<div dir="ltr">HELP unsubscribe please</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Oct 6, 2024 at 3:00 PM <<a href="mailto:gdal-dev-request@lists.osgeo.org">gdal-dev-request@lists.osgeo.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Send gdal-dev mailing list submissions to<br>
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Today's Topics:<br>
<br>
1. What are vector field width and precision good for? (Sean Gillies)<br>
2. Re: What are vector field width and precision good for?<br>
(Even Rouault)<br>
3. Re: What are vector field width and precision good for?<br>
(Sean Gillies)<br>
4. Re: What are vector field width and precision good for?<br>
(Even Rouault)<br>
<br>
<br>
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Message: 1<br>
Date: Sat, 5 Oct 2024 16:38:14 -0600<br>
From: Sean Gillies <<a href="mailto:sean.gillies@gmail.com" target="_blank">sean.gillies@gmail.com</a>><br>
To: gdal dev <<a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a>><br>
Subject: [gdal-dev] What are vector field width and precision good<br>
for?<br>
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<br>
Hi all,<br>
<br>
What are vector field width and precision good for in 2024? These concepts<br>
were inherited from MS Access via Shapefile, I believe. I've been wondering<br>
if I can stop supporting them in my Fiona project without breaking<br>
workflows badly. Numpy data types don't have width and precision. Neither<br>
do, for example, Parquet and Arrow.<br>
<br>
Anybody using these for anything crucial?<br>
<br>
-- <br>
Sean Gillies<br>
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Message: 2<br>
Date: Sun, 6 Oct 2024 00:48:09 +0200<br>
From: Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">even.rouault@spatialys.com</a>><br>
To: Sean Gillies <<a href="mailto:sean.gillies@gmail.com" target="_blank">sean.gillies@gmail.com</a>>, gdal dev<br>
<<a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a>><br>
Subject: Re: [gdal-dev] What are vector field width and precision good<br>
for?<br>
Message-ID: <<a href="mailto:bcdc66c7-6002-41c3-96bb-0498e2c738ba@spatialys.com" target="_blank">bcdc66c7-6002-41c3-96bb-0498e2c738ba@spatialys.com</a>><br>
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<br>
Sean,<br>
<br>
> What are vector field width and precision good for in 2024? These <br>
> concepts were inherited from MS Access via Shapefile, I believe. I've <br>
> been wondering if I can stop supporting them in my Fiona project <br>
> without breaking workflows badly. Numpy data types don't have width <br>
> and precision. Neither do, for example, Parquet and Arrow.<br>
><br>
> Anybody using these for anything crucial?<br>
<br>
If Fiona had only a read side you could likely ignore them.? But writing <br>
all those formats (shapefile, mapinfo, etc.) require setting those <br>
properties. If you don't specify them, the OGR drivers will use some <br>
defaults, that might not always be appropriate.<br>
<br>
Even<br>
<br>
-- <br>
<br>
<a href="http://www.spatialys.com" rel="noreferrer" target="_blank">http://www.spatialys.com</a><br>
My software is free, but my time generally not.<br>
<br>
<br>
<br>
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<br>
Message: 3<br>
Date: Sat, 5 Oct 2024 17:32:18 -0600<br>
From: Sean Gillies <<a href="mailto:sean.gillies@gmail.com" target="_blank">sean.gillies@gmail.com</a>><br>
To: gdal dev <<a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a>><br>
Subject: Re: [gdal-dev] What are vector field width and precision good<br>
for?<br>
Message-ID:<br>
<<a href="mailto:CAOodmJocW4yVShE_yacvUMFyLfo04p0oToB%2BZzoevt1AsZJr0w@mail.gmail.com" target="_blank">CAOodmJocW4yVShE_yacvUMFyLfo04p0oToB+Zzoevt1AsZJr0w@mail.gmail.com</a>><br>
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<br>
Even,<br>
<br>
Would the defaults result in overly large attribute files? By a small<br>
amount or an excessive amount? Or would the defaults result in truncation<br>
of values?<br>
<br>
On Sat, Oct 5, 2024 at 4:48?PM Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">even.rouault@spatialys.com</a>><br>
wrote:<br>
<br>
> Sean,<br>
><br>
> > What are vector field width and precision good for in 2024? These<br>
> > concepts were inherited from MS Access via Shapefile, I believe. I've<br>
> > been wondering if I can stop supporting them in my Fiona project<br>
> > without breaking workflows badly. Numpy data types don't have width<br>
> > and precision. Neither do, for example, Parquet and Arrow.<br>
> ><br>
> > Anybody using these for anything crucial?<br>
><br>
> If Fiona had only a read side you could likely ignore them. But writing<br>
> all those formats (shapefile, mapinfo, etc.) require setting those<br>
> properties. If you don't specify them, the OGR drivers will use some<br>
> defaults, that might not always be appropriate.<br>
><br>
> Even<br>
><br>
<br>
<br>
-- <br>
Sean Gillies<br>
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Message: 4<br>
Date: Sun, 6 Oct 2024 11:19:35 +0200<br>
From: Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">even.rouault@spatialys.com</a>><br>
To: Sean Gillies <<a href="mailto:sean.gillies@gmail.com" target="_blank">sean.gillies@gmail.com</a>>, gdal dev<br>
<<a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a>><br>
Subject: Re: [gdal-dev] What are vector field width and precision good<br>
for?<br>
Message-ID: <<a href="mailto:a4668df8-5d70-49fe-be5a-f57ee09980bf@spatialys.com" target="_blank">a4668df8-5d70-49fe-be5a-f57ee09980bf@spatialys.com</a>><br>
Content-Type: text/plain; charset=UTF-8; format=flowed<br>
<br>
Sean,<br>
><br>
> Would the defaults result in overly large attribute files? By a small <br>
> amount or an excessive amount? Or would the defaults result in <br>
> truncation of values?<br>
<br>
For shapefile the default is width=24,precision=15,so this means 24 <br>
bytes for every floating point number. In theory a number couldn't have <br>
a magnitude larger than 10^(24-15-1), but the shapefile driver will <br>
remove decimal figures if that's needed to preserve the integer part. <br>
But if a number is larger than 10^24, its last digits will just be <br>
truncated with a warning (there's no good solution here. I kind of <br>
remember of past discussions if we shouldn't fallback to scientific <br>
notation, but we didn't implement that). In that situation, the user <br>
would have to increase the width (one can question the appropriateness <br>
of using Shapefile .dbf for numbers of very large magnitude). So <br>
basically the default should be fine (as far as preserving information <br>
is concerned) for most common ranges of floating point numbers, but will <br>
misbehave for very large ones. Obviously for people storing small <br>
numbers with few decimals, 24 might be felt as excessive.<br>
<br>
For MapInfo I was actually partially incorrect. It has indeed a mode of <br>
fixed precision, but if you don't specify the width, it uses IEEE754 <br>
double precision for .tab, et a non-fixed width text representation for <br>
.mif.<br>
<br>
Shapefiles are (probably) the only format OGR handles on the writing <br>
side that require, explicit or implict, width.precision (PostGIS or <br>
other databases are similar to MapInfo and support both fixed <br>
width/precision and floating-point)<br>
<br>
Even<br>
<br>
-- <br>
<a href="http://www.spatialys.com" rel="noreferrer" target="_blank">http://www.spatialys.com</a><br>
My software is free, but my time generally not.<br>
<br>
<br>
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