Finding the X,Y Center using a script

[Leander Tyles]

Hi, im not realy a scriptor but i know what i wanna do.

can somebody help me to find the x,y center of a peice of land using a script

this working code below already finds the land borders, so what we need to do is

find the point of intersection

 

float gJumpAmount = 0.5;

// *************************************************
// Find a land border by searching out from a
// specific coordinate for a change in land ownership.
// *************************************************
vector findBorder(string axis, vector start_vec, float jump_amount)
{
    float x = 0;
    float y = 0;
    float z = 0;
    float num = 0;
    vector newVec = ZERO_VECTOR;
    vector lastVec = ZERO_VECTOR;
    key owner1 = NULL_KEY;
    key owner2 = NULL_KEY;
    //
    // Validate axis
    //
    if ((axis != "x") && (axis != "y"))
    {
        // llSay(0,"Invalid axis passed to findBorder()");
        return ZERO_VECTOR;
    }

    //
    // Validate jump_amount
    //
    if ((integer)jump_amount >= 255)
    {
        // llSay(0,"Invalid jump amount");
        return ZERO_VECTOR;
    }
    //
    // Validate start_vec
    //
    x = getVectorAxis(0,start_vec);
    y = getVectorAxis(1,start_vec);
    z = getVectorAxis(2,start_vec);
    if (x <= 0 || y <= 0 || z <= 0)
    {
        // llSay(0,"Invalid vector passed to findBorder()");
        return ZERO_VECTOR;
    }
    
    if (x >= 255 || y >= 255 || z >= 255)
    {
        // llSay(0,"Invalid vector passed to findBorder()");
        return ZERO_VECTOR;
    }
    //
    // Are we too close to a sim border?
    //
    if (axis == "x")
        {
            if ((x + jump_amount >= 255) ||(x + jump_amount <= 0))
            {
                return ZERO_VECTOR;
            }
        }
        
    else
    {
        if ((y + jump_amount >= 255) ||(y + jump_amount <= 0))
        {
            return ZERO_VECTOR;
        }
    }
    //
    // Get owner of land at start vector
    //
    owner1 = llGetLandOwnerAt(start_vec);
    if (owner1 == NULL_KEY)
    {
        // llSay(0,"Could not determine land owner at the location");
        return ZERO_VECTOR;
    }
    //
    // Assign initial values
    //
    lastVec = start_vec;
    if (axis == "x")
    {
        num = x;
    }
    
    else
    {
        num = y;
    }
    //
    // Loop through until we find a different landowner
    //
    while ((num >= 0) && (num <= 255))
    {
        if (axis == "x")
        {
            newVec = <num, y, z> + <jump_amount, 0, 0>;
        }
        
        else
        {
            newVec = <x, num, z> + <0, jump_amount, 0>;
        }
        owner2 = llGetLandOwnerAt(newVec);
        if ((owner2 == NULL_KEY) || (owner1 != owner2))
        {
            return lastVec;
        }
        num += jump_amount;
        if ((num <= 0) || (num >= 255))
        {
        return lastVec;
        }
        lastVec = newVec;
    }
    return ZERO_VECTOR;
}

// *************************************************
// Return a particular axis from a vector
// *************************************************
float getVectorAxis(integer axis, vector vec)
{
    if ((axis < 0) || (axis > 2))
    {
        return -1;
    }
    
    list junk = llParseString2List((string)vec,[",","<",">"], []);
    if (llGetListLength(junk) != 3)
    {
        return -1;
    }
    return llList2Float(junk,axis);
}


//
// default state starts here
//
default
{
    state_entry()
    {
        llSay(0,"Touch the object to determine borders");
    }

    touch_start(integer num_detected)
    {
        // Uncomment to disallow anyone but the owner to use it
        //if (llDetectedKey(0) != llGetOwner())
        //{
            // return;
        //}

        vector BOUND_EAST = ZERO_VECTOR;
        vector BOUND_NORTH = ZERO_VECTOR;
        vector BOUND_SOUTH = ZERO_VECTOR;
        vector BOUND_WEST = ZERO_VECTOR;
        vector HOME_POS = llGetPos();
        //
        // Determine the northern boundary
        //
        BOUND_NORTH = findBorder("y",HOME_POS,gJumpAmount);
        if (BOUND_NORTH == ZERO_VECTOR)
        {
        llSay(0,"Failed to locate northern boundary");
        llResetScript();
        }
        //
        // Determine the southern boundary
        //

