[gdal-dev] gdal-dev Digest, Vol 245, Issue 7
Vincent Autieri II
vautieri at geoweb3d.com
Mon Oct 7 07:50:17 PDT 2024
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On Sun, Oct 6, 2024 at 3:00 PM <gdal-dev-request at lists.osgeo.org> wrote:
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> Today's Topics:
>
> 1. What are vector field width and precision good for? (Sean Gillies)
> 2. Re: What are vector field width and precision good for?
> (Even Rouault)
> 3. Re: What are vector field width and precision good for?
> (Sean Gillies)
> 4. Re: What are vector field width and precision good for?
> (Even Rouault)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 5 Oct 2024 16:38:14 -0600
> From: Sean Gillies <sean.gillies at gmail.com>
> To: gdal dev <gdal-dev at lists.osgeo.org>
> Subject: [gdal-dev] What are vector field width and precision good
> for?
> Message-ID:
> <CAOodmJo26kYqC=M_3PHNJwzK=
> 3Q0UdjLDZKxJg0JwwkNW5774A at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi all,
>
> What are vector field width and precision good for in 2024? These concepts
> were inherited from MS Access via Shapefile, I believe. I've been wondering
> if I can stop supporting them in my Fiona project without breaking
> workflows badly. Numpy data types don't have width and precision. Neither
> do, for example, Parquet and Arrow.
>
> Anybody using these for anything crucial?
>
> --
> Sean Gillies
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> ------------------------------
>
> Message: 2
> Date: Sun, 6 Oct 2024 00:48:09 +0200
> From: Even Rouault <even.rouault at spatialys.com>
> To: Sean Gillies <sean.gillies at gmail.com>, gdal dev
> <gdal-dev at lists.osgeo.org>
> Subject: Re: [gdal-dev] What are vector field width and precision good
> for?
> Message-ID: <bcdc66c7-6002-41c3-96bb-0498e2c738ba at spatialys.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> Sean,
>
> > What are vector field width and precision good for in 2024? These
> > concepts were inherited from MS Access via Shapefile, I believe. I've
> > been wondering if I can stop supporting them in my Fiona project
> > without breaking workflows badly. Numpy data types don't have width
> > and precision. Neither do, for example, Parquet and Arrow.
> >
> > Anybody using these for anything crucial?
>
> If Fiona had only a read side you could likely ignore them.? But writing
> all those formats (shapefile, mapinfo, etc.) require setting those
> properties. If you don't specify them, the OGR drivers will use some
> defaults, that might not always be appropriate.
>
> Even
>
> --
>
> http://www.spatialys.com
> My software is free, but my time generally not.
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sat, 5 Oct 2024 17:32:18 -0600
> From: Sean Gillies <sean.gillies at gmail.com>
> To: gdal dev <gdal-dev at lists.osgeo.org>
> Subject: Re: [gdal-dev] What are vector field width and precision good
> for?
> Message-ID:
> <
> CAOodmJocW4yVShE_yacvUMFyLfo04p0oToB+Zzoevt1AsZJr0w at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Even,
>
> Would the defaults result in overly large attribute files? By a small
> amount or an excessive amount? Or would the defaults result in truncation
> of values?
>
> On Sat, Oct 5, 2024 at 4:48?PM Even Rouault <even.rouault at spatialys.com>
> wrote:
>
> > Sean,
> >
> > > What are vector field width and precision good for in 2024? These
> > > concepts were inherited from MS Access via Shapefile, I believe. I've
> > > been wondering if I can stop supporting them in my Fiona project
> > > without breaking workflows badly. Numpy data types don't have width
> > > and precision. Neither do, for example, Parquet and Arrow.
> > >
> > > Anybody using these for anything crucial?
> >
> > If Fiona had only a read side you could likely ignore them. But writing
> > all those formats (shapefile, mapinfo, etc.) require setting those
> > properties. If you don't specify them, the OGR drivers will use some
> > defaults, that might not always be appropriate.
> >
> > Even
> >
>
>
> --
> Sean Gillies
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> ------------------------------
>
> Message: 4
> Date: Sun, 6 Oct 2024 11:19:35 +0200
> From: Even Rouault <even.rouault at spatialys.com>
> To: Sean Gillies <sean.gillies at gmail.com>, gdal dev
> <gdal-dev at lists.osgeo.org>
> Subject: Re: [gdal-dev] What are vector field width and precision good
> for?
> Message-ID: <a4668df8-5d70-49fe-be5a-f57ee09980bf at spatialys.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> Sean,
> >
> > Would the defaults result in overly large attribute files? By a small
> > amount or an excessive amount? Or would the defaults result in
> > truncation of values?
>
> For shapefile the default is width=24,precision=15,so this means 24
> bytes for every floating point number. In theory a number couldn't have
> a magnitude larger than 10^(24-15-1), but the shapefile driver will
> remove decimal figures if that's needed to preserve the integer part.
> But if a number is larger than 10^24, its last digits will just be
> truncated with a warning (there's no good solution here. I kind of
> remember of past discussions if we shouldn't fallback to scientific
> notation, but we didn't implement that). In that situation, the user
> would have to increase the width (one can question the appropriateness
> of using Shapefile .dbf for numbers of very large magnitude). So
> basically the default should be fine (as far as preserving information
> is concerned) for most common ranges of floating point numbers, but will
> misbehave for very large ones. Obviously for people storing small
> numbers with few decimals, 24 might be felt as excessive.
>
> For MapInfo I was actually partially incorrect. It has indeed a mode of
> fixed precision, but if you don't specify the width, it uses IEEE754
> double precision for .tab, et a non-fixed width text representation for
> .mif.
>
> Shapefiles are (probably) the only format OGR handles on the writing
> side that require, explicit or implict, width.precision (PostGIS or
> other databases are similar to MapInfo and support both fixed
> width/precision and floating-point)
>
> Even
>
> --
> http://www.spatialys.com
> My software is free, but my time generally not.
>
>
>
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> End of gdal-dev Digest, Vol 245, Issue 7
> ****************************************
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--
*Vincent Autieri*
Vice President Co-Founder, Geoweb3d Inc.
607-323-1114 <607-731-3904> | vautieri at geoweb3d.com |
http://www.geoweb3d.com
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