Rescaling Image in Windows Form

Question

I have a set of points I want to show on a 2000x2000 canvas. Here is an example: "61.86, 83 - 61.79, 82.91 - 61.77, 82.77 - 61.92, 82.76 - 61.75, 82.7 - 61.79, 82.58 - 61.85, 82.46 - 61.79, 82.17 - 61.72, 81.88 - 61.61, 81.61 - 61.51, 81.33 - 61.49, 81.02 - 61.33, 80.99 - 61.37, 80.83"

These points are from a 100x100 grid so the first one ought to be in the bottom right quarter of my 2000*2000 canvas.

To do this I have code that finds the biggest X and Y and then rescales.

        List<double> MinAndMax(List<Node> spots)
        {
            List<double> retValues = new List<double>();
            double xLowest = spots.Select(s => s.X).Min();
            double xHighest = spots.Select(s => s.X).Max();
            double xDifference = xHighest - xLowest;
            double yLowest = spots.Select(s => s.Y).Min();
            double yHighest = spots.Select(s => s.Y).Max();
            double yDifference = yHighest - yLowest;
            if (xLowest < yLowest)
                retValues.Add(xLowest);
            else
                retValues.Add(yLowest);

            if (xHighest < yHighest)
                retValues.Add(yHighest);
            else
                retValues.Add(xHighest);

            return retValues;
        }
        int Rescale(double oldValue, double oldMin, double oldMax, int newMin, int newMax)
        {
            return Convert.ToInt32(((oldValue - oldMin) * (newMax - newMin) / (oldMax - oldMin)) + newMin);
        }

I call it like so:

            double zoneMin, zoneMax;
            int lowestCanvas = 150, highestCanvas = 1850;

            List<Node> path = await PathMaker();
            List<double> zoneMinMax = MinAndMax(path);

            zoneMin = zoneMinMax[0];
            zoneMax = zoneMinMax[1];

            foreach (Node spot in path)
            {
                Point point = new Point();
                point.X = Rescale(spot.X, zoneMin, zoneMax, lowestCanvas, highestCanvas);
                point.Y = Rescale(spot.Y, zoneMin, zoneMax, lowestCanvas, highestCanvas);
                NodeSpot dot = new NodeSpot()
                {
                    Name = spot.Name,
                    Location = point,
                    IsInPath = true
                };
                drawingSurface1.Nodes.Add(dot);
            }
            drawingSurface1.Invalidate();

Instead of getting my little path nicely spread out, I get this odd clump in the bottom LEFT had quadrant.

I can't see where I am going wrong here. What do I need to do in order to have my 14 points spread out over the canvass?

Answer 1

Your issue is that you are returning a single min value and a single max value. You need separate min and max values for X and Y, as the ranges in each coordinate are different. In your sample data from the question the range of X is [-61.92, 61.86] and the range of Y is [80.83, 83]. Your approach will draw a frame covering [-61.92, -61.92] to [83, 83], with most of the points in one corner.

Your test fails to catch the problem as the X and Y values are the same in the test case. Create a test case where the X values are all negative and the Y values positive, this will show the issue.