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SebKuzminsky
External polygon offsetting library: svgpathtools
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?
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.
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.
@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.
@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.
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.
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.
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.
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.
Just updating the status of the of the open issues in svgpathtools (based on the list by @SebKuzminsky):
- mathandy/svgpathtools#35
- mathandy/svgpathtools#37
- mathandy/svgpathtools#43