[gdal-dev] creating graph for single line shape layer using gdal gnm
yhema
hema.yeedunuri at amigooptima.in
Wed Nov 12 02:28:19 PST 2014
hello Mikhail Gusev ,
Is it correct to do this way?First I will save point layer using start and
end points of line layer.Again then connect the two layers using
autoconnect method . So that I can find shortest path between features of
the line layer.
thanks,
hema
On Wed, Nov 12, 2014 at 3:03 PM, Михаил Гусев [via OSGeo.org] <
ml-node+s1560n5172509h97 at n6.nabble.com> wrote:
> The algorithm is using only the features that are connected manually and
>> that are present in _gnm_graph.
>
>
> No, if you use automatic connection the _gnm_graph is also formed
> automatically because it internally calls ConnectFeatures().
>
> Is there any other simple solution to solve this.
>>
>
> It is no other solution for now to solve this. I think in the nearest
> future the new algorithm of automatic connection can be written (which
> regards only line layers and determines the start and end point of the
> lines automatically), I'm working on this now.
>
> 2014-11-11 14:48 GMT+04:00 Hema Yeedunuri <[hidden email]
> <http://user/SendEmail.jtp?type=node&node=5172509&i=0>>:
>
>> hello Mikhail Gusev ,
>>
>> Thank u for the reply .I want to find the shortest distance between
>> features .But the road layer I am using is having 10055 features. without
>> creating graph it is not possible to find shortest distance.And to my
>> understanding I think it is difficult to manually connect features to
>> create graph. The algorithm is using only the features that are connected
>> manually and that are present in _gnm_graph.dbf file.Is there any other
>> simple solution to solve this.
>>
>> thanks,
>> hema
>>
>> On Tue, Nov 11, 2014 at 3:59 PM, Mikhail Gusev <[hidden email]
>> <http://user/SendEmail.jtp?type=node&node=5172509&i=1>> wrote:
>>
>>> Hello, hema.
>>> The current default implementation of GNMNetwork::AutoConnect() can work
>>> only if the passing array of layers contains at least one point and one
>>> line layer (i.e. GetGeomType() for the layers equals wkbPoint and
>>> wkbLineString accordingly). For each line feature the algorithm takes the
>>> start and end snapping area formed around the start and end point of the
>>> line and searches the points from point layers which are situated inside
>>> these two areas. So there is no way for now to connect features of only one
>>> line layer automatically. You can use ConnectFeatures() to connect
>>> manually, but you will need the features (with any geometry!) to be the
>>> source and the target for the connection, while the gnm_roads_line feature
>>> will be the connector.
>>>
>>> 2014-11-11 11:26 GMT+04:00 yhema <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=5172509&i=2>>:
>>>
>>>> Hello all,
>>>>
>>>> I am trying to create a graph for network analysis using gdalgnm.The
>>>> feature
>>>> auto connect is working if we provide more than one layer.How can we
>>>> connect
>>>> features of a single layer so that graph is created automatically. We
>>>> can
>>>> connect features using connect features but automatically it is not
>>>> conncting using auto connect .Here is the code.
>>>>
>>>> char **options = NULL;
>>>> options = CSLAddNameValue(options,GNM_INIT_OPTIONPAIR_NAME,
>>>> "roads_network");
>>>>
>>>>
>>>> GNMGdalNetwork *poNet;
>>>>
>>>> poNet =
>>>>
>>>> GNMManager::GdalCreateNetwork("/home/shiva/Desktop/network/network_data",
>>>> "ESRI Shapefile", "EPSG:4326", options);
>>>> CSLDestroy(options);
>>>> if (poNet == NULL)
>>>> {
>>>> printf("Failed to create network\n");
>>>> exit(1);
>>>> }
>>>>
>>>> GDALDataset *poSrcDS = (GDALDataset*)
>>>> GDALOpenEx("/home/shiva/Desktop/network/data",
>>>> GDAL_OF_VECTOR |
>>>> GDAL_OF_READONLY, NULL, NULL, NULL );
>>>> if(poSrcDS == NULL)
>>>> {
>>>> printf("Can not open source dataset at\n");
>>>> exit(1);
>>>> }
>>>>
>>>> OGRLayer *poSrcLayer2 = poSrcDS->GetLayerByName("roads");
>>>> if (poSrcLayer2 == NULL)
>>>> {
>>>> printf("layer is null\n");
>>>> printf("Can not process layers of source dataset\n");
>>>> exit(1);
>>>> }
>>>>
>>>> GNMErr err2 = poNet->CopyLayer(poSrcLayer2, "roads");
>>>> if (err2 != GNMERR_NONE)
>>>> {
>>>> printf("Can not import layers from source dataset\n");
>>>> exit(1);
>>>> }
>>>>
>>>> GDALClose(poSrcDS);
>>>>
>>>>
>>>> if (poNet->CreateRule("CLASS gnm_roads_line COSTS TIGER_ID") !=
>>>> GNMERR_NONE)
>>>> {
>>>> printf("Can not create rule\n");
>>>> }
>>>>
>>>> if (poNet->CreateRule("NETWORK CONNECTS gnm_roads_line WITH
>>>> gnm_roads_line ") != GNMERR_NONE)
>>>> {
>>>> printf("Can not create rule\n");
>>>> }
>>>>
>>>>
>>>> printf("\nBuilding network topology ...\n");
>>>> GDALDataset *poNetDS = poNet->GetDataset();
>>>> OGRLayer **layers = new OGRLayer*[3];
>>>>
>>>> layers[0] = poNetDS->GetLayerByName("gnm_roads_line");
>>>> layers[2] = NULL;
>>>> layers[1] = NULL;
>>>>
>>>>
>>>> if (poNet->AutoConnect(layers,0.05, NULL) != GNMERR_NONE)
>>>> {
>>>> printf("Building topology failed\n");
>>>> exit(1);
>>>> }
>>>> else
>>>> {
>>>> printf("Topology has been built successfully\n");
>>>> }
>>>>
>>>> delete[] layers;
>>>>
>>>>
>>>> GNMManager::GdalCloseNetwork(poNet);
>>>>
>>>>
>>>>
>>>>
>>>> thanks,
>>>> hema
>>>>
>>>>
>>>>
>>>> --
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>>>
>>>
>>
>
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