{"id":8400,"date":"2019-03-27T03:25:54","date_gmt":"2019-03-27T02:25:54","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=8400"},"modified":"2019-03-27T20:21:58","modified_gmt":"2019-03-27T19:21:58","slug":"the-arcgis-spatial-temporal-cube-1-discovery","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/the-arcgis-spatial-temporal-cube-1-discovery\/","title":{"rendered":"The ArcGis spatial-temporal cube: 1- discovery"},"content":{"rendered":"\n

One of the GIS areas where much remains to be done is\nthe domain of time analysis. Indeed, if almost all the\navailable tools focus on the spatial evolution of a phenomenon, one finds\noneself quite helpless when it comes to visualizing or analysing a phenomenon\nthat, also, evolves as a function of time. <\/p>\n\n\n\n

We have had, for quite a long time,  animation tools that allow us to see a\nsequence of maps and perceive changes as a function of time. But,\nalthough useful for communication, these tools do not allow any serious data\nanalysis. <\/p>\n\n\n\n\n\n\n\n

We will discuss, in a series of articles, the ArcMap and\nArcGis Pro new available tools as Time Pattern Mining Toolbox. Firstly,\nwe will follow an example, with ArcGis Pro and then, with ArcMap.\n<\/p>\n\n\n\n

What is a Spatial-Temporal\nCube?<\/strong> \n\nThe following image\nsummarizes the answer to this question. \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

On the left we have our points. They\nare distributed on the XY space and it is this distribution we, usually, study\nand analyse with the ArcGis tools. But\nfor a same location, we have several points that correspond to a different\nmoment. That is why the points are distributed, also, on the Z axis\nwhich corresponds to the time. <\/p>\n\n\n\n

The spatial-temporal cube will allow us to analyse the\ndistribution of our points on these three axes. <\/p>\n\n\n\n

First important thing to remember: The tools we will see in\nrelation with the space-time cube do not allow analysing a given phenomenon\nfrom its attributes.<\/strong> They are limited to the\nanalysis of the occurrence or not of a phenomenon (the point exists or does not\nexist).<\/strong> <\/p>\n\n\n\n

The process is simple; we will determine a box size (bin), such\nas the pixels or the cells of the rasters, but 3 dimensional. And\nwe will determine the number of points contained in each box. It is\nthis number that we will visualize and analyze. \n\nLet’s take an example, which\nwill serve us to follow the process in detail. We have weather forecasts\nthat contain wind gust forecasts. These forecasts for 8 days,\nevery 3 hours for an area encompassing Brittany.  \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nAn\noverview of the attribute table allows viewing the \u00ab\u00a0gust\u00a0\u00bb attribute\nwhich corresponds to the speed (in knots) of wind gusts, as well as a\n\u00ab\u00a0DateTime\u00a0\u00bb field which indicates the Date and the hour of each\nforecast.   \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Maybe, one day we will be able to analyse the bursts\nvalues distribution as a function of time. For\nthe time being, since we are limited to the study of the occurrence of points,\nwe can, for example, define a speed threshold that seems risky and analyse the\ndistribution of points that exceed this threshold value. <\/p>\n\n\n\n

If we set the threshold value of 20 knots, we will create a\nnew data layer with the points for which this value is exceeded. The points\nwhere this value is not exceeded will not be present. To\nthis end, we select by attributes, gust> = 20, and export the selected\npoints. <\/p>\n\n\n\n

Now, we have a layer to build our cube. <\/p>\n\n\n\n

Creation of the spatial-temporal\ncube<\/strong> \n\nTo build the cube, which will\nbe stored in a NetCDF (.nc) format, we will use the Create\nSpatio-Temporal Cube<\/em><\/strong> tool in the Spatiotemporal Models Explorer<\/em><\/strong>\ntoolbox .<\/em><\/strong><\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nOnce\nlaunched the command, the parameter window appears. \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The input entities<\/em> correspond to our burst\nselection layer> 20 knots. <\/p>\n\n\n\n

