I have been using the library draw2d with go-nexrad, and I am able to generate PNG and SVG files. However, the SVG files that are generated are enormous, with a less than 10MB PNG file becoming a 28MB SVG file with the same options. Here is the code:
func render(out string, radials []*archive2.Message31, label string) {
width := float64(imageSize)
height := float64(imageSize)
PNGcanvas := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
draw.Draw(PNGcanvas, PNGcanvas.Bounds(), image.Black, image.ZP, draw.Src)
PNGgc := draw2dimg.NewGraphicContext(PNGcanvas)
SVGcanvas := draw2dsvg.NewSvg()
SVGcanvas.Width = strconv.Itoa(int(width)) + "px"
SVGcanvas.Height = strconv.Itoa(int(width)) + "px"
SVGgc := draw2dsvg.NewGraphicContext(SVGcanvas)
xc := width / 2
yc := height / 2
pxPerKm := width / 2 / 460
firstGatePx := float64(radials[0].ReflectivityData.DataMomentRange) / 1000 * pxPerKm
gateIntervalKm := float64(radials[0].ReflectivityData.DataMomentRangeSampleInterval) / 1000
gateWidthPx := gateIntervalKm * pxPerKm
t := time.Now()
log.Println("rendering radials")
// valueDist := map[float32]int{}
for _, radial := range radials {
// round to the nearest rounded azimuth for the given resolution.
// ex: for radial 20.5432, round to 20.5
azimuthAngle := float64(radial.Header.AzimuthAngle) - 90
if azimuthAngle < 0 {
azimuthAngle = 360.0 + azimuthAngle
}
azimuthSpacing := radial.Header.AzimuthResolutionSpacing()
azimuth := math.Floor(azimuthAngle)
if math.Floor(azimuthAngle+azimuthSpacing) > azimuth {
azimuth += azimuthSpacing
}
startAngle := azimuth * (math.Pi / 180.0) /* angles are specified */
endAngle := azimuthSpacing * (math.Pi / 180.0) /* clockwise in radians */
// start drawing gates from the start of the first gate
distanceX, distanceY := firstGatePx, firstGatePx
if vectorize == "png" {
PNGgc.SetLineWidth(gateWidthPx + 1)
} else if vectorize == "svg" {
SVGgc.SetLineWidth(gateWidthPx + 1)
}
if vectorize == "png" {
PNGgc.SetLineCap(draw2d.ButtCap)
} else if vectorize == "svg" {
SVGgc.SetLineCap(draw2d.ButtCap)
}
var gates []float32
switch product {
case "vel":
gates = radial.VelocityData.ScaledData()
case "sw":
gates = radial.SwData.ScaledData()
case "rho":
gates = radial.RhoData.ScaledData()
default:
gates = radial.ReflectivityData.ScaledData()
}
numGates := len(gates)
for i, v := range gates {
if v != archive2.MomentDataBelowThreshold {
//fmt.Println(gateWidthPx)
if i == 0 {
SVGgc.SetLineWidth(0)
} else if i > 0 {
SVGgc.SetLineWidth(gateWidthPx + 1)
}
// valueDist[v] += 1
if vectorize == "png" {
PNGgc.MoveTo(xc+math.Cos(startAngle)*distanceX, yc+math.Sin(startAngle)*distanceY)
} else if vectorize == "svg" {
SVGgc.MoveTo(xc+math.Cos(startAngle)*distanceX, yc+math.Sin(startAngle)*distanceY)
}
// make the gates connect visually by extending arcs so there is no space between adjacent gates.
if i == 0 {
if vectorize == "png" {
PNGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle-.001, endAngle+.001)
} else if vectorize == "svg" {
SVGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle-.001, endAngle+.001)
}
} else if i == numGates-1 {
if vectorize == "png" {
PNGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle, endAngle)
} else if vectorize == "svg" {
SVGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle, endAngle)
}
} else {
if vectorize == "png" {
PNGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle, endAngle+.001)
} else if vectorize == "svg" {
SVGgc.ArcTo(xc, yc, distanceX, distanceY, startAngle, endAngle+.001)
}
}
if vectorize == "png" {
PNGgc.SetStrokeColor(colorSchemes[product][colorScheme](v))
} else if vectorize == "svg" {
SVGgc.SetStrokeColor(colorSchemes[product][colorScheme](v))
}
if vectorize == "png" {
PNGgc.Stroke()
} else if vectorize == "svg" {
SVGgc.Stroke()
}
}
distanceX += gateWidthPx
distanceY += gateWidthPx
azimuth += radial.Header.AzimuthResolutionSpacing()
}
}
// fmt.Println(valueDist)
if renderLabel {
if vectorize == "png" {
addLabel(PNGcanvas, int(width-495.0), int(height-10.0), label)
} else if vectorize == "svg" {
logrus.Warn("Labels cannot be drawn on an SVG image, ignoring -L flag")
}
}
// Save to file
if vectorize == "png" {
draw2dimg.SaveToPngFile(out, PNGcanvas)
fmt.Println("Finished in", time.Since(t))
} else if vectorize == "svg" {
draw2dsvg.SaveToSvgFile(out, SVGcanvas)
fmt.Println("Finished in", time.Since(t))
}
}
The full file can be found in my fork of the project here.
The reason I think the SVG is so large is because it is generating the file very inefficiently, possibly by trying to render every pixel instead of just a start and end point. I have tried setting the DPI with SVGgc.setDPI(), but that hasn't worked.
If anyone has any idea about why the file is so large, or any idea of how to fix it, I would greatly appreciate your input. Hopefully you won't have to go through the entire go-nexrad project to understand this, I have included the code block that I am almost certain is causing the issue, and is the part that uses the library.
