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Understanding electronic nautical charts before using them in a GIS<\/a>
- Introduction<\/a><\/li>
- 1. A very strict international standard<\/a><\/li>
- 2. ENCs are not \u201clayers,\u201d but objects.<\/a>
  - 2.1 Object-oriented logic<\/a><\/li>
  - 2.2 Coded and non-explicit attributes<\/a><\/li><\/ul><\/li>
  - 3. A strict separation between geometry and information<\/a>
    - 3.1 Shared geometries<\/a><\/li>
    - 3.2 No embedded symbolization<\/a><\/li><\/ul><\/li>
    - 4. The concept of \u201cPurpose\u201d and scale<\/a><\/li>
    - 5. A logic designed for safety, not for analysis<\/a><\/li>
    - 6. Why a dedicated plugin is necessary in QGIS<\/a><\/li>
    - Conclusion<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n
      <\/span>Understanding electronic nautical charts before using them in a GIS<\/span><\/h1>\n\n\n\n
      \n\n\n\n
      <\/span>Introduction<\/span><\/h2>\n\n\n\n
      ENC \u2013 Electronic Navigational Charts are now the global standard for professional maritime navigation.<\/p>\n\n\n\n
      Produced by national hydrographic services, they comply with strict standards defined by the International Hydrographic Organization (IHO).<\/p>\n\n\n\n
      \n\n\n\n\n\n\n
      \n\n\n\n
      However, when attempting to use them in a GIS such as QGIS, one thing quickly becomes clear:<\/p>\n\n\n\n
      \n
      an ENC is not a conventional vector layer.<\/p>\n<\/blockquote>\n\n\n\n
      It is neither an enhanced shapefile<\/a>, nor a simple GeoPackage<\/a>, nor even an ordinary spatial database.<\/p>\n\n\n\n
      ENCs are complex information objects, designed primarily for navigation, not for GIS analysis.<\/p>\n\n\n\n
      This article aims to explain why ENCs are complex, and how this complexity explains the difficulties\u2014but also the richness\u2014of using them in QGIS.<\/p>\n\n\n\n
      \n\n\n\n
      <\/span>1. A very strict international standard<\/span><\/h2>\n\n\n\n
      ENC are defined by the S-57 standard (and more recently S-101), published by the IHO.<\/p>\n\n\n\n
      This standard requires:<\/p>\n\n\n\n
      \n
      a precise data structure<\/li>\n\n\n\n
      standardized vocabulary<\/li>\n\n\n\n
      strict interpretation rules<\/li>\n\n\n\n
      a clear separation between:\n
      \n
      geometry<\/li>\n\n\n\n
      semantics<\/li>\n\n\n\n
      presentation<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n
      👉 Result:<\/p>\n\n\n\n
      the data is consistent worldwide, but difficult to divert from its original use.<\/p>\n\n\n\n
      \n\n\n\n
      <\/span>2. ENCs are not \u201clayers,\u201d but objects.<\/span><\/h2>\n\n\n\n
      <\/span>2.1 Object-oriented logic<\/span><\/h3>\n\n\n\n
      In an ENC:<\/p>\n\n\n\n
      \n
      each entity is a nautical object<\/li>\n\n\n\n
      each object has:\n
      \n
      a standardized type (e.g., DEPARE, COALNE, LNDARE)<\/li>\n\n\n\n
      a geometry<\/li>\n\n\n\n
      a list of coded attributes<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n
      Examples of objects:<\/p>\n\n\n\n
      \n
      depth zones<\/li>\n\n\n\n
      navigation aids<\/li>\n\n\n\n
      isolated hazards<\/li>\n\n\n\n
      coastlines<\/li>\n\n\n\n
      restricted areas<\/li>\n<\/ul>\n\n\n\n
      👉 Unlike traditional GIS,<\/p>\n\n\n\n
      \n
      we do not start with a geometry but with a semantic object.<\/p>\n<\/blockquote>\n\n\n\n
      \n\n\n\n
      <\/span>2.2 Coded and non-explicit attributes<\/span><\/h3>\n\n\n\n
      S-57 attributes:<\/p>\n\n\n\n
      \n
      are often digitally coded<\/li>\n\n\n\n
      require correspondence tables<\/li>\n\n\n\n
      only make sense within the context of the standard<\/li>\n<\/ul>\n\n\n\n
      Example:<\/p>\n\n\n\n
      \n
      CATOBS = 3<\/li>\n\n\n\n
      WATLEV = 2<\/li>\n<\/ul>\n\n\n\n
      Without IHO documentation, these values are unreadable.<\/p>\n\n\n\n
      \n\n\n\n
      <\/span>3. A strict separation between geometry and information<\/span><\/h2>\n\n\n\n
      <\/span>3.1 Shared geometries<\/span><\/h3>\n\n\n\n
      In an ENC:<\/p>\n\n\n\n
      \n
      multiple objects can share the same geometry<\/li>\n\n\n\n
      lines and nodes are stored separately<\/li>\n\n\n\n
      topology is implicit<\/li>\n<\/ul>\n\n\n\n
      👉 This allows for:<\/p>\n\n\n\n
      \n
      high accuracy<\/li>\n\n\n\n
      efficient updating<\/li>\n<\/ul>\n\n\n\n
      👉 But it complicates:<\/p>\n\n\n\n
      \n
      direct import into a GIS<\/li>\n\n\n\n
      understanding spatial relationships<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/span>3.2 No embedded symbolization<\/span><\/h3>\n\n\n\n
      ENC charts do not contain their own graphic style.<\/p>\n\n\n\n
