cant get a dem right

[Srirama Bhamidipati]

Hi,

I am trying to create a dem from ArcGIS exported 8bit png file, with the following code. But it looks very weird. Can somebody suggest if I am missing something or may be there is a proper procedure to export a .png (attached is a png)

model study_dem

global {

/** Insert the global definitions, variables and actions here */

file dem <- file("../includes/ASCIITo_asc11.png");

file gridFile <- file("../dempositive20x20.asc");

}

experiment study_dem type: gui {

/** Insert here the definition of the input and output of the model */

output {

display DEM  type: opengl ambient_light:255 {

graphics 'GraphicPrimitive' {

draw dem(dem, dem);

}

}

}

}

[Srirama Bhamidipati]

Q1. Is the png itself not carrying enough/ correct information ?

Q2.  is there some scaling factor that can be used to make it look right ?

[Arnaud Grignard]

Srirama,

Can you send the model with the .png AND the. asc file

Arnaud

On Fri, Mar 14, 2014 at 11:44 PM, Srirama Bhamidipati <b.sr...@gmail.com> wrote:

Q1. Is the png itself not carrying enough/ correct information ?

Q2.  is there some scaling factor that can be used to make it look right ?

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[Srirama Bhamidipati]

I use dem twice as arguments of dem function, because mostly I do not have a texture file (satellite image) and I could not know if the second argument can be optional in that statement???

[Arnaud Grignard]

can you try this:

model study_dem

global {
    /** Insert the global definitions, variables and actions here */
    file dem <- file("../includes/ASCIITo_asc11.png");

    file gridFile <- file("../includes/dempositive20x20.asc");
    geometry shape <- rectangle(2360,2120);

   
}

experiment study_dem type: gui {
    /** Insert here the definition of the input and output of the model */
    output {
        display DEM  type: opengl ambient_light:255 {
            graphics 'GraphicPrimitive' {
                draw dem(dem, dem);
            }
        }
    }
}

by default the size of the env is the size of the image (so here 236,212) as the altitude value are store as rgb value between 0 and 255 in a 236x212 environment 255 is very high but in a environment 10 time bigger (geometry shape <- rectangle(2360,2120); )it looks ok and even smaller in env 100 times bigger geometry shape <- rectangle(23600,21200);

Concerning the drawing from asc file there is a problem is the current version of Gama that we need to fix http://code.google.com/p/gama-platform/issues/detail?id=837

On Sat, Mar 15, 2014 at 4:43 PM, Srirama Bhamidipati <b.sr...@gmail.com> wrote:

I use dem twice as arguments of dem function, because mostly I do not have a texture file (satellite image) and I could not know if the second argument can be optional in that statement???

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[Srirama Bhamidipati]

Yes, It seems to work. But when we increase the size of the environment what is being stretched ? The whole picture is my study area and I am afraid that if I increase the size of the environment will it cause problems to my .asc dem ? I will be using the dem to model flood as a grid. This grid comes from the .asc , So does changing the environment effect the grid coming from that .asc ?

regards.

Srirama

[Arnaud Grignard]

Sorry I actually the size of the environment by default is 100x100 (whatever the size of the image)

To have a better rendering without changing the size of the environment you can apply a z_factor (by default 1 but you will decrease the z by 10 if you pout dem(dem,0.1)

I've commited the 2 following operators
dem(dem)
and

dem(dem,z_facotr)

and updated the doc and the model
code.google.com/p/gama-platform/wiki/Gama3DCurrent?ts=1394883525&updated=Gama3DCurrent#From_PNG_FILE

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[Srirama Bhamidipati]

Thank you. It is working now and I can control the display.

[Srirama Bhamidipati]

Hi Arnaud,

when you say "as the altitude value are store as rgb value between 0 and 255 " , I have the following question: In my case I have  negative values in the dem because my area is a delta region below sea level, does that mean that values of my dem are normalized to fit within 0 to 255 ?

thanks

srirama

[Arnaud Grignard]

If you draw it from a png yes the value can only be betwenn 0 and 255 (if in 8 bits) so ArcGis must normalize it.

From an asc file I've never test but it "should" work with negative value

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