Hi, we don't linearly scale the radius, we linearly scale the area of the bubbles. I tested this with 5 values: 500, 525, 550, 575, and 600, with a sizeAxis from 10 to 20. The circles I got had the radii 10, 13, 16, 18, and 20, respectively. Here is how we figure out the radius of a bubble: // Normalize the value value = (value - minValue) / (maxValue - minValue) // Convert the minimum radius to a minimum area value // The formula to calculate the area of a circle is 2 * pi * r ^ 2 minArea = minRadius ^ 2 * 2 * pi maxArea = maxRadius ^ 2 * 2 * pi // Figure out the area of the bubble bubbleArea = (maxArea - minArea) * value + minArea // Convert the bubble area back to the radius bubbleRadius = sqrt(bubbleArea / 2 / pi)
Here it is, worked out, for every one of my points (excluding the trivial min and max values): value = (525 - 500) / (600 - 500) = 25 / 100 = 0.25 minArea = 10 ^ 2 * 2 * pi = 200 * pi maxArea = 20 ^ 2 * 2 * pi = 800 * pi bubbleArea = (800*pi - 200*pi) * 0.25 + 200*pi = (600*pi) * .25 + 200*pi = 150*pi + 200*pi = 350*pi bubbleRadius = sqrt(350*pi / 2 / pi) = sqrt(175) = 13.23 value = (550 - 500) / (600 - 500) = 50 / 100 = 0.5 minArea = 10 ^ 2 * 2 * pi = 200 * pi maxArea = 20 ^ 2 * 2 * pi = 800 * pi bubbleArea = (800*pi - 200*pi) * 0.5 + 200*pi = (600*pi) * 0.5 + 200*pi = 300*pi + 200*pi = 500*pi bubbleRadius = sqrt(500*pi / 2 / pi) = sqrt(250) = 15.81 value = (575 - 500) / (600 - 500) = 75 / 100 = 0.75 minArea = 10 ^ 2 * 2 * pi = 200 * pi maxArea = 20 ^ 2 * 2 * pi = 800 * pi bubbleArea = (800*pi - 200*pi) * 0.75 + 200*pi = (600*pi) * 0.75 + 200*pi = 450*pi + 200*pi = 650*pi bubbleRadius = sqrt(650*pi / 2 / pi) = sqrt(325) = 18.03 Rounded, these sizes match up to the radii that were calculated for my bubble chart. I hope this helped you understand our logic a bit better. - Sergey On Thu, Jan 30, 2014 at 5:12 AM, Cyril Trümpler <[email protected]>wrote: > Hello, > > I encounter a strange behavior with bubble size in a bubble chart. > Bubble size scale is not proportional with minimal value: (with / without > override sizeAxis.minSize options) > - a data entry with a value of 500 has a radius of 5 (sizeAxis.minSize > default) > - another data entry with a value of 530 has a radius of 17 > - last entry with a value of 550 has a radius of 22 > > The last two seems proportional. > > You can play with the following dataset on playground: > > ['Name', 'Val1', 'IRR', 'Region', 'Size'], > ['Fund I', 80.66, 1.67, 'North America', 500], > ['Fund II', 80.66, 1.57, 'Asia', 530], > ['Fund III', 79.84, 1.36, 'Europe', 550] > > I should expect something like (fictive values here): > 500 => 5 > 530 => 7 > 550 => 10 > > Is there a way to override this or this is a bug? > > Thanks > > -- > You received this message because you are subscribed to the Google Groups > "Google Visualization API" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to > [email protected]. > Visit this group at > http://groups.google.com/group/google-visualization-api. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "Google Visualization API" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-visualization-api. For more options, visit https://groups.google.com/groups/opt_out.
