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<p>Hi Harrisou,</p>
<p>this looks a lot what I imagined (in the sense of some wicked
nested expression stuff i never would get to myself).</p>
<div class="moz-cite-prefix">Am 18.05.19 um 11:42 schrieb DelazJ:<br>
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cite="mid:CAECJsSrPPcBNbjfpGy81zsG9yEG90dA+W2DmErb6dNdW5tfP6w@mail.gmail.com">
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<div>Hi Bernd,</div>
<div>Hum.. interesting. Assuming you have two layers: <b>tracks
(id_track, date_track)</b> and <b>birds(id_bird, date_bird)</b>,
the idea is to get the id of the highest among the
date_track(s) lower than the date_bird for each bird. Am I
right?<br>
</div>
</div>
</blockquote>
<p>Well, erm, yes.</p>
<blockquote type="cite"
cite="mid:CAECJsSrPPcBNbjfpGy81zsG9yEG90dA+W2DmErb6dNdW5tfP6w@mail.gmail.com">
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<div> I gave it a shot and i think i have some working
expression. Here I display the matching track id in birds
labels<br>
</div>
<div><br>
attribute(<br>
get_feature ( 'tracks',</div>
<div> 'date_track',<br>
aggregate( layer:='tracks',<br>
aggregate:='max',<br>
expression:="date_track",<br>
filter:="date_track"<
attribute(@parent, 'date_bird')<br>
)<br>
),<br>
'id_track'</div>
<div>)<br>
</div>
<div><br>
</div>
<div>I used temporary layers with datetime field.</div>
<div>Now, without sample of dataset to actually see the date
formatting issue you were afraid of...</div>
</div>
</blockquote>
<p>The layers derive from ordinary gpx-files from the phone
generated with Locus. <br>
</p>
<p>I labeled the point and the track points with the date format in
the screenshot <a href="https://i.stack.imgur.com/MqPhK.jpg"
rel="noreferrer" target="_blank">https://i.stack.imgur.com/MqPhK.jpg</a>
QGIS sais the Type is <b>QDateTime</b> and the Typename is <b>DateTime</b>.
Indeed, date formats are a pain in the arse and its no fun
fumbling around with them most of the time.<br>
</p>
<p>Will give it a try tomorrow evening. Have to work all weekend in
the field, so already got as sunburn and tomorrow I will get
washed away.</p>
<p>Thanx a lot so far, I will report back!</p>
<p>Cheers,</p>
<p>Bernd<br>
</p>
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<div><br>
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<div>Hope that helps,</div>
<div>Harrissou<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Le ven. 17 mai 2019 à 20:34,
Bernd Vogelgesang <<a
href="mailto:bernd.vogelgesang@gmx.de"
moz-do-not-send="true">bernd.vogelgesang@gmx.de</a>> a
écrit :<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi
Mike,<br>
<br>
thank you for your hint, but the distance between the point
and the<br>
track is of no relevance for me.<br>
<br>
It seems that the screenshot I posted is a bit misleading<br>
(<a href="https://i.stack.imgur.com/MqPhK.jpg"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://i.stack.imgur.com/MqPhK.jpg</a>).
Seems I picked a point where the<br>
associated trackpoints are also the closest ones. But the
information we<br>
need is the time, where the observer was when taking the
observation.<br>
And this might also be on a more distant location.<br>
<br>
Furthermore, I do not intend to create a new layer. I'm just
looking for<br>
a way to highlight the track point(s) which compare best by
time with<br>
the selected observation point.<br>
<br>
So, still coulnd't find out how to query points in another
layer through<br>
an expression/ function, and in case I'll find out, how to
compare it<br>
with datetime values.<br>
<br>
Cheers,<br>
<br>
Bernd<br>
<br>
Am 16.05.19 um 13:28 schrieb Mike Flannigan:<br>
><br>
> Hi,<br>
><br>
> I'm thinking this is easier done outside of QGIS, but if
you<br>
> want to do in within QGIS this is one way:<br>
> <a
href="https://www.qgistutorials.com/en/docs/nearest_neighbor_analysis.html"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://www.qgistutorials.com/en/docs/nearest_neighbor_analysis.html</a><br>
><br>
><br>
> Mike<br>
><br>
><br>
> On 5/15/2019 1:17 PM, <a
href="mailto:qgis-user-request@lists.osgeo.org"
target="_blank" moz-do-not-send="true">qgis-user-request@lists.osgeo.org</a>
wrote:<br>
>> Hi folks,<br>
>> I'm sure there must be some "easy" solution, but
hours of searching<br>
>> provided no examples I could learn from to develop a
solution:<br>
>><br>
>> I have a point layer of bird observations and a
GPS-track recorded while<br>
>> observing the birds in an area.<br>
>> For the interpretation of the findings it would be
good to easily find<br>
>> out, from which position the recorded observation was
taken.<br>
>><br>
>> My idea was to compare the timestamp of the bird
point with the<br>
>> timestamps of the track points, but I run into huge
obstacles right at<br>
>> start:<br>
>> I know that I "could" query across layers by the
expression aggregate().<br>
>> Unfortunately, the docs on that is so sparse, that I
have not the<br>
>> slightest idea how to even start with that<br>
>> (<a
href="https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/expression.html?highlight=expression#aggregates-functions"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/expression.html?highlight=expression#aggregates-functions</a>)<br>
>><br>
>><br>
>> Ok, in case I could find out how to properly use
aggregate, how do I<br>
>> best compare those time stamps?<br>
>> The layers derive from gpx-files and QGIS identifies
the time tag as<br>
>> QDateTime.<br>
>><br>
>> As it is not very likely that a bird observation was
recorded at the<br>
>> exact same time as a track point was generated, there
is no way to<br>
>> actually compare the values, cause the bird time
value will always lie<br>
>> in between two track point values.<br>
>> What kind of query can be used to identify those two
trackpoints ?<br>
>><br>
>> In short: How can I identify/highligt/mark track
points that have a<br>
>> timestamp close the selected point in another layer?<br>
>><br>
>> I already created a question on this on gis
stackexchange with a<br>
>> screenshot,but no reactions so far.<br>
>><br>
>><br>
>> Thankful for any hint<br>
>> Bernd<br>
><br>
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