Check out the latest version of Routino: svn co http://routino.org/svn/trunk routino
Contents of /trunk/doc/html/data.html
Parent Directory
| 
Revision Log
Revision 737 -
(show annotations)
(download)
(as text)
Mon May 30 12:51:08 2011 UTC (13 years, 10 months ago) by amb
File MIME type: text/html
File size: 6300 byte(s)
Mon May 30 12:51:08 2011 UTC (13 years, 10 months ago) by amb
File MIME type: text/html
File size: 6300 byte(s)
Run a spelling check on the documentation.
| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| 2 | <HTML> |
| 3 | |
| 4 | <!-- |
| 5 | Routino documentation - data |
| 6 | |
| 7 | Part of the Routino routing software. |
| 8 | |
| 9 | This file Copyright 2008-2011 Andrew M. Bishop |
| 10 | |
| 11 | This program is free software: you can redistribute it and/or modify |
| 12 | it under the terms of the GNU Affero General Public License as published by |
| 13 | the Free Software Foundation, either version 3 of the License, or |
| 14 | (at your option) any later version. |
| 15 | |
| 16 | This program is distributed in the hope that it will be useful, |
| 17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 19 | GNU Affero General Public License for more details. |
| 20 | |
| 21 | You should have received a copy of the GNU Affero General Public License |
| 22 | along with this program. If not, see http://www.gnu.org/licenses/. |
| 23 | --> |
| 24 | |
| 25 | <HEAD> |
| 26 | <TITLE>Routino : Data</TITLE> |
| 27 | <META http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
| 28 | <LINK href="style.css" type="text/css" rel="stylesheet"> |
| 29 | </HEAD> |
| 30 | |
| 31 | <BODY> |
| 32 | |
| 33 | <!-- Header Start --> |
| 34 | |
| 35 | <div class="header" align="center"> |
| 36 | |
| 37 | <h1>Routino : Data</h1> |
| 38 | |
| 39 | <hr> |
| 40 | </div> |
| 41 | |
| 42 | <!-- Header End --> |
| 43 | |
| 44 | <!-- Content Start --> |
| 45 | |
| 46 | <div class="content"> |
| 47 | |
| 48 | <h2><a name="H_1_1"></a>Data</h2> |
| 49 | |
| 50 | A router relies on data to be able to find a route. |
| 51 | |
| 52 | <h3><a name="H_1_1_1"></a>OpenStreetMap Data</h3> |
| 53 | |
| 54 | The data that is collected by the OpenStreetMap project consists of |
| 55 | <em>nodes</em>, <em>ways</em> and <em>relations</em>. |
| 56 | <dl> |
| 57 | <dt>Node |
| 58 | <dd>A node is a point that has a latitude and longitude and attributes that |
| 59 | describe what type of point it is (part of a way or a place of interest for |
| 60 | example). |
| 61 | <dt>Way |
| 62 | <dd>A way is a collection of nodes that when joined together define something |
| 63 | (for example a road, a railway, a boundary, a building, a lake etc). The |
| 64 | ways also have attributes that define them (speed limits, type of road and |
| 65 | restrictions for example). |
| 66 | <dt>Relation |
| 67 | <dd>A relation is a collection of items (usually ways) that are related to |
| 68 | each other for some reason (highways that make up a route for example). |
| 69 | </dl> |
| 70 | |
| 71 | The |
| 72 | <a class="ext" title="OpenStreetMap Wiki" href="http://wiki.openstreetmap.org/wiki/Main_Page">OpenStreetMap Wiki</a> |
| 73 | explains the data much better than I can. |
| 74 | |
| 75 | <h3><a name="H_1_1_2"></a>Router Data</h3> |
| 76 | |
| 77 | The information that is needed by a routing algorithm is only a subset of the |
| 78 | information that is collected by the OpenStreetMap project. For routing what is |
| 79 | required is information about the location of roads (or other highways), the |
| 80 | connections between the highways and the properties of those highways. |
| 81 | <dl> |
| 82 | <dt>Location of highways (nodes) |
| 83 | <dd>The locations of things is provided by the nodes from the OpenStreetMap |
| 84 | data. The nodes are the only things that have coordinates in |
| 85 | OpenStreetMap and everything else is made up by reference to them. Not |
| 86 | all of the nodes are useful, only the ones that are part of highways. The |
