{"id":1974,"date":"2018-03-29T15:00:59","date_gmt":"2018-03-29T02:00:59","guid":{"rendered":"http:\/\/blogs.lincoln.ac.nz\/gis\/?p=1974"},"modified":"2018-03-29T15:00:59","modified_gmt":"2018-03-29T02:00:59","slug":"where-this-is-no-elevation","status":"publish","type":"post","link":"https:\/\/blogs.lincoln.ac.nz\/gis\/where-this-is-no-elevation\/","title":{"rendered":"Where This Is No Elevation"},"content":{"rendered":"<p><em>This post covers how elevations for dragonfly observation points data for Vanuatu were sourced from a space shuttle mission in 2000.<\/em><\/p>\n<p>For creatures that weigh way <a href=\"https:\/\/www.quora.com\/How-much-does-a-dragonfly-weigh\" target=\"_blank\" rel=\"noopener noreferrer\">less than a gram<\/a>, dragonflies have certainly kept me busy over the years.\u00a0 We&#8217;ve already seen how my colleague, Milen, used some <a href=\"http:\/\/blogs.lincoln.ac.nz\/gis\/2017\/05\/04\/dont-let-that-dragonfly-get-away-offline-mapping-in-vanuatu\/\" target=\"_blank\" rel=\"noopener noreferrer\">offline maps<\/a> on his phone to collect observations in Vanuatu, as well as some <a href=\"http:\/\/blogs.lincoln.ac.nz\/gis\/2018\/03\/22\/taveuni-an-island-torn-in-two\/\" target=\"_blank\" rel=\"noopener noreferrer\">mapping complications in Taveuni<\/a>.\u00a0 And there&#8217;s more to come as we work on mapping species diversity across the Pacific.<\/p>\n<p>But now another installment in the continuing <a href=\"http:\/\/mentalfloss.com\/article\/86739\/25-dramatic-dragonfly-nicknames-around-us\" target=\"_blank\" rel=\"noopener noreferrer\">dragonfly <\/a>story.\u00a0 After Milen collected his observations in Vanuatu, he came back with a simple request: could he please have the elevations of all the observations?\u00a0 My first reaction was, ummmm, sure, easy, but I haven&#8217;t got any elevation data for Vanuatu!\u00a0 I haven&#8217;t even got any contours.\u00a0 So what&#8217;s a spatial analyst to do?<\/p>\n<p>Like most, my first stop was Google, but to no avail.\u00a0 Unlike New Zealand, such data aren&#8217;t easily available.\u00a0 I found a few sites, but no actual data I could use.\u00a0 <a href=\"http:\/\/Koordinates.com\" target=\"_blank\" rel=\"noopener noreferrer\">Koordinates.com<\/a> has tons of data and lots for Oceania, but none for Vanuatu.\u00a0 These sites had maps and some very nice pictures, but no actual data:<\/p>\n<ul>\n<li><a href=\"http:\/\/www.floodmap.net\/Elevation\/CountryElevationMap\/?ct=VU\" target=\"_blank\" rel=\"noopener noreferrer\">Floodmap.net<\/a><\/li>\n<\/ul>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/VanuatuElevationMap.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1975\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/VanuatuElevationMap.jpg\" alt=\"\" width=\"516\" height=\"596\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/VanuatuElevationMap.jpg 516w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/VanuatuElevationMap-260x300.jpg 260w\" sizes=\"auto, (max-width: 516px) 100vw, 516px\" \/><\/a><\/p>\n<ul>\n<li><a href=\"http:\/\/elevation.maplogs.com\/poi\/vanuatu.53796.html\" target=\"_blank\" rel=\"noopener noreferrer\">Maplogs.com<\/a><\/li>\n<\/ul>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Caldera.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1976\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Caldera.jpg\" alt=\"\" width=\"604\" height=\"606\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Caldera.jpg 604w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Caldera-300x300.jpg 300w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Caldera-150x150.jpg 150w\" sizes=\"auto, (max-width: 604px) 100vw, 604px\" \/><\/a><\/p>\n<p>While these are raster images, they don&#8217;t have any real elevation data.\u00a0 Then I remembered that, many years ago, there was a space shuttle mission that aimed to map elevations for 80% of the earth&#8217;s surface.\u00a0 Can we get our hands on it?<\/p>\n<p><a href=\"https:\/\/www.youtube.com\/watch?v=47MKGOPP4Zo\" target=\"_blank\" rel=\"noopener noreferrer\">Yes, we can.<\/a><\/p>\n<p>The <a href=\"https:\/\/www2.jpl.nasa.gov\/srtm\/mission.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Shuttle Radar Topography Mission<\/a> (SRTM) flew in 2000 and used radar to map elevation.\u00a0 The <a href=\"https:\/\/www.google.com\/search?tbm=isch&amp;source=hp&amp;biw=1364&amp;bih=645&amp;ei=TrS4WuW9BpGM8gX78424CA&amp;q=shuttle+endeavour&amp;oq=shuttle+endeav&amp;gs_l=img.3.1.0l2j0i5i30k1l7j0i8i30k1.959.3704.0.5486.17.14.1.0.0.0.289.2196.0j2j8.10.0....0...1ac.1.64.img..6.11.2196.0..0i10k1j0i8i10i30k1j0i30k1.0.U3yKEqIaOLQ\" target=\"_blank\" rel=\"noopener noreferrer\">shuttle Endeavour<\/a> flew upside down with its cargo bay open.\u00a0 Inside was the radar transmitter as well as a receiver.