Differences beween OO Mapper and the smart software for cartography

[lpechacek]

Looking at the pull request queue, I spotted the one for the rotation locked objects. That reminded me that I know about a few conceptual differences between Mapper and the other software that more or less sets the standard. Let me document my knowledge here and feel free to drop your knowledge bits here if you like. I expect to edit the first comment to collect all the bits in one place and maybe add illustrations.

I'm by no means suggesting that OO Mapper should go in certain direction. I'm personally against making Mapper a (free) copy of the other software. Still there are people working with both tools and trying to transfer maps between them. I'm hoping to provide explanation for the effects that they might encounter during map conversion.

Corner points and dash points

Mapper only has dash points. The other software had only corner points and added dash points in its version 8. Corner point is technically a cut in the line. A reset to the dash distribution algorithm. That means there are full-length dashes on both sides from a corner point. If the line has mid-symbols, they are placed away from the corner point.

A dash point, however, marks a center of a dash. A mid-symbol is placed at the dash point. Trying to tune dashes on a ruined fence with dash symbols is a real pain.

Interestingly enough, the smart software is smart enough to interpret dash points as corner points on dashed lines with mid-symbols. Convenience rules.

Half length dashes at line ends

The other software allows the line ends to be dash points. That halves the length of the end dashes, making it possible to create neatly looking path crossings. Mapper ignores the dash point flag on line ends, making dashes full-length there.

At least one symbol

If line is too short to place a mid-symbol, Mapper forces mid symbol on every line segment between the dash points. The other software, however, interprets the "at least one" for the whole line. So, for short lines, it places the mid-symbol on the longest segment of the line, and the condition is satisfied.

Closed loops

Mapper has closed loops, which is super cool. That means, the line end is indistinguishable form its beginning and a potential dash is placed at the gluing point. Internally it's done as half-length dashes at the line ends. However, these lines are exported without this elegant gluing. Watch out.

Symbol orientation to north

ISOM says that some objects/symbols are always orientated to the north. Common sense would dictate that such objects cannot be rotated in the map. Practice shows otherwise. The smart software allows rotation of all symbols, regardless of what ISOM says. Mapper, however, follows the standard and common sense and does not allow rotation on objects like a fodder rack, tower, undergrowth or marsh.

The trouble may come when rotated objects are imported from the smart software file format.

Side line cut and virtual gaps

The smart software allows double lines. Lines drawn with an offset from the carrying center line. There can be at most two side lines - left and right - and the file format has marks placed where the side lines should be cut. Mapper supports the side lines as border lines but does not have the marks for cutting.

Another evolutionary step in the other software was introduction of so called virtual gaps. The mechanism is the same - addition of a mark that says that neither the side lines nor the center line should be drawn beyond given point. With that we've got the types of marks - don't draw left line, don't draw right line, don't draw any line. Mapper does not implement any of these.

Text alignment

Text objects can be aligned horizontally and vertically to center, left or right. Mapper does this per object. That is, Mapper remembers for every text how it should be aligned. The symbol defined the font and other text properties.

The smart software defines text alignment in the symbol definition. That is, all text objects with the same symbol are aligned identically. So, when Mapper exports text to the smart format, it has to create multiple symbol definitions for the various text alignment it encounters in the map. So, if there is one text symbol (say Arial, 10 pt, blue) and there are two test objects, one aligned to the right, one to the left, the exported .ocd file will have two text symbols - one for the right alignment and one for the left alignment.

Graphic and layout objects

The smart software could convert map objects to so called "graphics". That is, the object is exploded to the elements like earth bank becomes the main line and tag lines, wall becomes the main line and dots. As part of the process new symbols are defined for the lines - just their width and color and nothing else. The next evolutionary step in the format development was creation of the graphic objects. Object conversion to graphics no longer creates the specialized symbols but rather records the line width and color in the object record itself. The idea itself is not bad, even if it violates the principle of unique object identity. All the map objects have their semantic expressed by the symbol assignment. Except the graphic objects which are just anonymous colored lines without further meaning. All fine as long as they are part of the map layout graphics but I've seen them in the map itself. Not nice.

The next evolutionary step are layout objects. They are graphic objects with arbitrary color. Graphic objects are bound to the map colors. Layout objects can be also raster images (logos et al.). Newest format versions can store the images in the .ocd file itself. I prefer the QGIS/ArcGIS approach where the map layout is separate from the map drawing.

Knockout is not overprint

Mapper has the color "knockout" property. When set, the color erases all underlying spot colors. When unset the color blends with the underlying spot colors.

The smart software has the overprint flag set on some colors. That, however is not the same as the Mapper knockout. The overprint affects PDF/EPS/AI and CMYK color separations but does not display on screen. The Mapper knockout effect is achieved by setting the spot color percentages to zero.

Mapper exports its knockout color property as the .ocd overprint property. That's wrong but it's a small issue given that spot color printing is now discouraged.

[dg0yt]

The pattern rotation thing is a bug and top on my list.

The line symbol things deserve a Line Symbol 2.0. (What is missing on your list: complex mangling between line symbols and combined symbols.) This is stuff for a new major version.

[dl3sdo]

@lpechacek: thank you for providing this overview.
I was about to add more 'differences' when I noted that this discussion is about differences of existing features and not about yet missing features.

[jmacura]

Thanks Libor for this thorough overview!
Regarding the "symbol orientation to north", note that the north does not have to be aligned with the upper paper side. Not rotating the objects is an error in such a case.