unit tests and regression tests.

SebKuzminsky commented 6 years ago

@ebo Yes exactly, the offset polygon consists of the parallel curve (with a specific distance) of the original polygon. It's used for tool radius compensation, and it can also be used to compute a pocketing toolpath.

ebo commented 6 years ago

@Sebastian, yep. I have used it before. Let me know off list and I will see what I can get for you for theoretical references that might be very helpful (like Ferin's work on curves and surfaces)

On Feb 16 2018 12:07 PM, Sebastian Kuzminsky wrote:

@ebo Yes exactly, the offset polygon consists of the parallel curve (with a specific distance) of the original polygon. It's used for tool radius compensation, and it can also be used to compute a pocketing toolpath.

SebKuzminsky commented 6 years ago

One thing I like about svgpathtools is that it supports all the path segment types of SVG: lines, elliptic arcs, and quadratic and cubic bezier splines. Arcs especially are common in part designs, and supporting them directly, without using linear-spline approximations, is a good thing.

ebo commented 6 years ago

Nice! What are the bugs that are keeping it from being used? From a comment before I thought that svgpathtools was sufficiently buggy that you could not use it.

On Feb 16 2018 12:51 PM, Sebastian Kuzminsky wrote:

One thing I like about svgpathtools is that it supports all the path segment types of SVG: lines, elliptic arcs, and quadratic and cubic bezier splines. Arcs especially are common in part designs, and supporting them without using linear-spline approximations is a good thing.

SebKuzminsky commented 6 years ago

The bugs i've found in svgpathtools (so far...) are:

I fixed some of those issues and offered PRs, but they have not been accepted yet:

The last bug, mathandy/svgpathtools#43, is the only thing I know of preventing the svgpathtools-based polygon offsetting code I wrote from working reliably.

ebo commented 6 years ago

I'm swamped enough I will unfortunately not be able to look into this.

On Feb 16 2018 1:09 PM, Sebastian Kuzminsky wrote:

The bugs i've found in svgpathtools (so far...) are:

  • mathandy/svgpathtools#35
  • mathandy/svgpathtools#37
  • mathandy/svgpathtools#41
  • mathandy/svgpathtools#43

I fixed some of those issues and offered PRs, but they have not been accepted yet:

  • mathandy/svgpathtools#40
  • mathandy/svgpathtools#42

The last bug, mathandy/svgpathtools#43, is the only thing I know of preventing the svgpathtools-based polygon offsetting code I wrote from working reliably.

sumpfralle commented 6 years ago

Just updating the status of the of the open issues in svgpathtools (based on the list by @SebKuzminsky):