{"id":739,"date":"2016-10-10T22:33:12","date_gmt":"2016-10-10T20:33:12","guid":{"rendered":"http:\/\/hannes.enjoys.it\/blog\/?p=739"},"modified":"2016-10-11T19:23:45","modified_gmt":"2016-10-11T17:23:45","slug":"doing-things-to-the-whole-map-canvas-in-qgis","status":"publish","type":"post","link":"https:\/\/hannes.enjoys.it\/blog\/2016\/10\/doing-things-to-the-whole-map-canvas-in-qgis\/","title":{"rendered":"Doing things to the whole map canvas in QGIS"},"content":{"rendered":"

Due to a minor bug<\/a> in QGIS you need a very recent testing build. 2.16.3 is not recent enough but 2.16.4 would be.<\/strong><\/p><\/blockquote>\n

For cool tricks like vignetting or other eye candy, having a geometry that spans the whole map canvas in QGIS can be very useful.<\/p>\n

Using the @map_*<\/code> Variables available in expressions in combination with a Geometry generator style allows you to do this.<\/p>\n

@map_extent_center<\/code> returns a Point geometry of the current map canvas center, with x(@map_extent_center)<\/code> and y(@map_extent_center)<\/code> you get the x and y coordinates of it in the current CRS.
\n@map_extent_width<\/code> and @map_extent_height<\/code> return the width respectively height of the map canvas in CRS units.<\/p>\n

Our goal is to create a polygon that exactly matches the map canvas extents. Some simple math gets you there.<\/p>\n

First create Points for each of the corners by alternating the x+\/-width and y+\/-height. Then create a Line from all of them (the last point does not need to be the first again, make_polygon<\/code> does that for you). And use the line as outer ring for a Polygon.<\/p>\n

\r\nmake_polygon(\r\n make_line(\r\n  make_point(x(@map_extent_center)-@map_extent_width\/2, y(@map_extent_center)-@map_extent_height\/2),\r\n  make_point(x(@map_extent_center)+@map_extent_width\/2, y(@map_extent_center)-@map_extent_height\/2),\r\n  make_point(x(@map_extent_center)+@map_extent_width\/2, y(@map_extent_center)+@map_extent_height\/2),\r\n  make_point(x(@map_extent_center)-@map_extent_width\/2, y(@map_extent_center)+@map_extent_height\/2)\r\n )\r\n)\r\n<\/pre>\n
To actually see this, you need to use the style on a layer with at least one feature that is always visible where you want to focus your map canvas. Just make a polygon layer with one polygon that encloses the whole area. The layer must be in the same CRS as the project I think.<\/p>\n
You now have a Polygon that corresponds with the map canvas. Give it a radial gradient fill with some transparency and party!<\/p>\n
\"radialgradient\"
\n\"hh-bw\"
\n\"schiff-bw\"
\n\"stadion-bw\"
\n\"stadion-red\"<\/p>\n
All aerial images in the examples are <\/p>\n
Lizenz: Datenlizenz Deutschland Namensnennung 2.0
\nNamensnennung: Freie und Hansestadt Hamburg, Landesbetrieb Geoinformation und Vermessung
\nhttp:\/\/daten-hamburg.de\/geographie_geologie_geobasisdaten\/digitale_orthophotos\/DOP20\/DOP20_HH_fruehjahrsbefliegung_2015.zip<\/a><\/p><\/blockquote>\n
To make sure the feature you want to highlight is in the center, you could use another layer and @map_extent_center<\/code>.<\/p>\n
Yes, this totally is a hack but it’s fun!<\/p>\n","protected":false},"excerpt":{"rendered":"
Due to a minor bug in QGIS you need a very recent testing build. 2.16.3 is not recent enough but 2.16.4 would be. For cool tricks like vignetting or other eye candy, having a geometry that spans the whole map canvas in QGIS can be very useful. Using the @map_* Variables available in expressions in […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,29,31],"tags":[],"class_list":["post-739","post","type-post","status-publish","format-standard","hentry","category-cartography","category-gis","category-qgis"],"_links":{"self":[{"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/posts\/739","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/comments?post=739"}],"version-history":[{"count":11,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/posts\/739\/revisions"}],"predecessor-version":[{"id":756,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/posts\/739\/revisions\/756"}],"wp:attachment":[{"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/media?parent=739"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/categories?post=739"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hannes.enjoys.it\/blog\/wp-json\/wp\/v2\/tags?post=739"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}