MP format Zoom# parameter

[glendeni]

I noticed that some of my .mp files have
  Levels=4
  ...
  Zoom0=1
  Zoom1=2
  Zoom2=3
  Zoom3=4
whereas some others have
  Levels=5
  ...
  Zoom0=0
  Zoom1=1
  Zoom2=2
  Zoom3=3
  Zoom4=4
The history of those is lost to me so I was trying to understand what the "Zoom#="
parameter does.

Reading the cgpsmapper manual, "Level#=" and the difference between "Hardware" and "Map" zoom levels are thoroughly explained. But all I can find for "Zoom#=" is "Refer to Section 4.4" - yet that section discusses "Level#=" but nowhere mentions "Zoom#="!  There is a later use of
  Zoom0=0
  Zoom1=1
  ..
  Zoom4=4
in an example - but that it all I can find!

I'm surprised that this seems an omission from the otherwise remarkably detailed descriptions in the manual.  Does anyone know what "Zoom#=" is supposed to do? Might this be an obsoleted parameter?

Jack

[jolly47roger]

Hi Jack,

The Levels# directive links hardware levels (bits per coordinate like 21 or 23) to zoom levels.
For each object, the Data# directive defines the level at which the objects coordinates apply. My assumption is that the Zoom# directive maps the Data# to the Level#.

For example LevelX=21 ZoomX=Y DataY=(50.1,0.5) .

But, for safety, I keep X and Y the same so it's always, for example Zoom2=2

[glendeni]

Since I've been running a bazillion variant runs lately, so now have a relatively quick testing process, I decided to run a test of the "Zoom#=" parameter.  My test run compiles two different .mp file using mkgmap to create two separate .IMG files, then again uses mkgmap to combines those files into a gmapsupp file.  The first file always had Levels=5 with "Zoom0=0 ... Zoom4=4".  The second file always had Levels=4  with 2 cases (A) "Zoom0=0 ... Zoom3=3" and (B) "Zoom0=1 ... Zoom3=4".  I could not see any difference whatsoever between the two cases with differing Zoom# parameters.

Jack