        BOUND_SOUTH = findBorder("y",HOME_POS,-gJumpAmount);
        if (BOUND_SOUTH == ZERO_VECTOR)
        {
            llSay(0,"Failed to locate southern boundary");
            llResetScript();
        }
        //
        // Determine the eastern boundary
        //
        BOUND_EAST = findBorder("x",HOME_POS,gJumpAmount);
        if (BOUND_EAST == ZERO_VECTOR)
        {
            llSay(0,"Failed to locate eastern boundary");
            llResetScript();
        }
        //
        // Determine the western boundary
        //
        BOUND_WEST = findBorder("x",HOME_POS,-gJumpAmount);
        if (BOUND_WEST == ZERO_VECTOR)
        {
            llSay(0,"Failed to locate western boundary");
            llResetScript();
        }
        //
        // Format some results for displaying
        //
        float borderNorth = getVectorAxis(1,BOUND_NORTH);
        float borderSouth = getVectorAxis(1,BOUND_SOUTH);
        float borderEast = getVectorAxis(0,BOUND_EAST);
        float borderWest = getVectorAxis(0,BOUND_WEST);
        float zCoord = getVectorAxis(2,HOME_POS);
        vector vectorNW = <borderNorth, borderWest, zCoord>;
        vector vectorNE = <borderNorth, borderEast, zCoord>;
        vector vectorSE = <borderSouth, borderEast, zCoord>;
        vector vectorSW = <borderSouth, borderWest, zCoord>;
        //
        // Display the results
        //

        llSay(0,"");
        llSay(0,"Northern Boundary Detected: " + (string)BOUND_NORTH);
        llSay(0,"Southern Boundary Detected: " + (string)BOUND_SOUTH);
        llSay(0,"Eastern Boudary Detected: " + (string)BOUND_EAST);
        llSay(0,"Western Boundary Detected: " + (string)BOUND_WEST);
        llSay(0,"");
        llSay(0,"Northern Border Line: " + (string)borderNorth);
        llSay(0,"Southern Border Line: " + (string)borderSouth);
        llSay(0,"Eastern Border Line: " + (string)borderEast);
        llSay(0,"Western Border Line: " + (string)borderWest);
        llSay(0,"");
        llSay(0,"Northwest Coords: " + (string)vectorNW);
        llSay(0,"Northeast Coords: " + (string)vectorNE);
        llSay(0,"Southeast Coords: " + (string)vectorSE);
        llSay(0,"Southwest Coords: " + (string)vectorSW);
    }

    on_rez(integer num)
    {
        llResetScript();
    }
}     // end

 

[Dora Gustafson]

If the land is rectangular and it looks like that is the only case you are dealing with, then:

vector center = 0.5*(vectorNE + vectorSW);

 

[Ela Talaj]

I would suppose it depends on a definition of "center". While trivial for rectangular parcels as Dora noted, it may not be trivial for other shapes, like L-shape, T-shape, etc. I made a gadget that maps a parcel or a region as a matrix of 10x10 cells for any parcel shape. Then finding a center cell is a matter of its definition.

[Nova Convair]

Whats the purpose of this?

Finding the center of a rectangle is trivial as described above.

The center of an L-shape for example can be outside of the land - not usable for placing an object then.

[Qie Niangao]

Yeah, this comes up periodically, and although it's trivial for rectangular parcels, the general case is very ugly. At one point, like Eva, I had a script that scans the entire region for pieces of a parcel (I used 4x4 cells), but there are many cases where the centroid of the parcel-matching cells is not itself inside the parcel, as Nova mentions.  (Indeed, the reason it's necessary to scan the entire region is that a parcel may be not only concave but even disjoint.)