DRV1650-SR-POSTER-EXPORT, the "too much Antarctica" half. The big-poster renderer
stitches a grid of tiles, each drawn into an EQUAL-HEIGHT slot of the output image, and
it chose each row's latitude band by dividing the degree span evenly:
latStep = (ne.lat - sw.lat) / rows
Screen height is proportional to ln(tan(pi/4 + lat/2)), not to latitude, so equal DEGREE
bands are not equal SCREEN bands. MEASURED on a -60..75 view in 4 rows: the top band is
37.0% of the true rendered height and was being painted into 25% of the poster; the next
19.7% into 25%; the bottom 25.2% into 25%. Every row is squeezed or stretched, which is
the wrong aspect, and the bands where a degree buys the most pixels are the most
over-represented -- the Antarctica the Driver saw.
Sliced in Mercator y instead, every row is 25.0%, exactly, because that IS the screen
coordinate.
★ THIRD PLACE TODAY FOR THE SAME MISTAKE. A whiteboard chart nearly shipped with a linear
scale into degrees; a measurement harness nearly reported a false threshold by correcting
the wrong axis; and this has been shipping. Treating latitude as a screen coordinate is
the error, the conversion is one line, and it now lives in library/maps/mercator-slice.js
rather than being rediscovered a fourth time.
check-mercator-slice asserts the PROPERTY across five view/row combinations -- every band
an equal share of rendered height, contiguous, covering the span, north-first -- and its
CONTROL is the old code: degree-linear slicing must FAIL the same assertion, which it does
by 12.0 points. Without that control the test would pass on a tree where nothing changed.
A -90..90 view clamps at the Mercator limit instead of going infinite.
NOT FIXED HERE, because it is a product decision and not a defect: the export also asks
for an 8.5x11 PORTRAIT sheet (research-map.vue:1410), so a landscape map is letterboxed
onto a tall page. That is a deliberate default, it is the other half of "the wrong
vertical aspect", and changing the shape of the Driver's poster is his call, not mine.
859bb268e2