Non compute polygons

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epelde.ane@gmail.com
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Non compute polygons

Postby epelde.ane@gmail.com » Mon Dec 19, 2011 11:07

Hello all,

Through the modify grid data tool you can transform points to non compute points, but, is there any way of creating a polygon and non computing it? I´ve tried doing a polygon above a layer and I see that when I change the zoom, the polygon remains with the same size. So, cant I create a polygon that goes from cell to cell so that it doesnt matter with which zoom I´m looking at it?

Thanks again,
ane

epelde.ane@gmail.com
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Re: Non compute polygons

Postby epelde.ane@gmail.com » Mon Dec 19, 2011 18:35

Hello again :)
What I have done to non compute an area has been by cell by cell with the tool modify and closing points with values of -99. Then, I delineated the watershed so that I have new files of the delineation and drainage network.
Would it be adviseable to construct the rest of files (using delineate watershed and porous media tools)?
And, althought I dont do it, how does mohid know that I´ve changed the DTM? With the file path to the drainage network file? I think that is it, cause that was constructed with the treshold value I give in the delineate watershed tool and with the DTM with no depressions, and it is the only value I change in the modules..so, can anyone tell me if I´m right, please?

Thanks

davidbrito
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Re: Non compute polygons

Postby davidbrito » Mon Dec 19, 2011 18:57

Hello Ane,

When you change DTM you have to go to process of removing depressions and generating river and cross sections and porous media bottom...

The construction of the DTM from points allow you to select a poligon feature to remove the are from calculations (with giving the value -99 as you said).


David

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Re: Non compute polygons

Postby epelde.ane@gmail.com » Mon Dec 19, 2011 19:19

Do I have to remove depression again although I have selected the non compute cells in the grid data file with no depressions?

Aaaa.. I see. So if I want to change the delineation I have to do everything again. I didnt remember where I had seen the option to generate a file and choose the non compute areas.. I see that it is in the fist step..

Thanks!

davidbrito
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Re: Non compute polygons

Postby davidbrito » Mon Dec 19, 2011 19:32

yes if you change the dtm (change altitudes) even that you change it after the DMT_NoDepressions, you are changing the DTM and if you analyse it again for depressions it may happen that it finds other depressions that did not existed previously.


But if your only change is put some cells -99 (as you not change altitudes just remove cells) it may pass. but check it again.


David

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Re: Non compute polygons

Postby epelde.ane@gmail.com » Thu Dec 22, 2011 10:42

Hello!
Can anyone explain me please how does work the -99 value? For instance, what happens if you are creating a DTM and you give -99 value to a cell surrounded by other cells (i mean, one cell it isn´t in the outer part of the catchment). And, related to this, mohid just compute and calculate flow within the delineation of the catchment, doesnt it?

When we have time series and a lack of data of a porperty which is not realistic to stimate (by calculating the mean...), e.g. precipitation, do I have to write -99 as well?
Thanks!

frank.maretec@ist.utl.pt
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Re: Non compute polygons

Postby frank.maretec@ist.utl.pt » Wed Jan 04, 2012 12:29

Dear Ane,

in the DTM, -99 indicates non compute points. They can only exist in the outer part of the catchment. You can't create "holes" inside your catchment.
You are right about the calculation. It's only done inside the delineated area. There is a especial case. You can set the keyword
DELINEATE_BASIN (in the Basin Geometry data file) to false. In this case, the model will calculate flow in every grid cell (less the ones which have -99), but you can't use the drainage network module. So you must route the channel flow with the runoff module. In this particular case you can also create "holes"... (not sure about that).

You can't use the -99 option to fill gaps in the time series.

You have to invent a value or simply omit the row. Then MOHID will linearly interpolate the data (if you provide intensity in form of mm/h) or consider the next value for the accumulated period (if you provide rain in mm).

I strongly recommend that you provide rain in measured, accumulated values with a frequency not higher than 1 hour. Then you can make a series like this:
0h 0mm
1h 5mm
2h 10mm
4h 10mm

This means that:
From 0h to 1h it rained 5mm -> intensity will be 5mm/h
From 1h to 2h it rained 10mm -> intensity will be 10mm/h
From 2h to 4h it rained 10mm -> intensity will be 5mm/h

If you use daily values, MOHID will distribute them uniformly, which usually is not the case in nature, especially in southern countries were rain events are more concentrated in time and in space

Hope this helps,
Frank
In order to understand recursivity you must first understand recursivity.

epelde.ane@gmail.com
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Re: Non compute polygons

Postby epelde.ane@gmail.com » Wed Jan 04, 2012 13:19

Ok, so if I have wrong values I´ll just take off the rows.. And, about the acumulative parameters, I´ve to set accumulate_values:1 just to precipitation, don´t I? In the case of the rest of parameters (wind, humidity, temperature..) I guess I can leave it as I had.
About the periodicity of the data, I have all the climatic data in 10min time step, so I was calculating the hourly values from it. Do you recommend to start working with 10minutely data or for now I can go on with the hourly one? If I change this, I guess it´ll take much more time for the simulations...
Best regards,
ane

frank.maretec@ist.utl.pt
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Re: Non compute polygons

Postby frank.maretec@ist.utl.pt » Wed Jan 04, 2012 14:32

Dear Ane,

yes, it's right. The accumulate values are only for precipitation (if provided in mm instead of mm/h). All other properties should have accumulate set to false.

If you have 10min data, use it! The model will not run slower because of this (Model time step is shorten then 10min, at least during rain).

Happy MOHIDing,
Frank
In order to understand recursivity you must first understand recursivity.


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