On 01/10/2013 04:52 PM, Bernhard Ströbl wrote:
Am 10.01.2013 16:12, schrieb Matthias Kuhn:
-- 8< snip --
"E.g. If you want to manually select features out of different subsets.
Let's say you have a layer with a lot of features and you're looking
for
a couple of cities (but not all of them) which have more than 100'000
inhabitants"
in extended selection enter: num_inhabitants > 100000
click: "new selection"
result (example): 150 datasets selected
"and some others which do not meet this criterion, but some
other criteria."
in extended selection enter: some_other_field = some_other_ctriteria
click: "add to selection"
result (example): 270 datasets selected (150 from before + 120
matching "some_other_criteria")
after that you can manually remove all datasets that you do not need
from the selection but I doubt this is a real use case, because how
would you decide which to keep and which to remove? Obviously because
some attributes match certain criteria, so here we go: e.g. user wants
to see only the cities with an airport
in extended selection enter: airport = false
click: "remove from selection"
result (example): 205 datasets selected (from the previosuly selected
65 do not have an airport and are therefore removed from the selection)
now have a look at the map and see where these cities are, in this
case manual removal seems imaginable, so lets remove 7 from the
selection; result: 198 datasets selected (205 - 7) in both table and
map!
now the user can do anything with this selection (update certain
fields, export to new dataset, use for a spatial query...)
I am of course totally aware that the 205 datasets can be achieved by
using only one query like "(num_inhabitants > 100000 OR
some_other_field = some_other_ctriteria) AND airport = true" but the
whole thing starts getting interesting when we imagine a spatial query
in the start e.g. "select all cities within 20 km from the sea" then
we could got to the attribute table enter "(num_inhabitants <= 100000
OR some_other_field != some_other_ctriteria) AND airport = false" and
click "remove from selection" to get a result containing all cities
with either more than 100000 inhabitants or some_other_ctriteria and
an airport and within 20 km of the sea
the "show only selected" checkbox should of course work as one would
expect it to i.e. whenever the selection changes, no matter if this
change originates from a user's click in the table or map or from
using one of the selection buttons the dataset shown contains _all_
currently selected datasets and _only_ them
I cannot imagine any use case that can not be tackled with what I
propose but I have a feeling that the filter/selection concept would
really confuse users
Ok, I think I got your idea.
Of course it is possible to generate a useful selection now already by
using an appropriate expression. This works as long as your requirements
are well defined (as in num_inhabitants > 100000 AND airport = true
etc.). Unfortunately that's not always the case as in this OSM data I've
had a look at recently, where the number of stories was supposed to be
in a field but sometimes something like "4-8", ">9" etc. was in there,
requiring special attention.
And there is the other use-case I mentioned in my last mail (and that's
probably the main reason): The attribute editor view (the one with the
list on the left and the attribute editor on the right) will greatly
benefit from the filter/selection paradigm.
In the example before (number of stories), you can apply a filter, to
only show the buildings not containing a clean number (i.e. requiring
inspection) and manually adjust the numbers to be in a consistent format
you can use. In this case you will need the selection to change (because
you change it, whenever you change the currently edited feature(s)) but
you don't want your filter to change before you finished inspecting all
the suspicious features.
bare with me I do not get your point here. Why would I change the
selection when I change a feature's value? We do not even have a
selection, do we? All we have is a filter. ...ahh wait a bit... the
filter is applied once and stays even if data are changed so they do
not match the filter anymore - but that is the current behaviour with
a selection, isn't it?
How if we had a selection and tick "show selected only" and switch to
the attribute view where we fix one dataset after another - would that
be any different from using the filter?
I really do like the dual view idea but do not understand why it is
linked to the filter.
The filter should always represent the current status of the data, even
when it changes.
The selection needs to be changed, because it defines which feature is
currently visible in the attribute editor (right side of the editor
view). And if you want to edit 5 different features one after the other,
you change the selection 5 times. Once you changed a certain feature, it
may disappear from the filter. The others stay visible. For the example
above this means: edit the data until all suspicious features
disappeared and you've got a clean dataset.
Matthias
I suppose we won't get around this (unless the dual view as a whole is
dumped) but I'm sure there is a possibility that will keep it as easy as
possible for every user.
Maybe a solution could be to detach the selection "advanced search" tool
from the attribute table (keeping it available with a button) as also
requested in http://hub.qgis.org/issues/6799. This tool could then also
implement your ideas such as "add to selection", "remove from selection"
and "intersect with selection".
+1 for #6790
Bernhard
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