colorzones!

colorzones!(shapes::Vector{GMTdataset}[, fun::Function]; img::GMTimage=nothing,
	          url::AbstractString="", layer=0, pixelsize::Int=0, append::Bool=true)

keywords: GMT, Julia, images, zonal colors

Paint the polygons in the shapes with the average color that those polygons ocupy in the img image. When the shapes are plotted the resulting image looks like a choropleth map. Alternatively, instead of transmitting the img image one can provide a WMS URL, layer number and pixelsize to download images from the Web Map Server service, covering each one the bounding box of each of the shapes polygons. This option is much slower than passing the entire image at once but consumes much less memory. Important when the total area is large (think Russia size) because even at a moderately resultion it can imply downloading a huge file.

• shapes: A vector of GMTdataset containing the polygons to be painted. This container will be changed in the sense that the header field of each polygon (a GMTdataset) will be appended with the fill color (but see also the append option that controls how this change takes place.)

• fun: By default, the average color is obtained by taking the square root of the average of squares of each of the three (RGB) bands (or just one for grayscale images). Give the name of another function to replace this default. For example, median will assign the color by computing the median of each component inside the polygon area in question.

• img: the image from which the stats (fun) of each color for each polygon will be computed.

• url: In case the img option is not used, pass the Web Map Server URL (see the wmsinfo and wmsread functions) from where the the images covering the BoundingBox of each polygon will be downloaded. Warning, this is a much slower method but potentially useful when the images to download risk to be very big.

• layer: When the url option is used this one becomes mandatory and represents the layer number or layer name of interest from those provided by the WMS service. That is, both forms are allowed: layer=3 or layer="Invented layer name"

• pixelsize: Sets the requested cell size in meters [default]. Use a string appended with a 'd' (e.g. resolution="0.001d") if the resolution is given in degrees. This way works only when the layer is in geogs.

• append: By default, the color assignment to each of the polygons in the shapes vector is achieved by appending the fill color to the possibly existing header field. Running the colorzones command more than once keeps adding (now ignored, because only the first is used) colors. Setting append=false forces rewriting the header field at each run and hence the assigned color is always the one used (but the previous header is cleared out).

Returns

It does't return anything but the input GI is modified.

Examples

Read the 2020 Sentinel2 Earth color for Portugal at 100 m resolution. Load the administrative regions and compute their median colors.

wms = wmsinfo("http://tiles.maps.eox.at/wms?");
img = wmsread(wms, layer=3, region=(-9.6,-6,36.9,42.2), pixelsize=100);
Pt = gmtread("C:/programs/compa_libs/covid19pt/extra/mapas/concelhos/concelhos.shp");
colorzones!(Pt, median, img=img);
imshow(Pt, proj=:guess)

See Also

rasterzones!, gmtread, wmsinfo, wmsread