I want to access node coordinate in cmesh #780

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1. jmark commented on Oct 5, 2023

   

   jmark

   on Oct 5, 2023

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   Hello @syusaku625,

   I recommend to check out this tutorial https://github.com/DLR-AMR/t8code/wiki/Step-6-Computing-stencils and associated source code https://github.com/DLR-AMR/t8code/blob/main/tutorials/general/t8_step6_stencil.cxx .

   This shows how to access information like volume, centroid, etc per element. For node coordinates there are the following functions:

   /** Compute the coordinates of a given vertex of an element if a geometry
    * for this tree is registered in the forest's cmesh.
    * \param [in]      forest     The forest.
    * \param [in]      ltree_id   The forest local id of the tree in which the element is.
    * \param [in]      element    The element.
    * \param [in]      corner_number The corner number, in Z-order, of the vertex which should be computed.
    * \param [out]     coordinates On input an allocated array to store 3 doubles, on output
    *                             the x, y and z coordinates of the vertex.
    */
   void
   t8_forest_element_coordinate (t8_forest_t forest, t8_locidx_t ltree_id, const t8_element_t *element, int corner_number,
                                 double *coordinates);
   
   /** Compute the coordinates of a point inside an element inside a tree.
    *  The point is given in reference coordinates inside the element and gets
    *  converted to reference coordinates inside the tree. After that, the point
    *  is converted to global coordinates inside the domain. If needed, the element
    *  is stretched by the given stretch factors (the resulting mesh is then 
    *  no longer non-overlapping).
    * 
    * \param [in]      forest            The forest.
    * \param [in]      ltreeid           The forest local id of the tree in which the element is.
    * \param [in]      element           The element.
    * \param [in]      ref_coord         The reference coordinates of the point inside the element.
    * \param [in]      num_coords        The number of coordinate sets in ref_coord (dimension x double).
    * \param [out]     coords_out        On input an allocated array to store 3 doubles, on output
    *                                    the x, y and z coordinates of the point inside the domain.
    * \param [in]      stretch_factors   An element-wise array with d (dimension) doubles per element, 
    *                                    which are used to stretch the element beyond its original boundary.
    *                                    The array must be of length forest->local_num_elements * d.
    *                                    If NULL, no stretching is applied.
    */
   void
   t8_forest_element_from_ref_coords (t8_forest_t forest, t8_locidx_t ltreeid, const t8_element_t *element,
                                      const double *ref_coord, const size_t num_coords, double *coords_out,
                                      sc_array_t *stretch_factors);
   

   If you are only interested in node coordinates on cmesh level then I suggest to initialize a uniform forest on your cmesh with level set to 0.

   Does this answer your question?
2. DLR-AMR

   locked and limited conversation to collaborators on Oct 5, 2023
3. jmark

   converted this issue into a discussion #781 on Oct 5, 2023