      Visual representation:<\/p>\n\n\n\n
      \n
      depends on the navigation system (ECDIS)<\/li>\n\n\n\n
      follows complex rules (S-52)<\/li>\n<\/ul>\n\n\n\n
      In QGIS:<\/p>\n\n\n\n
      \n
      styles must be recreated<\/li>\n\n\n\n
      understand which rules apply depending on the context<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/span>4. The concept of \u201cPurpose\u201d and scale<\/span><\/h2>\n\n\n\n
      An ENC is not universal:<\/p>\n\n\n\n
      \n
      it is produced for a specific use, called Purpose.<\/p>\n<\/blockquote>\n\n\n\n
      Examples:<\/p>\n\n\n\n
      \n
      general view<\/li>\n\n\n\n
      coastal navigation<\/li>\n\n\n\n
      port approach<\/li>\n\n\n\n
      detailed port<\/li>\n<\/ul>\n\n\n\n
      Each ENC:<\/p>\n\n\n\n
      \n
      has a target scale<\/li>\n\n\n\n
      is not intended to be used out of context<\/li>\n<\/ul>\n\n\n\n
      👉 In a GIS, displaying all ENCs without filtering produces:<\/p>\n\n\n\n
      \n
      duplicates<\/li>\n\n\n\n
      inconsistencies<\/li>\n\n\n\n
      visual conflicts<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/span>5. A logic designed for safety, not for analysis<\/span><\/h2>\n\n\n\n
      ENC charts are designed to:<\/p>\n\n\n\n
      \n
      avoid human error<\/li>\n\n\n\n
      ensure unambiguous reading<\/li>\n\n\n\n
      comply with priority rules<\/li>\n\n\n\n
      ensure navigational safety<\/li>\n<\/ul>\n\n\n\n
      They are not designed for:<\/p>\n\n\n\n
      \n
      free spatial queries<\/li>\n\n\n\n
      classic GIS joins<\/li>\n\n\n\n
      multi-thematic analyses<\/li>\n<\/ul>\n\n\n\n
      👉 Any GIS exploitation therefore requires:<\/p>\n\n\n\n
      \n
      restructuring<\/li>\n\n\n\n
      interpretation<\/li>\n\n\n\n
      sometimes simplification<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/span>6. Why a dedicated plugin is necessary in QGIS<\/span><\/h2>\n\n\n\n
      Importing an ENC \u201cbrutally\u201d into QGIS often leads to:<\/p>\n\n\n\n
      \n
      dozens of unreadable layers<\/li>\n\n\n\n
      incomprehensible fields<\/li>\n\n\n\n
      fragmented geometries<\/li>\n\n\n\n
      a loss of nautical meaning<\/li>\n<\/ul>\n\n\n\n
      A tool such as S57Manager <\/a>allows you to:<\/p>\n\n\n\n
      \n
      comply with S-57 logic<\/li>\n\n\n\n
      structure data<\/li>\n\n\n\n
      make attributes usable<\/li>\n\n\n\n
      prepare for display and analysis<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/span>Conclusion<\/span><\/h2>\n\n\n\n
      ENC are complex by design.<\/p>\n\n\n\n
      This complexity is not a flaw:<\/p>\n\n\n\n
      \n
      it guarantees reliability<\/li>\n\n\n\n
      international consistency<\/li>\n\n\n\n
      navigation safety<\/li>\n<\/ul>\n\n\n\n
      But for the GIS world, it requires<\/p>\n\n\n\n
      \n
      appropriate tools, a basic understanding of the standard, and an approach that respects nautical logic.<\/p>\n<\/blockquote>\n\n\n\n
      👉 Understanding this complexity is the first step before:<\/p>\n\n\n\n
      \n
      importing into QGIS<\/li>\n\n\n\n
      choosing PostGIS<\/a> or GeoPackage<\/li>\n\n\n\n
      using a specialized plugin such as S57Manager<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      🔗 Articles to follow<\/p>\n\n\n\n
      \n
      S57Manager: managing S-57 ENC data in QGIS with PostGIS<\/em><\/li>\n\n\n\n
      S57Manager: using S-57 ENC data in QGIS with GeoPackage<\/em><\/li>\n\n\n\n
      Importing NOAA ENC nautical charts directly into QGIS with S57Manager<\/em><\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      <\/p>\n","protected":false},"excerpt":{"rendered":"
      Understanding electronic nautical charts before using them in a GIS Introduction ENC \u2013 Electronic Navigational Charts are now the global standard for professional maritime navigation. Produced by national hydrographic services, they comply with strict standards defined…<\/p>\n","protected":false},"author":1,"featured_media":16143,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"sfsi_plus_gutenberg_text_before_share":"","sfsi_plus_gutenberg_show_text_before_share":"","sfsi_plus_gutenberg_icon_type":"","sfsi_plus_gutenberg_icon_alignemt":"","sfsi_plus_gutenburg_max_per_row":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[3931],"tags":[2545,2721],"class_list":["post-16190","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-s57-en","tag-data","tag-s57-en"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t

<\/span>Conclusion<\/span><\/h2>\n\n\n\nENC are complex by design.<\/p>\n\n\n\nThis complexity is not a flaw:<\/p>\n\n\n\n\nit guarantees reliability<\/li>\n\n\n\ninternational consistency<\/li>\n\n\n\n