[Tagging] New rag to draw node name with rotate angle

Kevin Kenny kevin.b.kenny at gmail.com
Fri Nov 9 18:09:06 UTC 2018


‪On Fri, Nov 9, 2018 at 12:06 PM ‫دار الآثار للنشر والتوزيع-صنعاء Dar
Alathar-Yemen‬‎ <hubaishan at outlook.com> wrote:‬

> I suggest new tag to tell map render to draw the node name with a
> specified rotate angle not horizontal. We need this for some seas like Red
> Sea, and Suez Gulf in Egypt.
>

I have serious doubts whether encoding the rendering in the map in such a
way is a good idea.

A renderer that wished to label an area with an angled label could readily
determine the angle for itself, by computing the principal axes of the
area, and if its eccentricity exceeds a specified value, rotating the label
to align with the major axis.

An even better rendering could be achieved by computing the morphological
skeleton of the area, and placing the label along some smooth curve that
approximates the medial axis.

There are also algorithms that handle curved label placement in the
presence of interfering labels, although they are somewhat less well
developed. One such is described in Mathieu BARRAULT, "A methodology for
placement and evaluation of area map labels." _Computers, Environment and
Urban Systems_ 25 (2001), pp. 33-52.
http://geoinformatics.ntua.gr/courses/admcarto/lecture_notes/name_placement/bibliography/barrault_2001.pdf

Barrault describes the process of choosing a family of circular arcs that
well approximate the general contour of an area feature. Figure 3 of the
paper is informative about what criteria his heuristic takes into account
for 'goodness' of placement. Figures 10 and 11 show what the algorithm
achieves on sample elongated figures and Figures 13-14 show what it can do
in the presence of interfering labels.

To place this task on the mapper forecloses on the possibility that a
renderer can do it better.
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