{"id":7335,"date":"2024-05-10T13:58:52","date_gmt":"2024-05-10T11:58:52","guid":{"rendered":"https:\/\/usemaps.com\/kb\/uncategorized\/simple-formulas\/"},"modified":"2024-05-10T13:58:52","modified_gmt":"2024-05-10T11:58:52","slug":"simple-formulas","status":"publish","type":"knowledgebase","link":"https:\/\/usemaps.com\/en\/usemaps-documentation\/definitions\/simple-formulas\/","title":{"rendered":"Simple Formulas"},"content":{"rendered":"

Simple Formulas are formulas that define automatic filling of attribute values. Attributes with a defined formula become locked for manual editing. The formula is recalculated every time the object is edited and also when the coordinate system of the data source is changed. <\/p>\n

Important:<\/strong><\/p>\n

    \n
  1. Simple Formulas can only be used for calculations within a single attribute. To automate calculations across multiple attributes and layers, Advanced Formulas should be used. <\/li>\n
  2. Before adding an attribute with a Simple Formula (a virtual attribute), make sure that the data source you are editing has the correct coordinate system.<\/li>\n
  3. How to change the coordinate system of a Data Source?<\/strong><\/li>\n
  4. The default coordinate system for newly created data sources in the web version of the System is Mercator (EPSG:3857). If you choose to stay in this coordinate system but still expect correct attribute values, such as segment length, it is important to either use a function that transforms coordinates to the application\u2019s coordinate system (appropriate for your location\u2019s coordinate system: PL-2000).<\/li>\n
  5. When creating virtual attributes, you should use the system field names, for example: nazwa_custom<\/code><\/li>\n<\/ol>\n

     <\/p>\n

    What is this used for?<\/strong><\/h4>\n

    This is a great tool when you need always up-to-date data for frequently edited objects, for example attributes like length, area, perimeter, or X and Y coordinates. A Simple Formula attribute can also be used for labeling layers, allowing this information to be included in prints. <\/p>\n

    Using Simple Formulas simplifies and supports daily analytical work or the creation of statistics. For numeric values, it is recommended to choose the attribute data type: real number. <\/p>\n

     <\/p>\n

    \"\"<\/a><\/p>\n

    Examples of formulas:<\/h4>\n
      \n
    • Combining values, i.e., concatenation of fields, for example Name and Description nazwa_custom || opis_custom<\/code><\/li>\n
    • Adding\/subtracting\/multiplying\/dividing the values of fields A and B: A + B<\/code>\/ A - B<\/code>\/ A * B<\/code>\/A \/ B<\/code><\/li>\n
    • Maximum\/minimum\/average\/sum of field A: MAX(A)<\/code>\/ MIN(A)<\/code> \/ AVG(A)<\/code> \/ SUM(A)<\/code><\/li>\n
    • ST_X(geom) \u2013 the formula returns the X coordinate of a point in the data source\u2019s coordinate system<\/li>\n
    • ST_Y(geom) \u2013 the formula returns the Y coordinate of a point in the data source\u2019s coordinate system<\/li>\n
    • ST_Y(ST_Transform(geom,4326)) \u2013 the formula returns the Y value \u2013 or X if changed to ST_X() \u2013<\/em> for a point in the EPSG:4326 (WGS84) coordinate system.<\/li>\n
    • ST_Length(geom) \u2013 the formula returns the length of the object in the units of the data source\u2019s coordinate system<\/li>\n
    • ST_Length(geom)::Numeric(10,2) \u2013 a variant of the above formula that returns the length in the coordinate system\u2019s units, rounded to two decimal places<\/li>\n
    • ST_Perimeter(geom) \u2013 a formula that returns the perimeter of a polygonal object, given in the units of the layer\u2019s coordinate system (usually meters)<\/span><\/li>\n
    • ST_Area(geom) \u2013 the formula returns the area of the object in the units of the coordinate system<\/li>\n
    • (ST_Area(geom)\/10000)::Numeric(10,4) \u2013 a variant of the above formula that returns the area in hectares, rounded to four decimal places, with the data type set as real number<\/li>\n
    • ‘https:\/\/openinframap.org\/#14.04\/’ || CAST(ST_Y(ST_centroid(ST_Transform(geom,4326))) AS varchar(20)) || ‘\/’ || CAST(ST_X(ST_centroid(ST_Transform(geom,4326))) AS varchar(20)) || ‘\/L,P,S’ \u2013 a formula that creates a link to the OpenInfrastructureMap portal, zooming to the centroid of the polygon.<\/code><\/li>\n<\/ul>\n

      What happens if, when trying to save an attribute using a Simple Formula, the System returns an \u201cinvalid content\u201d message to the user?<\/p>\n

      Due to the variety of user data sources and layers, we recommend that if you receive such a message, you first replace the term geom <\/em>in the formula with geometry<\/em>.<\/p>\n

       <\/p>\n","protected":false},"excerpt":{"rendered":"

      Simple Formulas are formulas that define automatic filling of attribute values. Attributes with a defined formula become locked for manual editing. The formula is recalculated every time the object is edited and also when the coordinate system of the data source is changed. Important: Simple Formulas can only be used for calculations within a single […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","template":"","knowledgebase_cat":[83],"knowledgebase_tag":[],"class_list":["post-7335","knowledgebase","type-knowledgebase","status-publish","hentry","knowledgebase_cat-definitions"],"_links":{"self":[{"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/knowledgebase\/7335","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/knowledgebase"}],"about":[{"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/types\/knowledgebase"}],"author":[{"embeddable":true,"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/comments?post=7335"}],"version-history":[{"count":0,"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/knowledgebase\/7335\/revisions"}],"wp:attachment":[{"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/media?parent=7335"}],"wp:term":[{"taxonomy":"knowledgebase_cat","embeddable":true,"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/knowledgebase_cat?post=7335"},{"taxonomy":"knowledgebase_tag","embeddable":true,"href":"https:\/\/usemaps.com\/en\/wp-json\/wp\/v2\/knowledgebase_tag?post=7335"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}