The reverse engineering is not with the PDF. Martin do a good job here putting in all the therion output pdf a comment with the reference. You only have to open the file and search "thCalibrate". You found the next text:

/thCalibrate0 (X=-22.16017pt, Y=260.12132pt, L=-0.3641990570, F=42.2992656650)
/thCalibrate1 (X=1921.38345pt, Y=199.8752pt, L=-0.3608862211, F=42.2991894208)
/thCalibrate2 (X=3864.92708pt, Y=139.62904pt, L=-0.3575733981, F=42.2991130810)
/thCalibrate3 (X=-0.2183pt, Y=967.96619pt, L=-0.3641616744, F=42.3001613659)
/thCalibrate4 (X=3886.86893pt, Y=847.47388pt, L=-0.3575359218, F=42.3000087771)
/thCalibrate5 (X=21.72351pt, Y=1675.81102pt, L=-0.3641242900, F=42.3010570667)
/thCalibrate6 (X=1965.26714pt, Y=1615.56487pt, L=-0.3608113605, F=42.3009808177)
/thCalibrate7 (X=3908.81078pt, Y=1555.31871pt, L=-0.3574984437, F=42.3009044731)
/thCalibrate8 (X=1943.32529pt, Y=907.72003pt, L=-0.3608487917, F=42.3000851193)
/thCalibrate (HS=3913.97253pt, VS=1573.34683pt, HD=546.7244489428)

All the information is here: pdf coordinates (X,Y), real coordinates (L,F) and the pdf width (HS) and height (VS).

You only need know the width and height from the generate PGN, and you have all the data to do the calculation.

The reverse engineering is to understand the ".map" format and found in the tcl file (mapcalc.tc) the equations to do the conversion.

Regards,

Evaristo.

El 26/03/2018 a las 12:57, Nikita Kozlov via Therion escribió:

You can export 2 PNGs one with grid to put GCPs on, and second PNG without grid, but exactly same size (in pixels).

And use GCPs put on first grid-equipped PNG to georeference second "grid-free" PNG.

Grid is used only to get pixel coordinates.

Dealing with pdf and 'reverse engineering' for me seems a bit complicated stuff,

since in addition to 6 georeference parameters, you need to deal with scale and so on,

so I'd rather used quick and dirty solution with grid and rasters.
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