Star-X development request ledger

Historical record, not the current specification. The authoritative geometry is documented in Star-X geometric context and implementation notes. In particular, the former maximum-land-distance experiment and Natural Earth vertical baseline below are superseded: the current cap is cut at fixed 60°S, preserves source-tip radius, uses zero geographic-bearing offset, and derives its 0.25/44 lower clearance entirely from the projected boundary.

Stage 1 development: implement a new C++20 projection in the file src.projections/cart0freak0-star-x.h using the same carto API as previous.

Base on the existing Cahill-Keyes implementation, but with the following modification to the geometry: The octants are split in two, with octants 1-4 (left side) as group 1 and octants 5-8 (the right side) as group 2.

Group 2 is rotated 180 degrees and placed on top of group 1 such that the geometry forms an X shape, with what would be the north pole in the middle.

Stage 2 development: variable sized maps with aspect ratio constraint

Abstract any hard-coded map sizes () into variable size map sizes with the same aspect ratio.

Use the a60::carto::frame abstraction for the size of the variable projection, aka

struct area { double x, double y}; from frame.frame_area here: src.projections/a60-carto-frame.h

Stage 3 development: document implementation and usage

Index to documentation pages: index.md

Summarize the work, methods used, numeric forumlas and other relevant implementation details in docs/star-x-implementation-notes.md

Explain and illustrate the geometric context, approach, quadrants, in docs/star-x-context.md

Bibliography, docs/star-x-bibliography.md

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Stage 4

adjust star-x projection implementation such that the gap between octant group 1 and octant group 2 is configurable. Then, set the defaults such that for the {44,22} example in generate geometry, the bottom octant is moved 2.25” higher, and the top group is lowered 2.25” lower. The goal is for them to both touch at 22”, the center of the frame. There is too much space inbetween in the current geometry-star-x-34-44.svg.

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Stage 5

add another step to the “star-x” transformation. After the first step’s flip and move, make a second step being a variable-sized enlargement centered at the center point of the page (which defaults to 120%)

add these changes to the star-x algorithm to docs/star-x-implementation-notes.md, along with the previous adjustment to close the gap in the X-geometry

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Stage 6

add another step to the “star-x” transformation. After the first and second step, make a third step illustrated as per the reference image assets.static/adhoc/geometry-star-x-34-44.with-poles.svg

this has two further modifications: 1) a star centered on the page, where the north pole would be 2) gathering the fragments of the antarctica continent into a single unified representation of the continent, centered and aligned at the bottom of the page on the y-axis matching the lowest octant in the page.

The reference image does not have antarctica to correct scale, use it as a guide to the concept instead of strict measurements, keep the correct scale in the final implementation

add these changes to the star-x algorithm to docs/star-x-implementation-notes.md

Stage 7

Clarification of the Star-X projection. Instead of placing a pre-computed antartica continent are per Stage 6 item 2, instead do the following

Compute the maximum land distance from the pole to the antartica continent, and call that ant_r. For each of the star-x quadrants, take the tip furthest from the center point of the projection in the quadrant and draw a circle of ant_r.

Re-assess the current implementation and conform to this new definition.

this version should be visible in graticules-star-x-34-44.png