Fix synoptic chart rasterization: switch to pdftoppmHEADmaster

BOM's IDY00030 chart-generator update on 2026-08-26 exposed an upstream
Ghostscript bug where magick's PDF delegate silently drops all page
content but isobars at production DPI. Poppler's pdftoppm renders the
same PDFs correctly, so it now does the rasterization step and magick
just resizes. Records the incident, remediation, and a separate
unfixable BOM-side monochrome-fill defect in doc/rtfm.md.

1 files changed, 8 insertions, 2 deletions

diff --git a/synopticChart.sh b/synopticChart.sh
index 059665d..2da65c0 100755
--- a/synopticChart.sh
+++ b/synopticChart.sh
@@ -21,7 +21,7 @@ require_cmd() {
 
 require_cmd curl
 require_cmd magick
-require_cmd gs
+require_cmd pdftoppm
 
 # Return the datetime string for the most recently published chart slot.
 # BOM chart slots: 0000, 0600, 1200, 1800 UTC.
@@ -54,7 +54,13 @@ if [ "$curlExit" -gt 0 ]; then
     exit "$curlExit"
 fi
 
-magick -density 300 "${latestChart}" -resize 1920x1080 "${dateTime}.png"
+# pdftoppm (Poppler), not magick's Ghostscript delegate, does the actual PDF
+# rasterization: at 300dpi, gs silently drops all page content but the
+# isobars on BOM's current chart-generator output (confirmed upstream
+# Ghostscript bug, not fixable here) — see doc/rtfm.md.
+pdftoppm -r 300 -png "${latestChart}" "${dateTime}"
+magick "${dateTime}-1.png" -resize 1920x1080 "${dateTime}.png"
+rm -f "${dateTime}-1.png"
 
 mv "${latestChart}" "${RAW_DIR}/"
 cp "${dateTime}.png" "${ARCHIVE_DIR}/"