{"id":77,"date":"2022-08-03T19:13:19","date_gmt":"2022-08-03T19:13:19","guid":{"rendered":"https:\/\/oomap.dna-software.co.uk\/help\/?page_id=77"},"modified":"2023-05-06T16:39:08","modified_gmt":"2023-05-06T16:39:08","slug":"contours","status":"publish","type":"page","link":"https:\/\/oomap.dna-software.co.uk\/help\/details\/contours\/","title":{"rendered":"Contours"},"content":{"rendered":"\n<p>Contour provision is a major enhancement for this version of oomap &#8211; there are globally-available options for contours along with locale-specific higher-quality options.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"825\" height=\"66\" src=\"https:\/\/oomap.dna-software.co.uk\/help\/wp-content\/uploads\/2022\/08\/image-38.png\" alt=\"\" class=\"wp-image-80\" srcset=\"https:\/\/oomap.dna-software.co.uk\/help\/wp-content\/uploads\/2022\/08\/image-38.png 825w, https:\/\/oomap.dna-software.co.uk\/help\/wp-content\/uploads\/2022\/08\/image-38-300x24.png 300w, https:\/\/oomap.dna-software.co.uk\/help\/wp-content\/uploads\/2022\/08\/image-38-768x61.png 768w\" sizes=\"auto, (max-width: 825px) 100vw, 825px\" \/><\/figure>\n\n\n\n<p>Each contour option will select a different contour rendering for the final map.  Some of these options produce a visible preview in the web view, while others do not (due to differences in how they are created).<\/p>\n\n\n\n<p>Apart from &#8220;OS (10m)&#8221;-derived contours, rendered contours all show the direction of slope using downward tags at regular intervals.<\/p>\n\n\n\n<p>As well as &#8220;None&#8221; there are two major classes of contour:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Global, satellite-derived contours<\/strong>.  No pre-rendering is available.<br>SRTM (5m), SRTM (10m), GLO-30 (5m), GLO-30 (10m).<\/li>\n\n\n\n<li><strong>Local, pre-calculated contours<\/strong>.  Pre-rendering is available.<br>OS (10m), LIDAR (5m), LIDAR (10m).<\/li>\n<\/ul>\n\n\n\n<h5 class=\"wp-block-heading\">Global contours<\/h5>\n\n\n\n<p>&#8220;<strong>SRTM<\/strong>&#8221; (Shuttle Radar Topology Mission) contours are available at 5m and 10m vertical intervals, and are derived from a near-global digital elevation model collected by the <a href=\"https:\/\/www2.jpl.nasa.gov\/srtm\/\" data-type=\"URL\" data-id=\"https:\/\/www2.jpl.nasa.gov\/srtm\/\">Space Shuttle in 2000<\/a>.  Data does not extend beyond latitudes 60 degrees N and 60 degrees S.<\/p>\n\n\n\n<p>&#8220;<strong>GLO-30<\/strong>&#8221; contours are also available at 5m and 10m vertical intervals and are derived from an almost complete global digital elevation model (<a href=\"https:\/\/portal.opentopography.org\/raster?opentopoID=OTSDEM.032021.4326.3\" data-type=\"URL\" data-id=\"https:\/\/portal.opentopography.org\/raster?opentopoID=OTSDEM.032021.4326.3\">Copernicus GLO-30<\/a>) from data collected between 2011 and 2015. <\/p>\n\n\n\n<p>Both datasets have a nominal horizontal resolution of 30m but the GLO-30 set seems to be of higher overall quality (and is more recent).  However, both suffer from land-cover effects &#8211; since they are measuring the radar-derived average heights of the ground, they are affected by tree cover and buildings, in both cases giving artefactually higher readings than expected for the &#8220;true&#8221; terrain.<\/p>\n\n\n\n<p>Because these datasets are global, they are large and also take considerable resources to transform from height data into contours.  Therefore for both, contours are generate on-the-fly when a map rendering is requested.  First, a 1 degree square portion of height data is downloaded if not already available locally, then contours are calculated just for the requested map area.  This process can add 30-60 s to a typically map rendering job &#8211; so be patient!<\/p>\n\n\n\n<h5 class=\"wp-block-heading\">local contours<\/h5>\n\n\n\n<p><strong>OS (10m) <\/strong>&#8211; These are contours from the <a href=\"https:\/\/www.ordnancesurvey.co.uk\/business-government\/products\/terrain-50\" data-type=\"URL\" data-id=\"https:\/\/www.ordnancesurvey.co.uk\/business-government\/products\/terrain-50\">Ordnance Survey<\/a>, covering Great Britain with high-quality but relatively low resolution (50m horizontal grid) data.<\/p>\n\n\n\n<p><strong>LIDAR <\/strong>&#8211; Where other high-resolution digital terrain models (typically produced by airborne LIDAR surveys) are easily available and appropriately licenced, these have been downloaded and pre-processed to generate contour datasets that can be rendered at 5m or 10m vertical spacing.  Current coverage includes:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Most of England and Wales (~ 98% coverage).  This is a high-quality dataset that has been post-processed to remove many artefacts, with high horizontal resolution that has been downsampled to 10m horizontal precision.<\/li>\n\n\n\n<li>Some of Scotland, covering most of the population centres and more<\/li>\n\n\n\n<li>Northern Ireland<\/li>\n\n\n\n<li>France<\/li>\n\n\n\n<li>Belgium<\/li>\n\n\n\n<li>Austria<\/li>\n\n\n\n<li>Luxembourg<\/li>\n\n\n\n<li>New Zealand (major population centres only)<\/li>\n\n\n\n<li>Australia (major population centres only)<\/li>\n\n\n\n<li>Canada (parts of Ontario)<\/li>\n<\/ul>\n\n\n\n<p><strong>Other datasets<\/strong> could potentially be similarly processed and made available &#8211; please leave <a href=\"https:\/\/oomap.dna-software.co.uk\/help\/feedback\/\" data-type=\"page\" data-id=\"12\">feedback <\/a>if you know of such a source and would find the data useful.<\/p>\n\n\n\n<p><strong>Copyrights <\/strong>for the contour sources are printed on the final map rendering.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Contour provision is a major enhancement for this version of oomap &#8211; there are globally-available options for contours along with locale-specific higher-quality options. Each contour option will select a different contour rendering for the final map. Some of these options produce a visible preview in the web view, while others do not (due to differences [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":45,"menu_order":25,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-77","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/pages\/77","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/comments?post=77"}],"version-history":[{"count":3,"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/pages\/77\/revisions"}],"predecessor-version":[{"id":168,"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/pages\/77\/revisions\/168"}],"up":[{"embeddable":true,"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/pages\/45"}],"wp:attachment":[{"href":"https:\/\/oomap.dna-software.co.uk\/help\/wp-json\/wp\/v2\/media?parent=77"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}