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Re: [gpsd-users] Create an SVG skyview image from JSON data

From: Gary E. Miller
Subject: Re: [gpsd-users] Create an SVG skyview image from JSON data
Date: Sat, 6 Oct 2018 13:31:51 -0700

Yo Niccolo!

On Sat, 6 Oct 2018 17:20:31 +0200
Niccolo Rigacci <address@hidden> wrote:

> I made some changes to the script! This is a resumee.

Getting better.

> With your suggestion, now it runs also with Python3.


> Now the program can run in pipe with gpspipe, as documented into 
> the first lines of docstring.


> Now I get no complaint from pycodestyle nor pylint, EXCEPT for 
> the "line-too-long". I think that

Sadly your opinion is not in the majority.  God made punch cards 80
columns wide, and we stick with that.  Your code looks horrible to my
eye, as confirmed by pycodestyle and pylint.  And it is easy to fix.

Remember: no accounting for style, it just is.

But not a showstopper, when the rest is fixed, someone will fix that
for you.

> I sorted the satellite bar char by PRN.

Looks good.  Note that cgps and xgps sort by used, then by PRN.

> You said that "Signal Strength" is flat wrong, because it is 
> actually a Signal/Noise Ratio: yes, you are right! But I'm 
> preparing the SVG for non-expert people,

You need to get it right especially to non-experts!  Don't
teach them wrong stuff that they have to unlearn later.  Just
as you point out the 'ss' will haunt gpsd forever.

> Also you said that "horizontal precision" is wrong, it is DOP! 

Then we agree!  DOP is not precision.  DOP is dimensionless, 
a precision has a dimension/scale, like feet.

> Actually the displayed bars are not DOP ("less is better"), but 
> somewhat the inverse: a cutted-off value between a max and a min. 

Which is even worse, and even more misleading, but I did not
bring it up using the rule of "first failure".

Do it correctly, or don't do it.  The precision is in the
JSON, and it is exactly what non-experts need and expecct.

Nothing can be more clear to everyone than:
     estimated 2D error: 1 foot.

> About your question about the SVG viewer: it seems that in the 
> GNU/Linux world there are two main families: Imagemagick's 
> convert uses the library modules-Q16/coders/ (installed by 
> the libmagickcore-6.q16-3-extra Debian packages), other tools 
> uses the librsvg2 library (installed by the librsvg2-bin Debian 
> package). Programs that uses the latter are rsvg-convert, Gimp, 
> Geeqie, etc.

A bit oversimplied, but most of the common options.

> So I changed my script a bit, to circumvent this bug. Now I can 
> watch the produced SVG graphics with both families of tools.

Good, better.  I still have an issue on some hosts:

# display tmp.svg
Intrinsic has incorrect return type!
i8 addrspace(2)* ()* @llvm.amdgcn.dispatch.ptr
LLVM ERROR: Broken function found, compilation aborted!

Now you begin to see why svg never got very popular on the web...

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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