Dieses Problem gelöst werden kann, die Priority-Flood-Algorithmus. Es ist schon einige Male in den letzten Jahrzehnten (und wieder von anderen Menschen diese Frage zu beantworten) entdeckt und veröffentlicht, obwohl die spezifische Variante Sie suchen ist nicht, mein Wissen in der Literatur.
Sie können eine Übersichtsarbeit des Algorithmus und seine Varianten here finden. Seitdem dieses Papier veröffentlicht wurde, wurde eine noch schnellere Variante entdeckt (link), sowie Verfahren, um diese Berechnung an Datensätzen von Billionen von Zellen durchzuführen (link). Ein Verfahren zum selektiven Durchbrechen niedriger/enger Teilungen wird diskutiert here. Kontaktieren Sie mich, wenn Sie Kopien von diesen Papieren wünschen.
Ich habe ein Repository here mit vielen der oben genannten Varianten; Weitere Implementierungen finden Sie unter here.
Ein einfaches Skript Volumen berechnen die RichDEM Bibliothek ist wie folgt:
#include "richdem/common/version.hpp"
#include "richdem/common/router.hpp"
#include "richdem/depressions/Lindsay2016.hpp"
#include "richdem/common/Array2D.hpp"
/**
@brief Calculates the volume of depressions in a DEM
@author Richard Barnes ([email protected])
Priority-Flood starts on the edges of the DEM and then works its way inwards
using a priority queue to determine the lowest cell which has a path to the
edge. The neighbours of this cell are added to the priority queue if they
are higher. If they are lower, then they are members of a depression and the
elevation of the flooding minus the elevation of the DEM times the cell area
is the flooded volume of the cell. The cell is flooded, total volume
tracked, and the neighbors are then added to a "depressions" queue which is
used to flood depressions. Cells which are higher than a depression being
filled are added to the priority queue. In this way, depressions are filled
without incurring the expense of the priority queue.
@param[in,out] &elevations A grid of cell elevations
@pre
1. **elevations** contains the elevations of every cell or a value _NoData_
for cells not part of the DEM. Note that the _NoData_ value is assumed to
be a negative number less than any actual data value.
@return
Returns the total volume of the flooded depressions.
@correctness
The correctness of this command is determined by inspection. (TODO)
*/
template <class elev_t>
double improved_priority_flood_volume(const Array2D<elev_t> &elevations){
GridCellZ_pq<elev_t> open;
std::queue<GridCellZ<elev_t> > pit;
uint64_t processed_cells = 0;
uint64_t pitc = 0;
ProgressBar progress;
std::cerr<<"\nPriority-Flood (Improved) Volume"<<std::endl;
std::cerr<<"\nC Barnes, R., Lehman, C., Mulla, D., 2014. Priority-flood: An optimal depression-filling and watershed-labeling algorithm for digital elevation models. Computers & Geosciences 62, 117–127. doi:10.1016/j.cageo.2013.04.024"<<std::endl;
std::cerr<<"p Setting up boolean flood array matrix..."<<std::endl;
//Used to keep track of which cells have already been considered
Array2D<int8_t> closed(elevations.width(),elevations.height(),false);
std::cerr<<"The priority queue will require approximately "
<<(elevations.width()*2+elevations.height()*2)*((long)sizeof(GridCellZ<elev_t>))/1024/1024
<<"MB of RAM."
<<std::endl;
std::cerr<<"p Adding cells to the priority queue..."<<std::endl;
//Add all cells on the edge of the DEM to the priority queue
for(int x=0;x<elevations.width();x++){
open.emplace(x,0,elevations(x,0));
open.emplace(x,elevations.height()-1,elevations(x,elevations.height()-1));
closed(x,0)=true;
closed(x,elevations.height()-1)=true;
}
for(int y=1;y<elevations.height()-1;y++){
open.emplace(0,y,elevations(0,y) );
open.emplace(elevations.width()-1,y,elevations(elevations.width()-1,y));
closed(0,y)=true;
closed(elevations.width()-1,y)=true;
}
double volume = 0;
std::cerr<<"p Performing the improved Priority-Flood..."<<std::endl;
progress.start(elevations.size());
while(open.size()>0 || pit.size()>0){
GridCellZ<elev_t> c;
if(pit.size()>0){
c=pit.front();
pit.pop();
} else {
c=open.top();
open.pop();
}
processed_cells++;
for(int n=1;n<=8;n++){
int nx=c.x+dx[n];
int ny=c.y+dy[n];
if(!elevations.inGrid(nx,ny)) continue;
if(closed(nx,ny))
continue;
closed(nx,ny)=true;
if(elevations(nx,ny)<=c.z){
if(elevations(nx,ny)<c.z){
++pitc;
volume += (c.z-elevations(nx,ny))*std::abs(elevations.getCellArea());
}
pit.emplace(nx,ny,c.z);
} else
open.emplace(nx,ny,elevations(nx,ny));
}
progress.update(processed_cells);
}
std::cerr<<"t Succeeded in "<<std::fixed<<std::setprecision(1)<<progress.stop()<<" s"<<std::endl;
std::cerr<<"m Cells processed = "<<processed_cells<<std::endl;
std::cerr<<"m Cells in pits = " <<pitc <<std::endl;
return volume;
}
template<class T>
int PerformAlgorithm(std::string analysis, Array2D<T> elevations){
elevations.loadData();
std::cout<<"Volume: "<<improved_priority_flood_volume(elevations)<<std::endl;
return 0;
}
int main(int argc, char **argv){
std::string analysis = PrintRichdemHeader(argc,argv);
if(argc!=2){
std::cerr<<argv[0]<<" <Input>"<<std::endl;
return -1;
}
return PerformAlgorithm(argv[1],analysis);
}
Es sollte geradlinig sein, dies zu Format, was auch immer 2d Array anzupassen sind Sie
In Pseudo-Code verwenden, die findet auf den vorhergehenden äquivalent:
Let PQ be a priority-queue which always pops the cell of lowest elevation
Let Closed be a boolean array initially set to False
Let Volume = 0
Add all the border cells to PQ.
For each border cell, set the cell's entry in Closed to True.
While PQ is not empty:
Select the top cell from PQ, call it C.
Pop the top cell from PQ.
For each neighbor N of C:
If Closed(N):
Continue
If Elevation(N)<Elevation(C):
Volume += (Elevation(C)-Elevation(N))*Area
Add N to PQ, but with Elevation(C)
Else:
Add N to PQ with Elevation(N)
Set Closed(N)=True
Es ist derselbe Algorithmus, der zur Berechnung der Fraktur in Metallen verwendet wurde. –
Diese Frage ist wohl auch im Zusammenhang mit: http://stackoverflow.com/questions/15033555/tips-on-finding-the-volume-of-water-in-a-3d-chess-board/ – user3838351