keep turtles off wall and on grid

[rbsoc...@gmail.com]

I have two breeds of turtles, call them mobiles and immobiles.  In my model the mobiles visit one immobile and then move to the next immobile and so forth.  My problem is when both breeds are set with:

setxy random-xcor random-ycor

some of the turtles are partially or wholly off the grid.  How can I set both breeds so they are off the walls and completely visible?

Thanks, RB

[James Steiner]

Correction: below in using Setxy, I meant world-height in the formula that sets the ycor. 

Setxy 

Min-pxcor + random (world-width - 1)

Min-pycor + random (world-height - 1)

—James

On Mon, Dec 20, 2021 at 3:56 PM James Steiner <grego...@gmail.com> wrote:

It’s worth noting that NetLogo is not a grid like we tend to think of a grid… the patches centers are the integer locations. 

This means that for a world with the min-pxcor of -5 and max-pxcor of 5,

There are 11 patches  across

There is a line of patches at xcor = 0

The minimum xcor is -5.5.

The maximum xcor is 5.4999…

The world-width is 11

But (Max-pxcor - min-pxcor) is 10

So, placing turtles at random xcor and ycor means some of those turtles (drawn with size 1 shapes) may hang over the edge. 

If you want them at patch-centers, use random-p_cor

If you want them at random locations except for a border around the edge, so none hang over, use 

Setxy 

Min-pxcor + Random (world-width - 1)

Min-pycor + random (Workd-width - 1)

If your are using a turtle size other than 1, to get the same visual effect you’ll have to adjust the above to account for size. 

E.g.

Let gap (size - 1) / 2

Setxy

Min-pxcor + gap + (random (world-width - 1 - gap - gap)

… and so on

Note that doing this means your turtles are no longer evenly distributed, in that a .5 patch border is always empty. Be aware this can cause undesired biases or other artifacts in some models. 

Hope this helps

~~James

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[James Steiner]

It’s worth noting that NetLogo is not a grid like we tend to think of a grid… the patches centers are the integer locations. 

This means that for a world with the min-pxcor of -5 and max-pxcor of 5,

There are 11 patches  across

There is a line of patches at xcor = 0

The minimum xcor is -5.5.

The maximum xcor is 5.4999…

The world-width is 11

But (Max-pxcor - min-pxcor) is 10

So, placing turtles at random xcor and ycor means some of those turtles (drawn with size 1 shapes) may hang over the edge. 

If you want them at patch-centers, use random-p_cor

If you want them at random locations except for a border around the edge, so none hang over, use 

Setxy 

Min-pxcor + Random (world-width - 1)

Min-pycor + random (Workd-width - 1)

If your are using a turtle size other than 1, to get the same visual effect you’ll have to adjust the above to account for size. 

E.g.

Let gap (size - 1) / 2

Setxy

Min-pxcor + gap + (random (world-width - 1 - gap - gap)

… and so on

Note that doing this means your turtles are no longer evenly distributed, in that a .5 patch border is always empty. Be aware this can cause undesired biases or other artifacts in some models. 

Hope this helps

~~James

On Mon, Dec 20, 2021 at 1:27 PM rbsoc...@gmail.com <rbsoc...@gmail.com> wrote:

--

[Wade Schuette]

@James Steiner  Wow,  there's some unexpected info that will come in handy someday!

Seriously. 

As the Chinese Poet Li Po noted centuries ago:

 

Tremble, be fearful

Night and day be careful.

Men do not trip over mountains;

they fall over earth mounds.

Happy holidays!

Wade

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[rbsoc...@gmail.com]

Thanks all for both concrete advice and Chinese poetry.  Logic behind grid construction interesting.

A second to a happy and healthy holiday.

Best, RB

[Leo Niehorster-Cook]

Another good option might be:

ask turtles [ move-to one-of patches ]

This way, each turtle chooses a specific patch, then moves directly to its center.

Cheers!

Leo