grid_graph vertex properties

[David Doria]

Since there is no VertexProperties template parameter on grid_graph,
is it correct that you cannot use interior properties, but must use
exterior properties?

Thanks,

David

[Jeremiah Willcock]

Post by David Doria
Since there is no VertexProperties template parameter on grid_graph,
is it correct that you cannot use interior properties, but must use
exterior properties?

Yes, that is correct. Both vertex and edge index maps exist, though, so
it is easy to use external properties for both of those (unlike edge
properties for adjacency_list).

-- Jeremiah Willcock

[David Doria]

Yes, that is correct.  Both vertex and edge index maps exist, though, so it
is easy to use external properties for both of those (unlike edge properties
for adjacency_list).

Hm, I've been playing with this for a while now and I don't seem to
understand how to add something to the vertex index map.

This compiles, but I think it is creating a new map:

#include <iostream>
#include <boost/array.hpp>
#include <boost/graph/grid_graph.hpp>

int main(int argc, char* argv[])
{
typedef boost::grid_graph<2> GraphType;

const unsigned int dimension = 5;
boost::array<std::size_t, 2> lengths = { { dimension, dimension } };
GraphType graph(lengths);

boost::graph_traits<GraphType>::vertex_descriptor v = { { 0, 1 } };

std::vector<float> vertexData(dimension * dimension, 0);

boost::grid_graph_index_map<GraphType,
boost::graph_traits<GraphType>::vertex_descriptor, float>
myMap(graph);

float retrieved = get(myMap, v);
std::cout << "Retrieved: " << retrieved << std::endl;

}

Could you demonstrate how to do this? We should really add this to the
grid_graph documentation :)

Thanks,

David

[Jeremiah Willcock]

Post by David Doria

Yes, that is correct.  Both vertex and edge index maps exist, though, so it
is easy to use external properties for both of those (unlike edge properties
for adjacency_list).

Hm, I've been playing with this for a while now and I don't seem to
understand how to add something to the vertex index map.
#include <iostream>
#include <boost/array.hpp>
#include <boost/graph/grid_graph.hpp>
int main(int argc, char* argv[])
{
typedef boost::grid_graph<2> GraphType;
const unsigned int dimension = 5;
boost::array<std::size_t, 2> lengths = { { dimension, dimension } };
GraphType graph(lengths);
boost::graph_traits<GraphType>::vertex_descriptor v = { { 0, 1 } };
std::vector<float> vertexData(dimension * dimension, 0);
boost::grid_graph_index_map<GraphType,
boost::graph_traits<GraphType>::vertex_descriptor, float>
myMap(graph);

This should just be (something like):

typedef boost::property_map<GraphType, boost::vertex_index_t>::const_type
indexMapType;

indexMapType indexMap(get(boost::vertex_index, graph));

boost::iterator_property_map<std::vector<float>::iterator, indexMapType>
myMap(vertexData.begin(), indexMap);

// grid_graph_index_map is internal

Post by David Doria
float retrieved = get(myMap, v);
std::cout << "Retrieved: " << retrieved << std::endl;
}
Could you demonstrate how to do this? We should really add this to the
grid_graph documentation :)

-- Jeremiah Willcock

[David Doria]

Post by Jeremiah Willcock
typedef boost::property_map<GraphType, boost::vertex_index_t>::const_type
indexMapType;
indexMapType indexMap(get(boost::vertex_index, graph));
boost::iterator_property_map<std::vector<float>::iterator, indexMapType>
myMap(vertexData.begin(), indexMap);
// grid_graph_index_map is internal

Thanks, that seems to do it.

For posterity:
http://programmingexamples.net/wiki/CPP/Boost/BGL/GridGraphProperties

David

[Jeremiah Willcock]

Post by David Doria

Post by Jeremiah Willcock
typedef boost::property_map<GraphType, boost::vertex_index_t>::const_type
indexMapType;
indexMapType indexMap(get(boost::vertex_index, graph));
boost::iterator_property_map<std::vector<float>::iterator, indexMapType>
myMap(vertexData.begin(), indexMap);
// grid_graph_index_map is internal

Thanks, that seems to do it.
http://programmingexamples.net/wiki/CPP/Boost/BGL/GridGraphProperties

For future reference, that is the approach to build external property maps
for all types of graphs, not just grid graphs.

-- Jeremiah Willcock