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« Create graph » Legend
Create graph |
This tool allow the qgis user to create a graphe from a polylines layer. It adds two fields called « i » and « j » in order to write starting and ending node ids. Node ids are create in texte format. The use of a prefix enables to paste an id with the incremental number automatically genrerated. For example, with the prefix ‘FR’ for France, nodes ids will be labelled FR1, FR2, ... The tool generates a node layer in the same CRS as the linear layer, which can be loaded automatically if the « Add nodes in active map » is checked
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« Create graph » Legend |
Invert |
This tool will revert the line direction of the previously selected polylines. |
Split |
This tool will split the previously selected polylignes into simple lines (only two points) |
Connect |
This tool allow to connect node layer objets to a linear objets layer. Each point will be connected to the nearest polyline, if the shortest distance to the polyline is lower than the serach radius The polyline will be split in two parts from each side of the connection point, in order to preserve the network topology NB : Multilinestringsare ignored |
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‘connect point’ legend |
Linear interpolation |
This tool enables the user to perform a deterministic linear-based interpolation to build cost grids, similarly as krieging generates. This methodology is based on acess time or cost varying along polylines and a radial spread from the closest segment. The methodology takes into account, direction of flow, side of spread and if the line is impassable or not. |
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Légende de l'image du dessus |
Parameters |
Parameters values of flow direction, side of spread and impassability must be coded as character of length 1 |
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Entête |
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Start node cost |
Access time or cost a the starting node of the polyline if the direction of travel is in the same direction of digitizing (From start to end) or Access time or cost a the ending node of the polyline if the direction of travel is in the opposite direction of digitizing (From end to start) |
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End node cost |
Access time or cost a the ending node of the polyline if the direction of travel is in the same direction of digitizing (From start to end) or Access time or cost a the starting node of the polyline if the direction of travel is in the opposite direction of digitizing (From end to start) |
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Flow direction |
‘0’ : prohibited link ‘1’ : one way link, in the same direction of digitizing ‘2’ : one way link, in the opposite direction of digitizing ‘3’ : two way link |
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Side of spread |
‘0’ : no spread allowed (highway, subway, cable car, …) excepted in stations ‘1’ : spread only on right side ‘2’ : spread only on left side ‘3’ : spread on both sides |
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Impassability |
‘0’ : passable link no restriction ‘1’ : impassability from left to right (not yet implemented) ‘2’ : impassability from right to left (not yet implemented) ‘3’ : impassability on both sides |
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Variable spread speed |
If checked, the spread speed is variying depending a layer field (to specify) , else it remains constant (spread speed field) |
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Pixel nb (x) |
The number of pixels in x dimension. It will update pixel size (x) |
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Pixel nb (Y) |
The number of pixels in y dimension. It will update pixel size (y) |
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Pixel size (x) |
The size of pixels in x dimension. It will update the number of pixels (x) |
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Pixel size (Y) |
The size of pixels in y dimension. It will update the number of pixels (y) |
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Decimals |
The number of decimals to approximate closetSegment distance. A too high value can cause dysfunctionning in case of superposed links (one way links in each direction) |
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Search radius |
The radius to search the nearest object from which to spread |
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Spread speed |
The speed of spread in case of constant spread speed |
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Taking into accound impassibility |
If checked, the tool wil take into accound impassable links (impassibility field in (1,2,3) |
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Add raster to current map |
If checked the generated grid will be add to canvas as a raster layer |
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Save raster as... |
To specify the name and the location of the generated grid |
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Isobands |
Limewise interpolation generates a raster based on access times or costs. In order to realize spatial analysis based on socioe-conomic data, it is necessary to generate isoband (polygon objects) to calculate for example the number of inhabitants livng in less than 30 minutes from the place to analyse
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Paramètre |
Band : Select the raster band you choose to analyse Min : Minimum value of isoband to generate Max : Minimum value of isoband to generate Step : Step between two isobandssiner. Save as : Specify the vector layer name of isobands Object type : « Polyline » for isolines or « Polygon » fri isobands. There wille be only one polyline or polygon per isoband value. |
