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7

It is very difficult to know exactly where things went wrong without knowing details about the inputs that you used for each tool. However looking at the two images that you embedded into your post, it looks to me like the common problem of running a flow path analysis on a non-hydrologically preprocessed DEM, i.e. a DEM for which you have removed all of the ...


6

If your vectors are not necessarily in the right direction and if you have a point shapefile with elevations and correct topology, I would suggest the following: Create a 'WKT' field in your point data with the WKT geometry of your point, using the field calculator: geom_to_wkt( $geometry) ; For your pipe layer, choose expression-based rotation for your ...


6

I know ArcGIS's python interpreter is weird, but I'm pretty sure your syntax is wrong. My recollection is that you don't need to use their weird escape characters within the scope of the function definition. So your code would become: def reclass(grid_value): if (grid_value == 64): return 0 elif (grid_value == 128): return 45 ...


5

I don't believe that GDAL currently offers the functionality needed to perform flow path modelling and automated stream network extraction. There are however many good open-source GIS alternatives that can be used for this task. I know that GRASS, SAGA, and QGIS each have tools for flow accumulation and stream network extraction. Also, I develop a free and ...


5

I can think of a few ways to do this: Symbolize the lines so they have direction indicated, and manually Flip those in the wrong direction. Use an attribute if available or a calculation (such as end z > start z) to select segments going the wrong direction and Flip (GP) them. Create a geometric network of the lines and use the Flow Direction tools, setting ...


5

Mostly this is a matter of implementation. They have not been implemented. Typically, each tool was historically developed in for a specific project or purpose and this development process has not resulted in complete consistency in the functionality available. I think all the algorithms would make sense with D8 too. Two of the tools (DinfAvalanche, ...


4

The flow direction is indeed an 8 bit image, irrespective of your input (32 or 64 bit float), from the Esri help page: From the centre pixel (blue) the value indicates which way the flow will go from 1 (East) to 128 (Northeast).. From flow direction you need to proceed to Flow Accumulation or Flow Length which uses this direction raster to calculate the ...


4

To my knowledge there is no tool that can do what you are asking, this needs to be done in a programmatic way. If you have VBA installed and licensed then the following code will select indeterminate edges. It assumes the geometric network is the first layer in your TOC and you need to edit the line to update it with the name of your featuredataset (current ...


4

It is called Lake Flood. I recommend SAGA GUI, but if it has to be done in QGIS, you can find it in the Processing Toolbox | SAGA | Terrain Analysis - Hydrology | Lake flood. Your manhole points has to be rasterized to be a Seeds raster beforehand. Please make sure the dimension (cell size, extent) of the Seeds raster is the same as your DEM. Lake Flood ...


4

You could do a join between the three layers, then aggregate by layerB. Virtual layers can likely be used. I am not sure if the important data is in layerA or in the flow layer.. Here is an (untested) possibility: SELECT b.id, b.geometry, sum(a.myVar) FROM layerB b LEFT JOIN flow f ON ST_Intersects(ST_EndPoint(f.geometry),b.geometry) JOIN layerA a ON ...


4

With the Virtual Layers, theoretically, it's possible (with shapefiles, the process will be extra long, but if the layers are in a Spatial Database, I think it is a lot faster). Here the code : WITH inter_ab AS ( --create intersection between LayerA and LayerB SELECT LayerA.id || '_' || LayerB.FLAECHEID AS id, LayerA.id AS id_a, ST_AREA(LayerA.geometry)...


3

I solved this problem by converting the cells under the stream network to 'NO DATA' as per FelixIP's comment and recalculating the flow length. I set the stream network cells to NO DATA using the Raster Calc equation: SetNull(~(IsNull("Stream Raster")), "Original Flow Direction Raster") Also of note, when calculating flow length, must set as DOWNSTREAM ...


3

There's a QGIS plugin Switch the Direction of a Polyline that does exactly what it says. Install it, and you get an additional button on your plugin toolbar that looks like a plug. With your pipe polyline layer in editing mode, select the features that you want to reverse the direction of, and click the button.


3

When working with Geometric networks I find it is best to specify either a source or a sink not both. Here is Esri help section on this topic In utility network applications, knowing the direction of flow along network edges can be essential. The commodity that flows through the network—water, electricity, and oil—has no will of its own. The network ...


