{"id":8485,"date":"2019-04-08T01:52:25","date_gmt":"2019-04-07T23:52:25","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=8485"},"modified":"2019-04-08T08:18:14","modified_gmt":"2019-04-08T06:18:14","slug":"the-processing-algorithms-with-the-qgis-2-8-graphic-modeller-adding-algorithms-in-the-graphic-modeller","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/the-processing-algorithms-with-the-qgis-2-8-graphic-modeller-adding-algorithms-in-the-graphic-modeller\/","title":{"rendered":"The processing algorithms with the QGis 2.8 Graphic Modeller-Adding algorithms in the graphic modeller"},"content":{"rendered":"\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nThe\nalgorithms are added in   the graphic modeller as if they were data input.\nSimply select algorithms<\/em><\/strong> tab instead of Inputs<\/em><\/strong> data,\nto observe the corresponding display in the  Box<\/em><\/strong>processing<\/em><\/strong>tool\n<\/em><\/strong>display.<\/em><\/strong><\/p>\n\n\n\n

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

Once the algorithm to be added is found, double- click, or glide toward the graphic window of the Modeller. To search the algorithm you can do it \u00a0 as you would in the processing toolbox, typing the name in the search box at the top of the algorithm tab. <\/p>\n\n\n\n\n\n\n\n

In fact , the algorithms<\/em><\/strong> tab is the window processing toolbox\nopened in the modeller . This box display has two settings : Advanced and\nSimplified. \n\n[ caption id = \u00ab\u00a0attachment_1691″ align\n= \u00a0\u00bb aligncenter \u00a0\u00bb width = \u00ab\u00a0264\u00a0\u00bb]  \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\nDisplay\nwith advanced interface [ \/ caption] \n\n\n\n<\/p>\n\n\n\n

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

settings display\nwith simplified interface [\/ caption] <\/p>\n\n\n\n

The interface parameter that is currently in use in the processing\ntoolbox determines how will be organized   the algorithms in the graphic modeller\n. This parameter cannot be exchanged in the graphic modeller. To change the\nsetting , the graphic modeller has to be stopped, the interface parameter\nexchanged in the processing toolbox and the graphic modeller relaunched. Besides\nthis, the algorithms search follows the same approach in the processing toolbox:\ntype the name or a part of the name of the processing being searched and you\nwill have the list of available processings. <\/p>\n\n\n\n

In the algorithms tab, there is a special category called Specific\ntools <\/em><\/strong> to the<\/em><\/strong> modeller<\/em><\/strong>\n. The three tools – calculator , Raster layer boundaries and Vector layer\nboundaries – do not appear in the processing toolbox. These are tools that only\nmake sense when are used under the graphic modeller. <\/p>\n\n\n\n

The calculator tool is the most commonly used of the three tools . It\nallows performing arithmetic calculations in the digital outputs of others\nalgorithms , and insert them as an entry in other processings of the same model\n. \n\nWhen you add the calculator to the graphic window,\nthe info window lists the available digital values within the model . The\nwindow below allows entering a formula by using the letters assigned to each\ndigital value as variables. For example , the entered formula in the following\nfigure   displays the only numeric variable of our current model (the\nbuffer distance) and calculates twice this distance (a * 2).  \n\n\n\n<\/p>\n\n\n\n

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

This output of the calculator algorithm can be used as input of another\nalgorithm of this model . \n\nWhen you add an algorithm to the graphical modeller\nwindow, the algorithm settings window opens . The dialog box will be very\nsimilar to the one you would obtain if you were to launch, directly, the tool\nfrom the processing box: you will get the input data, the output data and the tool\nparameters. \n\n\n\n<\/p>\n\n\n\n

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

However, there are some important differences because the graphic modeller\nis an autonomous universe of data entries . The differences are the following: \n\n\u2022 In the input<\/em><\/strong>layers<\/em><\/strong>\nlist you will be limited to those which have been added to the model . \n\n\n\n<\/p>\n\n\n\n

