<div dir="ltr">Rendering will always be an imperfect representation of the real world.<div>I still feel that there is an inconsistency with the way these two circumstances are handled, but understand that this is one of the non-open parts of Open Street Map.</div><div>I'm done trying to swim upstream on this.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Mar 2, 2018 at 7:17 AM, Volker Schmidt <span dir="ltr"><<a href="mailto:voschix@gmail.com" target="_blank">voschix@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div>The layers tag in OSM is only to enable the renderer to display/draw crossing OSM elements correctly. The element with the higher layer value is drown over the ones with lower layer values.<br><br></div>In the case of the ford the waterway and the highway are on the same layer and share a node, which represents the ford (assuming that highway and waterway are line objects. If the waterway and/or the highway are drawn as polygons, then the ford becomes a line or a polygon.)<br><br></div>In case of a culvert the objects are not on the same layer. The highway is above the waterway (which may be intermittent or a wadi). Hence a common node is not correct. You could argue that the culvert becomes a node on the lower way, that is not connected with the highway above. It would have to be drawn exactly on the crossing point, without being part of the highway above. A non-zero length culvert is most likely easier to draw, and also closer to reality.<br></div>Again, when the waterway is drawn as a Polygon, the culvert becomes a polygon.<br></div><div class="gmail_extra"><br><div class="gmail_quote">On 2 March 2018 at 15:41, Vao Matua <span dir="ltr"><<a href="mailto:vaomatua@gmail.com" target="_blank">vaomatua@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Thank you Ralph, I understand your perspective, but have to disagree a bit (I'm not looking for a battle, however).<div><br></div><div>A ford is a stack of layers that are directly adjacent vertically, with the road slightly below the stream/river. In the dry season a ford is only a road and only becomes a ford when a watercourse flows over the top of the road.</div><div><br></div><div><div>A culvert is a part of of road construction, a culvert would not exist without the road, but the culvert is utilized by the stream. Personally I have physically installed culverts in road profiles where there is no watercourse. If I try to add a culvert in JOSM without an additional tag I get a validation warning.</div></div><div><br></div><div>Wouldn't a road/stream crossing without a culvert or bridge be called a dam?</div><div><br></div><div>Isn't a culvert similar in rendering to an embankment? An embankment is a tag applied to a road or railroad, but it is a level beneath the road or railroad. A culvert happens to be perpendicular or so to the road rather than adjacent to it.</div><div><br></div><div>Part of this discussion also is a matter of scale. At some rendering of a map even a place like Paris would be displayed as a node. In the same way a culvert displayed as a node would be appropriate at certain zoom levels.</div><div><br></div><div>I think an easy solution is to make the rendering rule for culverts be a layer below the road and allowed to be a node.</div><div><br></div><div>I think this is an interesting discussion and is helping me understand different points of view, thanks.</div><div><br></div><div>Emmor</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Mar 2, 2018 at 12:39 AM, Ralph Aytoun <span dir="ltr"><<a href="mailto:ralph.aytoun@ntlworld.com" target="_blank">ralph.aytoun@ntlworld.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div link="blue" vlink="#954F72" lang="EN-US"><div class="m_3997525186325245298m_-7114438077408154712m_2986510220553085687WordSection1"><p class="MsoNormal"><span lang="EN-GB">The real easy way to understand <i>culverts</i> and <i>fords</i> for OpenStreetMap is about the layers they are on and this dictates the nodes they use.<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p><p class="MsoNormal"><span lang="EN-GB">For a <i>ford</i> the stream/river is at the same level as the road (effectively <i>layer=0</i>) and therefore they are able to share a node.<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p><p class="MsoNormal"><span lang="EN-GB">Because a culvert (<i>layer=-1</i>) is not on the same level as the road but passes underneath so it cannot share a node with the road and therefore the culvert is attributed to the river/stream with a node either side of the road.<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p><p class="MsoNormal"><span lang="EN-GB">With a <i>bridge</i> the road (<i>layer 1</i>) is not on the same level with the stream/river so again cannot share a node and therefore the bridge is attributed to the road with a node at each end of the bridge.<u></u><u></u></span></p><p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p><p class="MsoNormal"><span lang="EN-GB">Hope this will be of help in understanding the problem.<u></u><u></u></span></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Sent from <a href="https://go.microsoft.com/fwlink/?LinkId=550986" target="_blank">Mail</a> for Windows 10</p><p class="MsoNormal"><u></u> <u></u></p></div></div></blockquote></div><br></div>
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