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<div class="moz-cite-prefix">On 2014-08-20 18:07, Peter Wendorff
wrote :<br>
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<blockquote cite="mid:53F4C7DD.8090904@uni-paderborn.de" type="cite">
<pre wrap="">Okay, let me get a bit more verbose.
I want to get Walmarts shown on the map in a different color.
Before there's a polygon with the following tags:
shop=supermarket
building=yes
operator=WalMart
addr:street=whatever
addr:housenumber:42
addr:city=YouLike
render=blue
Another polygon is tagged
shop=supermarket
building=yes
building:levels=2
operator=WalMart
addr:street=another street
addr:city=some city
Let's consider the usual rendering of the osm-carto (default mapnik)
stylesheet.
without considering the render tag both buildings are drawn as buildings
(dark outlined polygon filled in slightly lighter gray) and a shopping
cart icon on top.
Now let's consider the render-tag.
Variant 1: just use it. You get an entirely inconsistent look, as I
myself wasn't interested in all WalMarts, but probably only those in one
particular town, so I only added the render tag to some objects.
Let two others add arbitrary, but different render ideas to other
objects and the map get's unusable as there's nothing like a map key any
more: all visuals on the map get more or less meaningless.
Variant 2: Try to use the render tag, but in a consistent way.
In that case my stylesheet/renderer would have to figure out what is
meant by the render-tag. It may refer to supermarkets, to WalMarts, to
stuff in the whatever-street or in the city YouLike. Figuring out a rule
from that is incredibly hard and very error prone.
Your last sentence might be the misunderstanding:
"As soon as rendering is defined for an element, it is used instead and
RENDER is normally ignored".</pre>
</blockquote>
<br>
Yes, this sentence is misunderstood, and by many repliers
apparently.<br>
It means that once Mapnik uses a (defined) rendering you cannot
change it (RENDER is ignored).<br>
The main idea behind RENDER is not coloring objects, and I agree it
shouldn't, but showing them.<br>
And the renderer can do that with any single color they like.<br>
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<blockquote cite="mid:53F4C7DD.8090904@uni-paderborn.de" type="cite">
<pre wrap="">But even that is a tricky strategy. Let's stay at the WalMart-Example.
I want to have a special (!) rendering for WalMarts, so there is no
rendering defined for it before (as any rendering defined is a fallback
to a more generic case: supermarkets or even buildings).
It would therefore lead to cluttering map objects where it is not
necessary, or doesn't solve anything at all. Although it would break
down stylesheet innovation even more as you can render your very own
tags - as long as it isn't rendered on the map itself.
Put the effort to add rendering for missing objects. This is harder to
achieve, yes; but it is the straightforward way, not a hack around, with
major drawbacks and side effects.
regards
Peter
Am 20.08.2014 um 14:46 schrieb André Pirard:
</pre>
<blockquote type="cite">
<pre wrap="">On 2014-08-15 16:31, Peter Wendorff wrote :
</pre>
<blockquote type="cite">
<pre wrap="">not a good idea IMHO.
1) what is the feature this tag should refer to? Consider a polygon that
is tagged as a building (building=yes) and a shop (shop=supermarked) and
a Walmart (operator=WalMart), and the mapper added RENDER=blue. What is
it that should be rendered blue? This object? Any supermarket? any
Walmart?
</pre>
</blockquote>
<pre wrap="">I don't understand what you say very well. "added RENDER" to what?
As I say RENDER would typically apply to "an area", to one object, not
to "any".
That is, you have building=yes + render=blue and that building gets blue.
</pre>
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<pre wrap="">Any building? How should any rendering decide if the default
rendering should be used or the one defined by the tag you propose?
</pre>
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<pre wrap="">Did you read my sentence:
</pre>
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<blockquote type="cite">
<pre wrap="">As soon as rendering is defined for an element, it is used instead
and RENDER is normally ignored.
</pre>
</blockquote>
</blockquote>
<pre wrap="">?
a.s.o. ...
André.
</pre>
<blockquote type="cite">
<pre wrap="">2) I want to get Walmarts shown on the map in a different color, thus
all Walmarts I want to see in the map get
RENDER={mycolor-which-is-not-used-yet-in-the-zoomlevel-I'm-interested-in}.
Now the stylesheet maintainer uses that color for another object -
conflict, damn, fail.
3) I want to get Walmarts rendered pink on osm-carto, green on HOT,
orange on the cyclemap - what should go to the render-tag (even if the
styles would follow your proposal?
The only benefit I see in this proposal is just what you said: people
would stop tagging stuff just to get their map to display it the way
they want; but how do you ensure they don't tag stuff to be rendered
with the same style? How do you ensure the map stays usable?
regards
Peter
Am 15.08.2014 um 16:12 schrieb André Pirard:
</pre>
<blockquote type="cite">
<pre wrap="">Hi,
It's a well known fact that many people complain to tag in vain because
what they tag doesn't show on the map (e.g. mini-golf vs tennis pitch),
because they're told to open a rendering ticket which replies that only
official tags are supported, and because they open a vote for an
official tag and nobody signs.
As a result they are accused of "tagging for the renderer" instead of
'being forced to tag for the renderer".
The solution is simple however. A RENDER tag that, typically, would
assign a color to an area.
I'll let the rendering specialists define what else it can do.
⚠ ⚠ ⚠ RENDER only requests *by default* rendering.
As soon as rendering is defined for an element, it is used instead and
RENDER is normally ignored.
For a better map,
André.
</pre>
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