{"id":9774,"date":"2023-04-16T22:00:15","date_gmt":"2023-04-16T20:00:15","guid":{"rendered":"https:\/\/www.sigterritoires.fr\/?p=9774"},"modified":"2023-04-17T15:39:05","modified_gmt":"2023-04-17T13:39:05","slug":"s57-charts-with-qgis-display-soundings","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/s57-charts-with-qgis-display-soundings\/","title":{"rendered":"S57 Charts with QGis: display soundings"},"content":{"rendered":"\n

In a previous article<\/a> we discussed how to display a symbology appropriate to S57 files. In this article we did not discuss how to display the values of bathimetric soundings for two reasons: the first because the soundings themselves have no symbology. They are represented by labels, not symbols. The second because they require special treatment to be displayed.<\/p>\n\n\n\n\n\n\n\n

The S57 sounding layer<\/h2>\n\n\n\n

The soundings are contained in the SOUNDG layer.<\/p>\n\n\n\n

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

But once the attribute table is opened, there is no attribute that looks like the value of a sounding.<\/p>\n\n\n\n

The information to find them is at the level of the layer type:<\/p>\n\n\n\n

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

This layer is not a geographic xy layer but an xyz layer. It is the Z of the geometry that contains the value of the sounding and not an attribute of the attribute table.<\/p>\n\n\n\n

To be able to use it as a sounding point label, you must create an attribute and recover the Z value of the geometry.<\/p>\n\n\n\n

But before doing so, another point must be made: SOUNDG is a multipoint type layer. If we want to recover the value of all points and not just the first point of the multipoints, we need to transform the layer into a simple geometry type.<\/p>\n\n\n\n

From multipointZ to pointZ<\/h2>\n\n\n\n
\"\"<\/a><\/figure>\n\n\n\n

To change the geometry type, we use the \u00ab De morceaux multiples \u00e0 morceaux uniques<\/em><\/strong> \u00bbtreatment of the \u201cVector Geometry\u201d toolbox.<\/p>\n\n\n\n

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

On this new PointZ layer we can now retrieve the sounding values.<\/p>\n\n\n\n

Retrieving Sounding Values<\/h2>\n\n\n\n

We open the attribute table and the field calculator:<\/p>\n\n\n\n

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

We define a new integer field and assign it the z($geometry)\/10<\/strong> expression that retrieves the Z value of the geometry. The division by 10 is necessary because the S57 sounding values are not in meters but in decimetres.<\/p>\n\n\n\n

We then have an attribute with sounding values that can be used to generate labels on the chart.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n
\n
\"\"<\/a><\/figure>\n<\/div>","protected":false},"excerpt":{"rendered":"

In a previous article we discussed how to display a symbology appropriate to S57 files. In this article we did not discuss how to display the values of bathimetric soundings for two reasons: the first because…<\/p>\n","protected":false},"author":1,"featured_media":9781,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_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,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[1260],"tags":[],"class_list":["post-9774","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-non-classe-en"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t