CaverBruce
commented
5 years ago To clarify, my assumption is always that true or grid north are very similar and are directly up the page, and that the declination (magnetic north) arrow is deflected to the right for a positive declination angle, along with the sketch and centreline.
From discussion in #49 Centreline and sketch should be rotated by the declination. Down here in NZ the declination is in excess of 20 degrees, so it makes a significant difference. It is not to do with variations in declination over time, in-cave software need not extend to such detail. The reason I want it rotated by the declination (a users rough estimate is sufficient) is so that the sketch and the finished output look roughly the same. ST needs to produce rotated exports as well of course. Much easier on the cartographers mental capacity, and it means that Therion drawing object -align statements for the likes of top, bottom, topleft etc are more likely to behave as expected. As I describe in the Therion wiki, you can also compensate for intentional rotation of the finished cartographed drawing, if you know in advance what orientation you will use. See the third bullet point under CAUTIONS about two thirds of the way down the page https://therion.speleo.sk/wiki/pockettopotherion?s[]=pockettopo&s[]=cautions and the notes under -align almost half way down this page https://therion.speleo.sk/wiki/drawingchecklist?s[]=rotate#points
As a visual prompt, it would be nice to have a magnetic north arrow on the bottom left of the plan sketch screen. This is because I have cave systems where the finished map has north up the page (declination = 20 deg) and systems where the finished map is rotated 70 degrees (fudged declination for in-cave software = 70+20 = 90 deg). In PocketTopo there is no visual que as to what is set, so i sometimes make mistakes. An arrow would help prevent user errors.