\u00a0 At the end of a 60 metre mast was a second receiver.\u00a0 The two receivers allowed the two responses to be reconciled with elevation at the land surface dropping out &#8211; this is called <a href=\"https:\/\/www2.jpl.nasa.gov\/srtm\/instrumentinterferometry.html\" target=\"_blank\" rel=\"noopener noreferrer\">interferometry<\/a>.\u00a0 In a sense, it&#8217;s like our two eyes, slightly separated, that give us a sense of depth perception.<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/shuttlewaves1.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1977\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/shuttlewaves1.gif\" alt=\"\" width=\"402\" height=\"218\" \/><\/a><\/p>\n<p>What originally came out of the data was a roughly 90 m resolution DEM of most of the earth&#8217;s surface (it varies with latitude) and freely available on the internet.\u00a0 Milen was happy with a 90 m resolution, so let&#8217;s go to Vanuatu!<\/p>\n<p><a href=\"http:\/\/srtm.csi.cgiar.org\/SELECTION\/inputCoord.asp\" target=\"_blank\" rel=\"noopener noreferrer\">This site<\/a> allows anyone to search for these data:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Search.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1978\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Search.jpg\" alt=\"\" width=\"904\" height=\"694\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Search.jpg 904w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Search-300x230.jpg 300w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Search-768x590.jpg 768w\" sizes=\"auto, (max-width: 904px) 100vw, 904px\" \/><\/a><\/p>\n<p>Three search options: Multiple Selection, Enable Mouse Drag and Input Coordinates.\u00a0 I could see what I was after so I chose to click and drag:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Window.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1979 alignleft\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Window.jpg\" alt=\"\" width=\"110\" height=\"141\" \/><\/a>This is probably a much larger area than I need but I&#8217;ve selected this just to be thorough.\u00a0 I know my data are spread across several islands.<\/p>\n<p>We should look at the observation data next to make sure we only grab what we need.<\/p>\n<p>So here are my points, 92 in all spread across four islands.\u00a0 Milen was busy!<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Points.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1982\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Points.jpg\" alt=\"\" width=\"702\" height=\"559\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Points.jpg 702w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Points-300x239.jpg 300w\" sizes=\"auto, (max-width: 702px) 100vw, 702px\" \/><\/a><\/p>\n<p>I&#8217;ll need to ensure I get data that cover them all (actually, I&#8217;m just after three of the islands as Milen said not to worry about the northern most one).\u00a0\u00a0 Back in the SRTM search window, I got several results &#8211; here&#8217;s an example of one of the them:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1983\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download.jpg\" alt=\"\" width=\"1343\" height=\"360\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download.jpg 1343w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download-300x80.jpg 300w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download-1024x274.jpg 1024w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Download-768x206.jpg 768w\" sizes=\"auto, (max-width: 1343px) 100vw, 1343px\" \/><\/a><\/p>\n<p>So there&#8217;s a description at left, with file names and details, the Location is shown in the middle and an image of the actual coverage area at right.\u00a0 As it turns out, this is one of the ones I need.\u00a0 The southermost island I need, Aneityum, is on the tile just below.\u00a0 I can download this file by clicking on &#8220;Data Download (HTTP)&#8221; button at the bottom and delivered to my Dowload folder is a zipped file of the data.\u00a0 I do this for both tiles and, almost out of nowhere (well, from roughly 400 km above sea level), I&#8217;ve got the data I need:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/WithElev.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1984\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/WithElev.jpg\" alt=\"\" width=\"1021\" height=\"579\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/WithElev.jpg 1021w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/WithElev-300x170.jpg 300w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/WithElev-768x436.jpg 768w\" sizes=\"auto, (max-width: 1021px) 100vw, 1021px\" \/><\/a><\/p>\n<p>Great &#8211; almost there.\u00a0 Notice how there&#8217;s only half of the data for New Caledonia at lower left as well as the top half of Espiritu Santo &#8211; these are just the extents of the two tiles.