<html><body name="Mail Message Editor"><div>Jan:</div><div><br></div><div>I think you can assume the projection is the Bonne. Flamsteed, as you note, is the sinusoidal. The sinusoidal is the Bonne with its standard parallel at the equator. Topographic mapping in France does refer to the Bonne as "modified Flamsteed". (See Hunt & Schott 1854, p. 98: "Tables for Projecting Maps, with Notes on Map Projection", from "Report to the Superintendent of the Coast Survey... 1853", Appendix 39. Washington D.C.: Robert Armstrong, Public Printer.)</div><div><br></div><div>Regards,</div><div>-- daan Strebe</div><div><br></div><br>On Nov 26, 2008, at 9:06:05 AM, "Jan Hartmann" <j.l.h.hartmann@uva.nl> wrote:<br><blockquote style="padding-left: 5px; margin-left: 5px; border-left-width: 2px; border-left-style: solid; border-left-color: blue; color: blue; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: -webkit-monospace; font-size: 11px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; ">This certainly makes a difference! Adding +nadgrids=@null to the<span class="Apple-converted-space"> </span><br>original definition gives a map with a 120m South shift, still too much<span class="Apple-converted-space"> </span><br>but nearing a solution. Isn't this a bug in PROJ? I did not request a<span class="Apple-converted-space"> </span><br>datum shift, and neither the from-projection, nor the to-projection had<span class="Apple-converted-space"> </span><br>a datum defined, only ellipsoids. I am using Proj 4.6.1.<br><br>I looked again at the 19th century documentation, and it says the map is<span class="Apple-converted-space"> </span><br>in the "modified Flamsteed or French" projection. All later<span class="Apple-converted-space"> </span><br>documentation refers to "Bonne" as the projection for this map and its<span class="Apple-converted-space"> </span><br>successors; they are actually still called "Bonne maps" here. The<span class="Apple-converted-space"> </span><br>Flamsteed projection is the classic sinusoidal projection, which is<span class="Apple-converted-space"> </span><br>certainly not the one for this map, and the "modified Flamsteed<span class="Apple-converted-space"> </span><br>projection" seems to be some sort of conic projection, but I haven't<span class="Apple-converted-space"> </span><br>found any information on this. It could be the same as the Bonne<span class="Apple-converted-space"> </span><br>projection, which is conic too. Does anyone have any information on this?<br><br>Jan<br></span></blockquote><br><div><br></div><div class="aol_ad_footer" id="u18EE738C648945BBA45FD1BBA319A2BF"></div></body></html>