6
votes
Accepted
Missing/inconsistent River Thames map data in Overpass Turbo
The river Thames is too large to digitize it in one single Openstreetmap way element.
Therefore, a relation is created to group all riverbanks belonging to it.
You can query that relation directly ...
- 77.1k
5
votes
Buffering river but it came out as circle
I can make a guess at what has happened. Did you "set" the coordinate system of the river to UTM 50N or did you actually reproject it? If the original line was digitized over a map in Long/...
- 15.8k
5
votes
Accepted
Detecting automatically where rivers flow, directly into the sea or into another river
You can make an overlay (intersects/touches) of your river lines with a polygon representing the sea.
Before you can do this, you need a polygon layer representing the sea. Best use data for the sea ...
- 75k
4
votes
Accepted
Split seamless polygon representing river banks into separate polygons using center lines
You can create a hexagonal grid covering the river polygons:
create table public.hexgrid as
with cte as (
select (st_hexagongrid(2.0, geom)).geom as geom --adjust the 2.0, the smaller the smoother ...
- 77.9k
3
votes
Accepted
Obtaining length of river upstream of points up to next point using ArcGIS Desktop?
RivEX does much if not all of what you are asking. For computing upstream length you would run the appropriate RivEX attribution tool to encode that into the network then transfer the lengths to your ...
- 44.6k
3
votes
Help with Anita Graser's guide on making tapered rivers. River shapefile has "width" field but expression is not working
'< 10 km2 Fluss'
Is what is stored in Anita's attribute table. It is a string field describing the flow rate of the river.
If your width field is not a string, rather a number, then you need to ...
- 16.9k
3
votes
Calculating Distance from Outlet to Dam(s) using ArcGIS Desktop?
If you are capable to populate tables of your data (links, nodes) accordingly:
I recommend networkx module, e.g. this tiny script computes distance to outlet for every node in network:
import arcpy
...
- 23.3k
3
votes
Accepted
Calculate Polygon Centerline with a LeastCostPath approach
I have spent many hours working on similar problems. I published a paper about it, even. In the Matlab toolbox presented there, I use the shortest path just like you're doing. In my experience, there ...
- 2,904
3
votes
Understanding DEM of difference results in ArcGIS Pro
Millimeters are a good guess, but to be sure, open up both of the DTM properties and examine the results. Within the properties section, you'll see the units (meters, feet, mm, furlongs, etc) that ...
- 8,386
3
votes
Finding rivers from GeoTIFF files with GDAL
There are various implementations of watersheds and hydrology delineation using the the A* algorithm. For instance in grass gis r.watershed and python pysheds.
In this instance I recommend the grass ...
- 269
3
votes
Calculating minimum river width for a route within the river in PostGIS/Python
Difficult question, the holes are tricky.
One idea would be to start by getting the lines of the polygon. The difficulty is that you need to separate them to be sure to don't have both sides in the ...
- 2,505
2
votes
Stream order from flow accumulation raster
Have a look at the GRASS addon r.stream.order. You can see an overview at here and more details in the main page
- 15.8k
2
votes
Accepted
Calculate river distance to headwater for every pixel?
Flow length and zonal statistics should do the trick.
For Flow Length, you should calculate distance upstream and use a weights raster with your stream pixels set to 1 and all non-stream pixels set ...
- 979
2
votes
Accepted
Extract polygon from stream line
If you insist on not using a DEM, you can use trace upstream from utility network analysis toolbar, and then create an convex hull of the selected network using Minimum Bounding Geometry.
But the ...
- 11.2k
2
votes
Distance from one point to multiple points WITHIN a shapefile
Use Point Distance tool: create a new feature class with just mouth point. and other points as a near features.
to calculte distance along a line, Use Linear referencing.
First convert the polylines ...
- 5,845
2
votes
Calculating percentage (or length) of stream network that is multiple channel streams using ArcGIS Desktop?
If I understand well, all your multiple channels create "islands" (portions of land surrounded by water, maybe it has a specific name) between them. Therefore you can identify the multichannels as ...
- 49.9k
2
votes
Accepted
Select a specific line length after and before a point
Try the "Service area (from layer)" algorithm in the processing toolbox. The "Vector layer representing network" will be your river network, and "Vector layer with start points" your point layer. The "...
- 27.9k
2
votes
GRASS GIS: Computing center line of raster feature representing a river
I have solved this problem numerous times. I have a Matlab solution posted here, and a Python solution is included in my (soon to be released) RivGraph package here. The function you'd be interested ...
- 2,904
2
votes
Removing bridges and dams from DEM
I am also struggling with that.
At present time, the best solution I have found is the following:
remove the bridges by doing so: (i) create a polygon for each bridge (or for all of them), (ii) ...
- 361
2
votes
Buffering river but it came out as circle
Something has gone wrong with the georeferencing of the initial map you used. When I load your files into qgis and use the measurement tool, the river is 0.12 meters from end to end. I am afraid you ...
- 3,836
2
votes
Accepted
An application for measuring river length?
There is no single application that will do what you ask as you are underestimating the complexity of the problem. Medial Axis will indeed identify a centre line but then you need to prune the network/...
- 44.6k
2
votes
Accepted
Rendering raster with fine structure at low resolution in QGIS
It would be helpful if you include a sample dataset with your question next time.
That said, I've acquired a river map from the World Resources Institute's Aqueduct Floods Hazard Maps; specifically, ...
- 1,831
2
votes
Accepted
Calculating area in QGIS, defined as zone with relative elevation compared to a river
This solution provides a workflow to do exactly what you asked for. The workflow might not be the standard way how to calculate flooded areas, but since you asked for it, here is a way how to do it ...
- 75k
2
votes
Accepted
Why are my channels generating straight lines?
What did you use to create the streams? It seems you have some low lying areas and certain hydrology algorithms do a "fill depressions" in advance to allow routing the streams. The GRASS GIS ...
- 15.8k
2
votes
Accepted
Adjusting flow direction of river based on DEM in QGIS
Solution 1
Use select by expression with this expression where DEM is the name of your raster layer (digital elevation model):
raster_value ('DEM', 1, start_point ($geometry)) <
raster_value ('DEM'...
- 75k
2
votes
Calculating minimum river width for a route within the river in PostGIS/Python
Edit:
I just realized you want the minimum river width - this answer can't help you with that, but I leave it here in case someone needs it.
Get the line length of the ST_ShortestLine between your ...
- 30.9k
2
votes
Minimized distance between points while staying INSIDE of a designated polygon
One approach is using Cost Distance tool from Spatial Analyst, i.e. raster based technique, which will produce something like this, depending on raster resolution:
For every pair of points you'll ...
- 23.3k
2
votes
Repeating label of line shapefile does not work
You should change the distance in from "No repeat" to a distance in mm
- 3,349
2
votes
Curved labeling of rivers in QGIS doesn't always work
Dynamic options are more elegant, but have the disadvantage that every time you zoom/pan, the rendering of the image generates a huge workload to comply with the settings. I propose a semi-automatic ...
- 75k
1
vote
Connecting river segments with R riverdist package
Well, I have merged all rivers now in QGIS and it seems to work (with the disadvantage of course that segments now all have the same attribute).
- 141
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