The output spatial-temporal<\/em> cube will be our cube.\n<\/p>\n\n\n\n

The time field<\/em> will be used to define the Z axis. It\nis absolutely mandatory to set a Date field. For\nthose who are still in shapefiles, remember their Date fields can only contain\nthe date but not the time. If you are going to work with\ntime steps less than the day long, you must have a geodatabase entity class.\n<\/p>\n\n\n\n

For now, we do not have a template cube on which to retrieve\nthe other information. If we make a series of cubes,\nthe first one will serve as model, we must verify that the steps and the boxes locations\nwill be the same for all cubes produced. <\/p>\n\n\n\n

The time interval<\/em> is the size of the cube boxes on the\nZ axis. In other words, the time step that we will apply to our analysis.\nIn our example, the forecasts time step is 3 hours.\nA box size of 12 hours will produce 16 time steps in Z. A box\nsize of 24 hours, will produce 8. <\/p>\n\n\n\n

One of the constraints of the cube is that there must be at\nleast 10 time steps. We will choose the time step of\n12 hours. <\/p>\n\n\n\n

The distance interval<\/em> is the cell size in the XY plane.\n<\/p>\n\n\n\n

If you do not fill one or both intervals, the program\ncalculates it by default. <\/p>\n\n\n\n

Visualization of the spatial-temporal\ncube<\/strong> <\/p>\n\n\n\n

To visualize the cube you have to download a toolbox\ncontaining two tools: one that allows visualizing the cube in 2D and another\nthat allows visualizing it in 3D.
\nThe\ntoolkit can be downloaded from http:\/\/esriurl.com\/SpaceTimeCubeUtilities<\/a>\n. \n\nOnce downloaded and\nuncompressed, you can add it to the geoprocessor by clicking on the Ribbon\nInsert -> Toolbox  \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

We will see the visualization in 3D. \n\nYou must have a 3D window\n(Scene) in your project. If\nyou do not have one, click Insert-> New Scene   \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

You must remove the reference to an elevation layer.\nIndeed, if you do not do this, the columns of the cube will\nbe displayed relative to the ground level and you will lose visibility of the\ncorrespondence of the different time steps. <\/p>\n\n\n\n

In the Content panel, click on your scene -> properties\n-> Elevation surface, deploy Ground and delete all services present.\n\n\nExecute the visualization\ncommand of the spatial-temporal cube in 3D:  \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Check the cube you have just created. Give\na name to your visualization layer. <\/p>\n\n\n\n

At this stage, in the variables to display, you will only\nhave Count<\/strong>. In  the next article we will discuss how to use\nother variables after using the Hot Spot Analysis<\/em><\/strong> command .\n\n\nAfterwards, depending on your\ngraphics map, you will have the following result:   \n\n\n\n<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

You can navigate in 3D on the screen to visualize\nwhere are the time steps that exceed the most, the burst threshold value.  But this remains a visual\nevaluation. <\/p>\n\n\n\n

To statistically determine the number of overshoots, the Emerging\nHot Spot Analysis<\/em><\/strong> command provides the standard deviation of the\nresults. <\/p>\n\n\n\n

We will discuss this topic in the next article.\n<\/p>\n","protected":false},"excerpt":{"rendered":"

One of the GIS areas where much remains to be done is the domain of time analysis. Indeed, if almost all the available tools focus on the spatial evolution of a phenomenon, one finds oneself quite…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"give_campaign_id":0,"_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_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[1260],"tags":[],"class_list":["post-8400","post","type-post","status-publish","format-standard","hentry","category-non-classe-en"],"aioseo_notices":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p6XU0A-2bu","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/8400","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/comments?post=8400"}],"version-history":[{"count":0,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/8400\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/media?parent=8400"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/categories?post=8400"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/tags?post=8400"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}