使用Golang Draw2D时极大的SVG文件

Question

我一直在使用库 draw2d with go-nexrad ，我能够生成png和svg文件。但是，生成的SVG文件是巨大的，其中不到10MB PNG文件成为具有相同选项的28MB SVG文件。这是代码：

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))
    }
}

完整文件可以在我的项目的叉子中找到在这里。

我认为SVG之所以如此之大的原因是因为它可能通过尝试渲染每个像素而不仅仅是一个起点和终点来生成文件效率非常低。我尝试使用svggc.setdpi（）设置DPI，但这尚不起作用。

如果有人对文件如此之大，或者对如何修复该文件有任何了解，我将非常感谢您的意见。希望您不必浏览整个go-nexrad才能理解这一点，我已经包括了我几乎确定要引起的代码块，并且是使用库的部分。