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chasward

01/11/2016 13:10:17

We currently have an issue specifying resurvey to be located exactly on the site of historic survey cross-sections: ok, a practicable definition of ‘exactly’. The distance between reach cross-sections is currently an inexact science due to the lack of a centre line. Whilst any uncertainty can be constrained by referencing chainage as relative between key structures, there is no absolute. For the reason of repeatability, it would be good to be able to record a polyline string for centre-line (this may be as step towards EACSD). It would also be useful to identify LOB and ROB over bank distances as polylines. This would be useful for unambiguous recording of current bank lengths and repeatability of measurement – robust data! It would also come in useful for instances such as bank washouts and engineered short-cutting. An ability to read  grid elevations into the LOB / ROB strings would be useful. This would enable a precise tie-up between the 1d and 2d domains - the overbank elevation data could be output for use as z-lines.

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Bob

Flood Modeller Support

01/11/2016 17:12:11

Hi

I may have misunderstood your request, but do you require the generation of a centreline through the cross sections of a 1D network? If so then there may two functions that could provide help:

1. If you drag the network onto the map so that the cross section lines are displayed in the map view, you can then select the network file in the Layers panel (lower left corner of interface) and use the Generate River Centreline tool in the tool box. This will automatically join up the lowset poinst in each cross section as a new polyline shapefile. However, it may not join between reaches (i.e. it stops when distance to next = 0 signifiying the end of a reach) and so some manual drawing using the shapefile editor (with snapping to the centreline on) may be required if you require a continuous line.

2. Alternatively if you right click on a 1D network in the Project panel (upper left corner of interface) there is a menu option to export the displayed link lines as a standalone polyline shapefile.

One thing to note once you have a centreline is that it can be used to recalculate distance to next chainage values for your river sections - there is a tool to do this in the toolbox, which again requires the sections to be dragged onto the map and selected in the Layers panel.

With respect to LOB and ROB locations there currently is no functionality to export these data as a polyline. However, you can use the coordinate extraction functionality in TabularCSV to extract these points from a 1D network as a csv format text file. You can then use the csv to shapefile tool to display these data on the map as a new point shapefile.

Finally with v4.2, if you have bank edge markers defined in your 1D network then these can be changed to deactivation markers (there is a tool to do this automatically for an entire network), then when you drag the sections onto the map only the active portion of each section will be displayed, enabling you to snap the active area of a 2D model of the floodplain precisely to the bank edge location.

I hope there are some useful workarounds here to give you something close to what you are requesting. If this is not quite what you need then please let me know via this forum post.

Thanks and regards

Bob

 

chasward

02/11/2016 09:12:33

Hi Bob, thanks for taking the time to respond.

The centre-line functionality sounds like it should do what we need.

Also, thanks for the tips on LOB / ROB locations, I'm sure we can put those to use.

You are correct in that it is something close, but not quite what I was asking. The distance node-node might be a little linear where, as you'll appreciate the purpose of LOB / ROB is to represent the circuitousness of the banks. It would be best (imho) to record this within the model files rather than refer to out-of-model records. As stated, if implemented, this could be particularly useful for snapping the 2d domain, appreciating your answer, but for the LOB / ROB rather than just directly node to node  (also appreciating the principles of Mandelbrot's measurement of the coastline!) and then possibly extend to offer the ability to lift elevations from the DEM and populate a spill if required.

Thanks again,

Chas

Bob

Flood Modeller Support

02/11/2016 10:59:17

Hi Chas

The automated tool I referred to that creates centrelines can only work with the 1D network data it has, i.e. the cross sections. So it will always just draw straight lines between these points. To get a better definition of bends in a river then you would need to add extra sections. Or to get the extra distance related to travelling around a bend between sections you would need to manually draw a polyline shapefile to follow the bends and then use this as the source data in the tool that calculates distance to next section.

Differences between the inside and outside of bends (along LOB or ROB) are defined in a section by relative path length values (RPL). There could be scope here to add a tool to calculate RPL factors based on user specified polylines defining centreline, LOB and ROB - I could add this to our development list for future consideration (when it would be done would then depend on degree of further support of the idea from other users).

For lifting bank elevations from the underlying DEM have you tried the Spill Generator tool? This takes a specified polyline shapefile and calculates spill lines. The input line does not have to follow the precise high points of banks as the tool "draws" mini cross sections at each spill point and searches for max elevations in the specified DEM. You can set the number of spill points per spill, length of each "search" section and number of search points on each section. The output is a sec file format (i.e. a dat file without the header and footer metadata), which can then be imported into a 1D network using the import nodes function (right-click menu on network table > File > import model nodes). In addition the spill generator outputs various shapefiles that were generated as part of the process and these could be useful then to snap to when defining a 2D active area.

Hope this provides more useful information on Flood Modeller functions.

Regards

Bob

 

 

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