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

\u2022 The Output<\/em><\/strong> field can be left empty if it is an\nintermediate result that will be used as an entry for another algorithm . If\nthe exit is a layer that needs to be saved , enter the name of this layer in\nthe text box . When you name an exit layer , you do not need to provide an\noutput file name . This will be done when the tool is executed . Instead, it is\nenough to enter the layer name (for example , buffer installations<\/em> ).
\nIt has to be correctly understood how do the output algorithm data works: <\/p>\n\n\n\n

  • Since\nthey, only, serve as data intermediaries for the following algorithms : you<\/strong> leave the name empty<\/strong> <\/li>
  • Even if they are used by the following algorithms , you will want to keep the layer produced : you<\/strong> assign an<\/strong> output<\/strong> name.<\/strong> <\/li><\/ul>\n\n\n\n

    \n\n\n\nThis name is not the name of the output file but\nthe label that will be displayed in the execution window of the model when you execute\nit . Remember that in the modeller, while creating the model, the data is not\nused. You use labels that will be replaced by the real data only when the model\nis executed. \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\n\u2022\nDigital values or string of characters parameters can be entered directly as\nnumbers or chains, but they can also be choose among the entries of number or\nchain type.  \n\n\n\n<\/p>\n\n\n\n

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

    \u2022 The fields of an attribute table ( or another autonomous table) can be\nspecified by typing the field name or by using the table field entry . These\nfields will be choose when the model will be run . \n\n\u2022 Parent algorithms is an additional parameter available\nonly with the tools run from the graphic modeller . It allows you to define the\nexecution order of the algorithms . The definition of a parent algorithm forces\nthe modeller chart to be run before running the algorithm that owns this\nparent. Depending on the complexity of the model , you can have several\nbranches that come together or separate. The algorithms execution order will be\ndefined by QGis when running, but there is no guarantee that one algorithm be\nexecuted before another , EXCEPT if you use the option Parent<\/em><\/strong>Algorithm<\/em><\/strong>\n.\n\n\n\n<\/p>\n\n\n\n

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

    On the other side, if you have a linear model, without branches , when\nyou define an algorithm output of as an entry for the next you, automatically,\nset the first algorithm as a parent of the second . \n\nIn our example , we are going to execute as first\nalgorithm the calculation of a buffer zone around the oyster facilities.\n\n\n\n<\/p>\n\n\n\n

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

    It should be noted that instead of defining an explicit buffer distance,\nthe input buffer distance is used . Also, note that no output is named since\nthis output will be considered as an intermediate data set. \n\nTo complete our model , we will add the Clip tool\n(cutting) in the model\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\nWe\nwill use the following settings:
    \n\u2022 Input layer: Plots<\/em><\/strong>
    \n\u2022 Cutting layer : \u00ab\u00a0Buffer\u00a0\u00bb of the \u00ab\u00a0fixed distance buffer\u00a0\u00bb\nalgorithm
    \n\u2022 Output Layer (OutputVector): Riparian plots \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\nThe\nfinal model looks like the following screenshot.   \n\n\n\n<\/p>\n\n\n\n

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

    The connecting lines show how the elements are linked to each other in\nthe workflow. The inputs, outputs and algorithms are represented by different color\nboxes to distinguish them. The algorithms boxes contain also , on the left, an\nicon representing the source library . In our example , both algorithms are\nQGIS algorithms and have a Q<\/strong> icon in\nthe element box. <\/p>\n\n\n\n

    The model is now ready to be executed . <\/p>\n","protected":false},"excerpt":{"rendered":"

    The algorithms are added in   the graphic modeller as if they were data input. Simply select algorithms tab instead of Inputs data, to observe the corresponding display in the  Boxprocessingtool display. Once the algorithm to…<\/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_post_was_ever_published":false,"_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":""},"categories":[1260],"tags":[],"class_list":["post-8485","post","type-post","status-publish","format-standard","hentry","category-non-classe-en"],"aioseo_notices":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p6XU0A-2cR","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/8485","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=8485"}],"version-history":[{"count":0,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/posts\/8485\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/media?parent=8485"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/categories?post=8485"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sigterritoires.fr\/index.php\/wp-json\/wp\/v2\/tags?post=8485"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}