CODEWITHSUNDEEP
c#gisgeospatialarcgisdotspatial
Shoaib Ijaz
Shoaib Ijaz

Reputation: 5587

Creating features(point) grid on polygon

I am working on GIS based desktop application using C#. I am using dotspatial library in this project.

Now I need to create a grid of features on polygon. This grid cell (rectangle) should be 20*20 Meter Square.

I have worked on it and able to create grid but facing issue regarding to cell size. Whenever polygon size changed cell size also reduced. My code.

         // Polygon Width = 2335
        // Polygon Height = 2054

        int RowsCount = 111;
        int ColumnsCount = 111;

        var maxPointX = Polygon.Extent.MaxPointX;
        var minPointX = Polygon.Extent.MinPointX;

        var maxPointY = Polygon.Extent.MaxPointY;
        var minPointY = Polygon.Extent.MinPointY;

        var dXStep = (maxPointX - minPointX) / (ColumnsCount - 1);
        var dYStep = (maxPointY - minPointY) / (RowsCount - 1);

        var gridColumnsPoints = new double[1000000];
        var gridRowPoints = new double[1000000];

        //   Calculate the coordinates of grid
        var nextPointX = minPointX;

        for (int i = 1; i <= ColumnsCount; i++)
        {
            gridColumnsPoints[i - 1] = nextPointX;
            nextPointX = nextPointX + dXStep;
        }

        var nextPointY = minPointY;

        for (int i = 1; i <= RowsCount; i++)
        {
            gridRowPoints[i - 1] = nextPointY;
            nextPointY = nextPointY + dYStep;
        }

Output enter image description here

Now when I tried this code on small size of Polygon then grid cell size also decreased.

enter image description here

I know my approach is not correct, So I have searched on it and got some tools. like

https://gis.stackexchange.com/questions/79681/creating-spatially-projected-polygon-grid-with-arcmap

But I want to create it in C# and unable to found any algorithm or any other helping material.

Please share your knowledge. Thanks

Upvotes: 0

Views: 901

Answers (2)

user1562155
user1562155

Reputation:

The problem is here:

    var dXStep = (maxPointX - minPointX) / (ColumnsCount - 1);
    var dYStep = (maxPointY - minPointY) / (RowsCount - 1);

because it makes the grid size dependent on the polygon, but it should be fixed to the scale of the view.

I'm not familiar with the dotspatial framwork, but you must operate in a coordinate system of a kind. You should align your grid to that coordinate system by calculating the first x pos to the left of the polygon in some distance from the polygons bounding box (max/min) and then step with the resolution of the coordinate system through to the max X of the polygon.

Upvotes: 1

T Kambi
T Kambi

Reputation: 1387

I am not able to understand, if you want the grid cell size to be 20*20 meters, how does the size change from polygon to polygon. It should always be 20*20 meters.

In you code, where did you get the values for ColumnsCount and RowsCount?

Your dx and dy should always be 20 (if the spatial reference units are in meters) or you need to convert the 20 meters to appropriate length of units of the spatial reference.

Pseudo code for creating grid:

var xMax = Polygon.extent.xmax;
var xMin = Polygon.extent.xmin;
var yMax = Polygon.extent.ymax;
var yMin = Polygon.extent.ymin;

var gridCells = [];
var x = xMin, y = yMin;

while(x <= xMax){
    var dx = x + 20;

    while(y <= yMax){
        var dy = y + 20;

        var cell = new Extent(x, y, dx, dy);
        gridCells.push(cell);

        y = dy;
    }
    x = dx;
}

Upvotes: 1

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