tune_areas()

static void tune_areas ( EFFECTIVE_AREAS *  ea, int  avoid_collaps, int  set_area, double  trshld  )

static

To get the effective area, we have to check what area a point results in when all smaller areas are eliminated.

Definition at line 234 of file effectivearea.c.

{
        LWDEBUG(2, "Entered  tune_areas");
        const double *P1;
        const double *P2;
        const double *P3;
        double area;
        int go_on=1;
        double check_order_min_area = 0;
 
        int npoints=ea->inpts->npoints;
        int i;
        int current, before_current, after_current;
 
        MINHEAP tree = initiate_minheap(npoints);
 
        int is3d = FLAGS_GET_Z(ea->inpts->flags);
 
 
        /*Add all keys (index in initial_arealist) into minheap array*/
        for (i=0;i<npoints;i++)
        {
                tree.key_array[i]=ea->initial_arealist+i;
                LWDEBUGF(2, "add nr %d, with area %lf, and %lf",i,ea->initial_arealist[i].area, tree.key_array[i]->area );
        }
        tree.usedSize=npoints;
 
        /*order the keys by area, small to big*/
        qsort(tree.key_array, npoints, sizeof(void*), cmpfunc);
 
        /*We have to put references to our tree in our point-list*/
        for (i=0;i<npoints;i++)
        {
                 ((areanode*) tree.key_array[i])->treeindex=i;
                LWDEBUGF(4,"Check ordering qsort gives, area=%lf and belong to point %d",((areanode*) tree.key_array[i])->area, tree.key_array[i]-ea->initial_arealist);
        }
        /*Ok, now we have a minHeap, just need to keep it*/
 
        /*for (i=0;i<npoints-1;i++)*/
        i=0;
        while (go_on)
        {
                /*Get a reference to the point with the currently smallest effective area*/
                current=minheap_pop(&tree, ea->initial_arealist)-ea->initial_arealist;
 
                /*We have found the smallest area. That is the resulting effective area for the "current" point*/
                if (i<npoints-avoid_collaps)
                        ea->res_arealist[current]=ea->initial_arealist[current].area;
                else
                        ea->res_arealist[current]=FLT_MAX;
 
                if(ea->res_arealist[current]<check_order_min_area)
                        lwerror("Oh no, this is a bug. For some reason the minHeap returned our points in the wrong order. Please file a ticket in PostGIS ticket system, or send a mial at the mailing list.Returned area = %lf, and last area = %lf",ea->res_arealist[current],check_order_min_area);
 
                check_order_min_area=ea->res_arealist[current];
 
                /*The found smallest area point is now regarded as eliminated and we have to recalculate the area the adjacent (ignoring earlier eliminated points) points gives*/
 
                /*FInd point before and after*/
                before_current=ea->initial_arealist[current].prev;
                after_current=ea->initial_arealist[current].next;
 
                P2= (double*)getPoint_internal(ea->inpts, before_current);
                P3= (double*)getPoint_internal(ea->inpts, after_current);
 
                /*Check if point before current point is the first in the point array. */
                if(before_current>0)
                {
 
                        P1= (double*)getPoint_internal(ea->inpts, ea->initial_arealist[before_current].prev);
                        if(is3d)
                                area=triarea3d(P1, P2, P3);
                        else
                                area=triarea2d(P1, P2, P3);
 
                        ea->initial_arealist[before_current].area = FP_MAX(area,ea->res_arealist[current]);
                        minheap_update(&tree, ea->initial_arealist, ea->initial_arealist[before_current].treeindex);
                }
                if(after_current<npoints-1)/*Check if point after current point is the last in the point array. */
                {
                        P1=P2;
                        P2=P3;
 
                        P3= (double*)getPoint_internal(ea->inpts, ea->initial_arealist[after_current].next);
 
 
                        if(is3d)
                                area=triarea3d(P1, P2, P3);
                        else
                                area=triarea2d(P1, P2, P3);
 
 
                        ea->initial_arealist[after_current].area = FP_MAX(area,ea->res_arealist[current]);
                        minheap_update(&tree, ea->initial_arealist, ea->initial_arealist[after_current].treeindex);
                }
 
                /*rearrange the nodes so the eliminated point will be ingored on the next run*/
                ea->initial_arealist[before_current].next = ea->initial_arealist[current].next;
                ea->initial_arealist[after_current].prev = ea->initial_arealist[current].prev;
 
                /*Check if we are finished*/
                if((!set_area && ea->res_arealist[current]>=trshld) || (ea->initial_arealist[0].next==(npoints-1)))
                        go_on=0;
 
                i++;
        };
        destroy_minheap(tree);
        return;
}

References areanode::area, area(), cmpfunc(), destroy_minheap(), POINTARRAY::flags, FLAGS_GET_Z, FP_MAX, getPoint_internal(), EFFECTIVE_AREAS::initial_arealist, initiate_minheap(), EFFECTIVE_AREAS::inpts, MINHEAP::key_array, LWDEBUG, LWDEBUGF, lwerror(), minheap_pop(), minheap_update(), areanode::next, POINTARRAY::npoints, areanode::prev, EFFECTIVE_AREAS::res_arealist, areanode::treeindex, triarea2d(), triarea3d(), and MINHEAP::usedSize.

Referenced by ptarray_calc_areas().

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