Improve power line rendering

[TagaSanPedroAko]

Power lines may benefit from better, realistic rendering which takes in consideration the tags for number of conductors (cables=), number of circuits (circuits=), voltage (voltage=), tower or pole design (design=), line attachment (line_attachment) and tower or pole height (height=), similar to renders generated by osm2world.

Currently, power lines are rendered as single-circuit lines for lines on towers, and four conductors for lines on poles, regardless if it's tagged power=line or power=minor_line. It doesn't account for voltage on the lines or the properties tagged on towers or poles. Also the same line attachment is used for every structure (e.g. pin insulator on pole, suspension insulator on tower)

expected changes are as follows:

• power lines -- render single-circuit line with three cables by default (present already for lines on towers) -- render of line (whether that be power=minor_line or power=line) should not be affected by structure. power=line on power=pole exists, but should render taller pole, not the typical pole usually found for lines used for distribution. -- vary power line render depending voltage on power=line (use wider conductor spacing and taller towers or poles as voltage increases) --power=line should also render with sagged span just as how they appear in real life (power=minor_line already renders with sag). ground will not be affected, but can vary by tower design.
• power poles -- unless height is tagged, render a ~10 m pole as in present render -- render pole with single cross-arm by default, pole with two cross-arm if cables= on power line are 6, or pole with single cross-arm if cables= on power line are between 7 and 12 -- render a taller pole with cross-arms and suspension insulator if line carried is power=line or voltage= is >=50000 (50 kV). vary height depending on voltage. -- if design= is tagged, render a pole with appearance as described by the design= (see OSM wiki for photos). e.g. if design=asymmetric, render a pole with two cross-arms, the top one carrying just one insulator and the lower one two.
• transmission towers -- render lattice tower by default -- if no structure= is tagged on tower, render lattice delta tower as default, lattice three-level tower if cables= on power line are 6, and lattice six-level tower if cables= on power line are between 7 to 12 -- if tower has structure=tubular or solid render H-frame if cable has no other properties, tubular three-level tower if cables= are between 4 or 6, or tubular six-level tower if cables= on power line are between 7 to 12 -- vary tower height depending on voltage= tagged on power line. -- if design= is tagged, render the tower with appearance as described by the design= (see OSM wiki for photos). e.g. if design=donau, render a tower with two cross-arms, top ones carrying two cables (one each side) and lower ones carrying four (two each side)
• structure height -- if height= is given on tower or pole, render a structure in the given height. otherwise use default renders as explained above
• line attachments -- if line_attachment is tagged, render attachments as described on wiki (e.g. if line_attachment=anchor, render tower or pole with strain insulator. Vary length and spacing by voltage in case of structures that are part of power=line) --by default, render a tower or pole with strain insulator where line makes sharp turn (>=30 degrees).

sample screenshots:

• tower at sharp turn on 500 kV power line (map: https://www.openstreetmap.org/#map=18/53.45651/-113.61289). Streets GL should render a tower with strain insulator. Tower height should be higher, and insulators longer and conductor spacing wider (~5.5 m to scale). Also there is no sag.

• power line crossing at pole (map: https://www.openstreetmap.org/#map=19/13.75772/121.05815). Both lines are power=minor_line with cables=3. Should render just 3 cables. Crossing structure can be rendered with two cross-arms.

• high-voltage (69 kV) power line (power=line) with 3=lines supported on poles (map: https://www.openstreetmap.org/#map=18/18.01702/120.53589). Streets GL renders the line like power=minor_line. Should render the line with 3 conductors spaced wide apart given voltage (~72 cm to 1.5 m), a ground, and taller poles with insulators hanging from pole cross-arms (see details above).

[TagaSanPedroAko]

Also for consideration is rendering substation elements if mapped, and portal structures (at substations or power line crossings).

• power=portal
• power=transformer
• power=line+line=bay
• power=line+line=busbar

voltage will also be considered for renders of lines at substations.