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7 votes

Calculate flow path with QGIS

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, ...
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6 votes

Displaying arrows on pipes from upstream to downstream using QGIS?

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 ...
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  • 1,802
6 votes
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Why TauDEM specialized tools (e.g. D-Infinity Distance Down) are only available with D-Infinity flow model?

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 ...
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6 votes

Getting angle of point generated from DEM in Raster using Field Calculator in ArcGIS Desktop?

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 ...
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  • 840
5 votes

How to extract drainage network through gdaldem

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 ...
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  • 10.8k
5 votes
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How to assign correct flow direction to stream network polylines?

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 ...
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  • 15.5k
5 votes
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Transferring flows (connections and values) between polygons in QGIS

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 : -- ...
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  • 11.8k
5 votes
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Arrow head at the last path segment of Bezier curve

Try geometry generator with: make_line(point_n( $geometry, -2), end_point($geometry)) The second last point and last/end point is used to create a line:
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4 votes
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ArcGIS Geometric Network - Identify Indeterminate Flow

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 ...
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4 votes
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flow direction and flow length in arcmap

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 ...
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4 votes

Showing overland flow route on DEM in QGIS?

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 ...
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  • 29k
4 votes

Transferring flows (connections and values) between polygons in QGIS

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) ...
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3 votes
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Flow Path length

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, ...
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  • 15.5k
3 votes

Incorrect length from Flow Length tool

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 ...
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  • 986
3 votes

Calculating flowpath length to stream within catchment using ArcGIS Desktop?

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 ...
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  • 61
3 votes
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How to display Flow Direction arrows + Burn Stream Netwok in QGIS?

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 ...
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3 votes

Interpolation of river pollution data

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 ...
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  • 11.8k
3 votes

How to extract a flow chart from points connected with lines?

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 ...
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  • 2,486
3 votes
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Generating slightly curved arrows in QGIS 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 ...
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  • 11.8k
2 votes
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Exporting massive gps tracks to a map

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 ...
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  • 1,033
2 votes
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Flow direction and catchment area polygons for utility water pipes

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 ...
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  • 10.8k
2 votes

How to extract elevation values at line start and end points from a DEM?

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 ...
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  • 3,041
2 votes

Understanding flow accumulation

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 ...
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  • 618
2 votes
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Defining area of influence for origin-destination dataset (where destination is port) using ArcGIS for Desktop?

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 ...
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  • 6,876
2 votes
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Problem with flow lines in ArcMap

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 ...
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  • 1,344
2 votes

Color gradient to show direction in polygons (filling, color ramp, gradients)

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 ...
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  • 51.1k
2 votes
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What are the meaning of Grass drainage direction values from r.watershed

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 ...
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  • 1,761
2 votes

Understanding hydrology and DEM results?

To understand why, have a look at your flow direction raster. In a flat filled area such as this, the flow direction is limited to the flat filled surface regardless of whatever topography may have ...
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  • 1,292
2 votes

Fast, simple assignment of flow directions to flats in GRASS

r.watershed doesn't require filling depressions, because it uses least cost path for routing. Try -b flag (Flow direction in flat areas is modified to look prettier).
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  • 721
2 votes
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Longest flow path in QGIS from single feature vector

There is a tool in Whitebox Geospatial Analysis Tools called Vector Stream Network Analysis within the Stream Network Analysis toolbox. It will take a shapefile stream network, that does not contain ...
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