| 87 | location of the nodes is stored but none of the other attributes are |
| 88 | currently used by the router. |
| 89 | <dt>Location of highways (ways) |
| 90 | <dd>The location of the highways is defined in the OpenStreetMap data by the |
| 91 | ways. Only the highway ways are useful and the other ways are discarded. |
| 92 | What remains is lists of nodes that join together to form a section of |
| 93 | highway. This is further split into <em>segments</em> which are |
| 94 | individual parts of a way connected by two nodes. |
| 95 | <dt>Properties of highways (tags) |
| 96 | <dd>The ways that belong to highways are extracted from the data in the |
| 97 | previous step and for each way the useful information for routing is |
| 98 | stored. For the router the useful information is the type of highway, the |
| 99 | speed limit, the allowed types of transport and other restrictions |
| 100 | (one-way, minimum height, maximum weight etc). |
| 101 | <dt>Connections between highways |
| 102 | <dd>The connections between highways are defined in the OpenStreetMap data by |
| 103 | ways that share nodes. Since the ways may join in the middle and not just |
| 104 | the ends it is the segments defined above that are not part of the |
| 105 | OpenStreetMap data that are most important. |
| 106 | </dl> |
| 107 | |
| 108 | The information that is extracted from the OpenStreetMap data is stored in an |
| 109 | optimised way that allows the routing to be performed quickly. |
| 110 | |
| 111 | <h3><a name="H_1_1_3" title="Data Tags"></a>Interpreting Data Tags</h3> |
| 112 | |
| 113 | The <em>tags</em> are the information that is attached to the nodes and ways in |
| 114 | OpenStreetMap. The router needs to interpret these tags and use them when |
| 115 | deciding what type of traffic can use a highway (for example). |
| 116 | <p> |
| 117 | |
| 118 | There are no well defined rules in OpenStreetMap about tagging, but there is |
| 119 | guidance on the |
| 120 | <a class="ext" title="Map Features" href="http://wiki.openstreetmap.org/index.php/Map_Features">OpenStreetMap Wiki "Map_Features"</a> |
| 121 | page. This describes a set of recommended tags but these are not universally used |
| 122 | so it is up to each application how to interpret them. |
| 123 | <p> |
| 124 | |
| 125 | The <a title="Tagging" href="tagging.html">tagging rules</a> that the router |
| 126 | uses are very important in controlling how the router works. With Routino the |
| 127 | data tags can be modified when the data is imported to allow customisation of |
| 128 | the information used for routing. |
| 129 | |
| 130 | |
| 131 | <h3><a name="H_1_1_4" title="Problems With Data"></a>Problems With OpenStreetMap Data</h3> |
| 132 | |
| 133 | The route that can be found is only as good as the data that is available. This |
| 134 | is not intended as a criticism of the OpenStreetMap data; it is generally good. |
| 135 | <p> |
| 136 | There are some problems that are well known and which affect the router. For |
| 137 | example highways might be missing because nobody has mapped them. A highway may |
| 138 | be wrongly tagged with incorrect properties, or a highway might be missing |
| 139 | important tags for routing (e.g. speed limits). There can also be problems |
| 140 | with highways that should join but don't because they do not share nodes. |
| 141 | <p> |
| 142 | A lot of these problems can be found using the interactive data visualiser that |
| 143 | uses the same Routino routing database. |
| 144 | |
| 145 | |
| 146 | </div> |
| 147 | |
| 148 | <!-- Content End --> |
| 149 | |
| 150 | <!-- Footer Start --> |
| 151 | |
| 152 | <div class="footer" align="center"> |
| 153 | <hr> |
| 154 | |
| 155 | <address> |
| 156 | © Andrew M. Bishop = <amb "at" gedanken.demon.co.uk> |
| 157 | </address> |
| 158 | |
| 159 | </div> |
| 160 | |
| 161 | <!-- Footer End --> |
| 162 | |
| 163 | </BODY> |
| 164 | |
| 165 | </HTML> |