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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">I do that type of things with GMT’s mask module (-D option)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><a href="https://docs.generic-mapping-tools.org/latest/mask.html">https://docs.generic-mapping-tools.org/latest/mask.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> gdal-dev <gdal-dev-bounces@lists.osgeo.org>
<b>On Behalf Of </b>Paul Meems<br>
<b>Sent:</b> Friday, March 3, 2023 2:47 PM<br>
<b>To:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> Re: [gdal-dev] Convex hull with holes<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks Jukka for your reply.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I understand it is hard. <o:p></o:p></p>
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<p class="MsoNormal">In my case, I have a lot of data points making your edge case not a problem for me.<o:p></o:p></p>
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<p class="MsoNormal">The data points are collected driving over a field with 1 or more sensors.<o:p></o:p></p>
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<p class="MsoNormal">The result can be something like this:<br>
<img border="0" width="228" height="810" style="width:2.375in;height:8.4375in" id="Picture_x0020_1" src="cid:image001.png@01D94DE5.376CB160"><o:p></o:p></p>
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<p class="MsoNormal">The red dots are the data points and I manually created the black border and added a small buffer.<o:p></o:p></p>
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<p class="MsoNormal">The red dots are transformed into polygons using inverse distance and afterward, I need to 'blank' the data using the black border.<o:p></o:p></p>
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<p class="MsoNormal">I can automate all steps except for creating this field border.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I'm also struggling to get a proper name for my needs, making it harder to Google for a solution.<o:p></o:p></p>
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<p class="MsoNormal">'Convex hull' is not correct. What would be a more appropriate name?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Regards,<o:p></o:p></p>
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<p class="MsoNormal"><br>
Paul<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Op vr 3 mrt. 2023 om 14:13 schreef Rahkonen Jukka <<a href="mailto:jukka.rahkonen@maanmittauslaitos.fi">jukka.rahkonen@maanmittauslaitos.fi</a>>:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">Hi,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">So you have an uncategorized bunch of points and you wish to have an algorithm that recognizes outer and inner rings automatically? I fear that is not as easy
as it may appear. Have a look at the annexed image with two polygons having the same vertices. How could an algorithm know which interpretation is correct? In this simple case you could make a convex hull, delete the vertices which were consumed for the outer
ring, and create a new ring from the remaining points, but generally it will not work if there are two holes, for example.</span><span lang="FI"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><span lang="FI"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">If the points come from a GPX device, make the application to record indexes for both the points and the rings “ring1-point1, ring1-point2---ring2-point1,ring2-point2”
and construct the polygon ring by ring.</span><span lang="FI"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><span lang="FI"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">-Jukka Rahkonen-</span><span lang="FI"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US"> </span><span lang="FI"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="FI">Lähettäjä:</span></b><span lang="FI"> gdal-dev <<a href="mailto:gdal-dev-bounces@lists.osgeo.org" target="_blank">gdal-dev-bounces@lists.osgeo.org</a>>
<b>Puolesta </b>Paul Meems<br>
<b>Lähetetty:</b> perjantai 3. maaliskuuta 2023 14.52<br>
<b>Vastaanottaja:</b> <a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a><br>
<b>Aihe:</b> [gdal-dev] Convex hull with holes<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">How can I algorithmically create a parcel border that accounts for islands or holes within the parcel based on a list of coordinates? <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">While GDAL+GEOS has a Convex hull method, it only identifies the outer border. <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">Has GDAL+GEOS a method that I can use to detect inner holes as well, such as in a donut-shaped field?<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">The output can be json or shapefile, that doesn't matter.<br clear="all">
<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="FI">Thanks,<br>
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Paul Meems<o:p></o:p></span></p>
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