Dear Eric,
I would include all the options you mentioned into the product (as long they
fit together) to keep the options as flexible as possible. Also there should
be corresponding MapBasic statements if they aren't already there.
Kind regards
Thomas G�lden
Diplom-Geologe
Email (privat): [EMAIL PROTECTED]
Email (dienstl.): [EMAIL PROTECTED]
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of
[EMAIL PROTECTED]
Sent: Tuesday, November 23, 1999 4:15 AM
To: Steve Wallace
Cc: MapInfo-L
Subject: MI Re: Problem discovered w/Bounds Clause
Thanks for posting this, Steve. As it so happens, a MapInfo partner
mentioned the same issue at the Partner Conference! To some folks, the
reason why this issue has not been addressed by 'bounding' the cosmetic
layer may not be completely obvious.
Currently, when the cosmetic layer is created, it is assigned a coordinate
system that is basically the same as that of the first layer in the map.
So, if you have a MapBasic or Workspace command that says:
Map from XXXX, YYYY, etc.
the cosmetic layer will have the same coordinate system as table XXXX!.
This is just a convention established long ago which creates a cosmetic
layer with a reasonable coordinate system and avoids having to prompt the
user for information that they might not know or care about. They might not
even use the cosmetic layer.
However, the coordinate system is unbounded because we have no idea if
people will want to add objects to this layer outside those bounds. I
guess having ones data truncated to the bounds seems worse than the
opposite behavior described by Steve.
One way we might improve this would be to add an optional cosmetic layer
coordinate system clause to the "Map" command. Whatever it specified would
be accepted outside of error conditions such as Non-earth and earth systems
mixing. This would free developers up from the caring about the first
table.
The second part of my idea would be to add a user preference specifying
some form of these same options for new Map Windows created. Perhaps
something as simple as a choice of bounding or unbounding the cosmetic
layer or possibly explicit preferences as to the coordinate system. whether
it is derived from the first table or not, etc. With some extra work, a
Set Map Layer Cosmetic command could even alter the system after creation
Your input is appreciated.
Eric Blasenheim
MapInfo Corporation
Steve Wallace <[EMAIL PROTECTED]> on 11/18/99 07:45:49 PM
To: MapInfo-L <[EMAIL PROTECTED]>
cc: (bcc: Eric Blasenheim/MapInfo Corp)
Subject: Problem discovered w/Bounds Clause
Something that might interest those of you who use the MapInfo "Bounds"
clause to increase the precision of your maps -- don't use the Cosmetic
Layer to transfer data around. I had been wondering why some of my
points/lines would move around from time to time. The distances were very
small, to the point where some might argue, "Why does it matter?" But the
problem is, the Object Processing notices these small differences, leaving
you will all kinds of unwanted spikes and slivers when you split or erase
objects.
The problem is that I, like many of you, use the Cosmetic Layer when
editing maps. In fact, when I first noticed the problem was going through
the prescribed method taught by MapInfo for fixing self-intersecting
polygon errors flagged by MapCheck. When I copied a string of nodes from my
bounded map to the cosmetic layer, then transformed to a region and went
back to process this against my original, the region in the cosmetic layer
was slightly offset from the original.
This is because the Cosmetic Layer is unbounded -- you lose any increased
precision from your bounded objects when you paste them info the cosmetic
layer.
WORK-AROUND: If you work with bounded data, create a blank layer with the
same bounds clause and use it like you would your cosmetic layer when you
need to put/process objects in a temporary layer.
This certainly explains why I have so many unwanted artifacts in my maps...
Steve Wallace
GIS & Market Information Manager
Florida Farm Bureau Insurance Companies
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