## Curvilinear Grid Generator

MOHID GIS general discussion forum
paulo.chambel.maretec@taguspark.pt
Posts: 29
Joined: Thu Jan 01, 1970 00:00
Location: Taguspark
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### Curvilinear Grid Generator

What is the name of the program that is used to generate curvilinear grids? How can I download the last version? In what directory the grid generater should be placed ? What are the steps in MohidGis to generate a curvilinear grid?

hernanitheias@netcabo.pt
MOHID Beginner
Posts: 19
Joined: Thu Jan 01, 1970 00:00
Dear Paulo,

Indeed we have just finished implementing GRIDGEN, a grid generator that produces nice structured curvilinear meshes. Thank you for your interest.

The grid generator comes with MOHID GIS. In order to have it you must download the latest version of MOHID (version 4.1) and install it.

HOW TO USE GRIDGEN?

You need to add to your project the polygon that will be the boundary of your meshing domain
2) Render Vertices
In order to 'prepare' your polygon for meshing you will need to define corners (this will be explained later). So you need to activate 'render vertices' to manipulate the vertices of the polygon. For that, right-click your polygon in the dataitem list, choose 'properties' and then check the 'render vertices' checkbox. Verify that the size of the font associated to the polygon is in agreement with the scales you are using (otherwise you might see nothing).
3) Define Corners
Next step is to define the corners of the polygon. Corners are used to pave a domain in simpler sub-domains for meshing.

You always have to mark at least 4 right turn corners and this corresponds to a simple polygon. For a complex polygon one should decompose the domain in many sub-domains.The topology of any meshed sub-domain is a four edges polygon and it is defined with 2 left turns and 2 right turns (cf. picture: upper domain on the second example).
Your polygon should have at least 4 right turns and the sum of right turns minus the sum of left turns should always be 4. Otherwise the program gives an error.

To define corners go to \"Action->Polygons->Corners Definition\". One left click on a vertex turns it into a right turn. A 'R' should appear near the vertex - if it doesn't, check size of font in polygon properties as explained before. A second click will turn it into a left turn ('R' turn to 'L'). A third click will turn the vertex to a non-corner vertex (the letter dissapears). An so on.

4)Generate the grid

Go to \"DataItems->New\". Check the \"Curvilinear Grid\" option and OK.
Choose values for NX, NY and NPPE and then OK.
NX and NY are the number of intervals of your grid in the X and Y direction respectively.
NPPE is the Number of Points Per Edge. It is the minimum number of grid vertices you will have between two consecutive vertices of your boundary.

The program hasn't been tested a lot for the moment, so we would appreciate any feedback on it.

Hernâni Theias
MARETEC

rafael_cabral_goncalves@yahoo.com.br
MOHID Beginner
Posts: 1
Joined: Thu Jan 01, 1970 00:00

### Actualizing step 3

In step \"3) Define Corners\", Hernâni said:

To define corners go to \"Action->Polygons->Corners Definition\".

I'm using Mohid GIS version 4.9.X and I didn't find the path \"Action -> Polygons -> Corners Definition\".

I found the Corners Definition option in the combo box located at the second line of buttons. Between the properties and normal select buttons.

The option is \"Define Polygon Corners\".

-----------------------------
Rafael Cabral Gonçalves
SANEPAR
Curitiba-PR-Brasil

camillecouzi@yahoo.fr
MOHID User
Posts: 33
Joined: Thu Jan 01, 1970 00:00
Hi Mohiders,
I post a reply on this very old message because I am having some troubles about curvilinear grids.
I have my line coasts, then I press data Item -> New data item-> curvilinear grid, then i select my boundary (line coast), and then big question: qhat is NPPE?!!! It isn't explained nowhere!!!!!

I have also another question: I am beginning using the Triangle aplication on Matlab (another program used to do triangular grids), is there any way to make my grid on Triangle, and then pass it on the mohid format?

Thank you very mucho for your help...

Camille.

luis_at_mohid.com
MOHID Developer
Posts: 553
Joined: Thu Jan 01, 1970 00:00
Location: Instituto Superior Técnico - Technical University of Lisbon
Contact:
Hi Camille,

NPPE is the Number of Points Per Edge. It is the minimum number of grid vertices you will have between two consecutive vertices of your boundary.

Best regards,
Luis