3

Here is a rambling set of resources/publications I have collected on the topic. Ratti, Carlo, Stanislav Sobolevsky, Francesco Calabrese, Clio Andris, Jonathan Reades, Mauro Martino, Rob Claxton & Steven H. Strogatz. (2010) Redrawing the map of Great Britain from a Network of Human Interactions. PLoS ONE 5(12). Article is open access from link. Flow ...


3

You already figured out your problem. The unit of measure is in degrees, therefore your raster is a measure of flow length in degrees. Before doing your analysis, you need to use the Project tool to re-project your data into a projected coordinate system so that it uses a linear unit. If you have not worked with projections much, be sure to use the ...


3

Using your raster and the default input parameters: it gives me a raster with only nanvalues (I think because I'm requesting something from an additional input layer that is not specified): Instead, unchecking the Seeds only option, it seems to work: but I don't know what this output means and if it is a correct result.


3

Regarding your first question (it's usually better to focus on one question per post): In GRASS you can display vectors with direction arrows. In the gui there's a checkbox "Display direction of linear features". So if you have run r.watershed, then you probably have created a raster stream network. With two addition commands you can convert this to a ...


3

I would recommend the Indicator Kriging approach as well. Using indicator kriging to produce a probability or standard error of indicators map assumes an unknown constant mean. In addition, Indicator kriging can use either semivariograms or covariances, which are the mathematical forms you use to express autocorrelation. The observed binary data is given ...


3

Although it's not a tool within QGIS, I've used Gephi for something similar: https://gephi.org/ You can use it to represent your data as a number of nodes with relationships in a graph, which seems like what you're after. I used it to visualise commuting patterns between cities.


3

You can use this expression, details in comments : -- create a start point variable with_variable( 'start_point', -- name make_point("Origin Longitude", "Origin Latitude"), -- expression for start point -- create an end point variable with_variable( 'end_point', -- name make_point("Dest Longitude", "Dest Latitude"), -- expression for end ...


2

In Wilson et al. 2008 (http://spatial.usc.edu/wp-content/uploads/Water-in-the-Landscape.pdf) "The FD8 multiple flow direction (MFD) algorithm developed by Quinn et al. (1991) directs water to every adjacent downslope cell on a slope- weighted basis." p. 217.


2

I made a simmilar application a few time ago. I registered my cellphone position, sending a CSV each 5 minutes, and inserting it in a postGIS database. To sum up: Load csv in PostGIS database. I made it with shell script in the server, run each 5 minutes, and update the table. Filter the results on the database. Once in postgis, you can export it to a kml/...


2

One of the easier ways to do this is with a spatial database such as PostGIS. Load your raster into the database using raster2pgsql (which is installed with PostGIS) and then load your rivers with shp2pgsql (also installed with PostGIS). Then, you can run a simple query that samples the elevation model at the end points of all your lines: select ...


2

By just changing the symbology you can inspect the results visually, nothing else. By doing that you simply set a flow accumulation threshold what you want to see. This of course depends on the case and there are no exact answers what is right amount of flow accumulation for channel initialization. This visualization trick is of course very useful to ...


2

With Network Analyst, using the Location Allocation tool. Input your origins as facilities, and destinations as demand points. This should give you a result of associated points, which then can be used to create polygons using either Feature to Polygon or Construct Polygon, Help Site


2

The method that you used for 'excluding' data only applies to the symbology. So you are not really modifying the data, just what you see. I would create a new raster that removes the data from the waterbodies. More than one way to go about this. It also depends on your area of interest. You could use the Set Null tool to remove the values of the water ...


2

GRASS numbers the directions in a drainage (flow direction) raster from 1-8 starting eastward and going counter clock-wise. What about the negative numbers? GRASS uses negative direction to indicate that the flow from this cell is going off the map. But the absolute value still indicates the direction. So both 4 and -4 mean west. Also, GRASS uses 0 to ...


2

You need to create a hydrologically corrected (depressionless) DEM from your contours through interpolation to a raster DEM. Then you need to perform a flow accumulation operation, such that the pipes serve as the seed points and the downslope flowpaths issuing from these locations are traced. Many GIS have specific tools to perform this type of flowpath ...


2

Note this may need QGIS 2.14, recently released. Turn your data into Line features with two points, in the order of origin, destination. Every feature must be a Line with two points only. Open the attribute table, enable editing, and add a new attribute that is a Decimal Number with Length 8 and precision 2. Name it "angle". Now we're going to set that ...


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