\u00a0 Also, these DEMs are TIF files, or to be more exact, GeoTiffs.\u00a0 These are your standard image files but they have both position data built in and pixel values that relate to physical attributes rather than just colour, elevation in this case.\u00a0 We can treat them as any other layer in ArcGIS.<\/p>\n<p>Next step, I&#8217;d like to extract the elevation values for each point from the grid cell they are within.\u00a0 Two ways to do this:<\/p>\n<ul>\n<li><a href=\"http:\/\/desktop.arcgis.com\/en\/arcmap\/10.3\/tools\/spatial-analyst-toolbox\/extract-values-to-points.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Extract Values to Points<\/a><\/li>\n<li><a href=\"http:\/\/desktop.arcgis.com\/en\/arcmap\/10.3\/tools\/geostatistical-analyst-toolbox\/extract-values-to-table.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Extract Values to Table<\/a><\/li>\n<\/ul>\n<p>Both of these tools do the same thing &#8211; extract values from grid cells at points &#8211; the difference is the output.\u00a0 The first tool creates a new spatial layer with the elevations added &#8211; sort of a vector to raster spatial join.\u00a0 The second does that same but just outputs a table.\u00a0 I could use either here, but since all Milen&#8217;s interested in is having the data in a table, I went the second route:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Extract.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1985\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Extract.jpg\" alt=\"\" width=\"559\" height=\"453\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Extract.jpg 559w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/Extract-300x243.jpg 300w\" sizes=\"auto, (max-width: 559px) 100vw, 559px\" \/><\/a><\/p>\n<p>The input Features are my dragonfly observations and the Input rasters are my elevation grids.\u00a0 I can save the table as a standalone DBF table or as a table in a geodatabase.\u00a0 To finish things off, I&#8217;ll use the <a href=\"http:\/\/desktop.arcgis.com\/en\/arcmap\/10.3\/tools\/conversion-toolbox\/table-to-excel.htm\" target=\"_blank\" rel=\"noopener noreferrer\">Table to Exce<\/a>l tool &#8211; this handy tool exports any table directly to Excel which saves a bit of work.\u00a0 And here&#8217;s the final result &#8211; a spreadsheet I can send to Milen:<\/p>\n<p><a href=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/SS.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1986\" src=\"https:\/\/d-blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/SS.jpg\" alt=\"\" width=\"1023\" height=\"663\" srcset=\"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/SS.jpg 1023w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/SS-300x194.jpg 300w, https:\/\/blogs.lincoln.ac.nz\/gis\/wp-content\/uploads\/sites\/3\/2018\/03\/SS-768x498.jpg 768w\" sizes=\"auto, (max-width: 1023px) 100vw, 1023px\" \/><\/a><\/p>\n<p>This spreadsheet has well over 50 columns so I&#8217;ve just showed the elevation column that was added by the tool.<\/p>\n<p>So, to recap.\u00a0 To get the elevations for a series of points, we downloaded some SRTM elevation data, used the Extract Values to Table tool, then exported that table to Excel, and job done.\u00a0 Nice that we could make use of data collected by the shuttle to cover areas where there are no data.<\/p>\n<p>As a sidenote, I used the same SRTM data to get the elevations in Taveuni, with slightly more work <a href=\"http:\/\/blogs.lincoln.ac.nz\/gis\/2018\/03\/22\/taveuni-an-island-torn-in-two\/\" target=\"_blank\" rel=\"noopener noreferrer\">as we&#8217;ve seen<\/a>.<\/p>\n<p>Once again, those pesky dragonflies have kept me busy, but in a good way.\u00a0 I just haven&#8217;t figured out how to get a charge code out of them.<\/p>\n<p>C    \t<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This post covers how elevations for dragonfly observation points data for Vanuatu were sourced from a space shuttle mission in 2000. For creatures that weigh way less than a gram, dragonflies have certainly kept me busy over the years.\u00a0 We&#8217;ve already seen how my colleague, Milen, used some offline maps on his phone to collect [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1974","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/1974","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/comments?post=1974"}],"version-history":[{"count":0,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/1974\/revisions"}],"wp:attachment":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/media?parent=1974"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/categories?post=1974"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/tags?post=1974"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}