To Execute a Mosaic
This page presents
procedures to make a mosaic among projects or just copy data (lines, points, images etc) among ILs. In the lines case it is still possible
to make their own simplification.
The topics covered here
are:
See also:
Importing and Exporting Data.
How to create an IL
Maps vector edition.
Introduction to Mosaic
The mosaicking process can be defined as a fusion of different images into a
single image, corresponding to a geographical area defined (the image term is
understood here as maps in the raster and/or vector representations).
The mosaic term in Geographical Information Systems (GIS) is a synonym of
maps fusion, that is, separated maps, although adjacent, are automatically
grouped into a single map. The mosaicking final product is an image or a map
topologically consistent, with physical continuity (Bonhom - Later, 1994).
The figure below shows an example where two adjacent ILs becomes a mosaic. In
this version the SPRING only makes the mosaic based on the existing data
coordinates, such that the lines adjusting and the topology must be rebuilt
after the mosaicking.


Mosaic
Mosaicing using the Spring allows the user to change data, that is, information
layers, of different projects and also different projections, or even between a
single project (in this case there is a data copy function between ILs).
However, the mosaic option implemented satisfies the data changing need (ILs)
only inside of the same Data Base. In case the user wants to change
data among different data bases, it has to use the importing
and exporting resources.
In the mosaicking between equals information layers, all the representation can
be transferred from the source IL to the target IL. In case we have information
layers from different categories, not all or none of the representation can go
from an IL to another. For instance: an IL of the thematic category
(source) is only copied to an IL from the numeric category (target), the Lines
representation (L) and Points representation (P).
The table below shows which representations are transferred from an source IL to
a target.
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Destiny
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IMAGE
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THEMATIC
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NUMERICAL
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CADASTRAL
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NETWORKS
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IMAGE
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M/S/R/IC
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R
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-
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R
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-
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Source
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THEMATIC
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-
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L/P/C/I/Pol
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L/P
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L/P/Pol
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L
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NUMERICAL
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-
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A/LB/I
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A/G/Ti/I/LB
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A/I/LB
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A/I/LB
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CADASTRAL
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-
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L/P/Pol
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L/P
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L/P/O/Pol
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L
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NETWORKS
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-
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L
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L
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L
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L/O
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The representation codes presented in the above table are:
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Thematic IL: Points (P); Lines (L);
Images (I) - raster vectors formats; Classes (C) - associated polygons
to the classes; Polygons (Pol) - topology.
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Numeric IL: Samples (A) - spot
heights and original contour lines; Grid (G) - rectangular grid; TIN
(Ti) - "Triangular Irregular Network" , irregular triangular
grid; Contour lines (I) - contour lines generated from the grid, Broken
Lines (BL).
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Image IL - for the Image model the
mosaic between ILs of the image type: Mono (M) - monochromatic channel;
Synthetic Image (S); Labeled Image (R); Classified Image (IC) are
available.
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Network IL: Lines (L); Objects (O).
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Cadastral IL: Points (P); Lines (L);
Objects (O); Polygons (Pol).

Images Mosaicking
For the image mosaicking is fundamental that the images are georeferenced with
an approximate precision. The images can be in different projects or in GRIB
files that are not part of a project, in this second case it must have the
existence of control points associated to the file (see how import
a GRIB file - Images Register). Without the register there is no way to
mosaic images once there is no geographical reference associated.
The mosaic quality is directly associated to the images register precision when
in different projects.
NOTE: The mosaicking operation is performed considering as a target IL
the active IL in the "Control Panel", that is, the one receiving the
data coming from other ILs. See next how to execute a mosaic between images.
Executing a Mosaic between images:
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create an information layer (
) of the Image model (the IL receiving
the data) and activate it in the "Control Panel" ( ); or just activate an existing one;
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click on Edit
- Mosaic...
or Image - Mosaic... in the Main Menu;
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in the "Mosaic"
window, select in the Projects list the one which has the
source data. NOTE: it is possible to select even the active Project,
allowing to make a copy of the data among ILs from the same project;
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click on a Category from
the list. The categories presented are related only to the selected
Project above, in which there is at least an IL associated;
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click on a Source
Information Layer from the list. Notice that when an IL is of the Image
type and the target IL is also from the Image type the existing
representation are not presented. In this case the mosaic recognizes
automatically that it is an image in gray levels, color image
(synthetic), classified or labeled. In case the target IL supports the
vector representation (Thematic or Cadastral) and the source IL has a
labeled image it is possible to mosaic the lines and polygons for this
other IL.
-
click on the selection Mosaic
button to add data to the target IL. In case this button is not
activated a confirmation will be asked to remove the existing data. In
the case of the first time that it is applied to a new created IL, it is
not required to activate this button;
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click on Bounding
Box...
to select a source IL smaller area (see more information about the
window
"Bounding Box");
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click on Apply to
make the mosaic.
NOTE: Repeat the steps above for each IL to be inserted in the target IL.

Vector Data Mosaic
For the vector data Mosaic (thematic, numeric, cadastral and networks ILs)
the SPRING does not make any adjust in the contact lines between the two ILs
which will be glued side by side. In this way after making the mosaic the
boundaries between the imported ILs have to be checked and an editing work in
these points has to be executed.
The mosaic quality is directly associated to precision and scale of the original
data which are in projects in different ILs.
In this SPRING version it is possible to select the mosaicking option or copy all
from a source data to a target data, or copy only the selected contents,
indicating which lines from the source IL will be copied, or even, all the lines
inside a rectangle defined by the user. In this last case the lines
will be clipped at the rectangle boundaries, keeping only the rectangle
internal lines.
NOTE: The mosaicking operation is performed considering as target IL, the
one that is active in the "Control Panel", that is, the one which will
receive data coming from other ILs. See next how to execute a mosaicking
between vector data selecting lines or defining a rectangle area.
Executing a Mosaic for vector data copying:
-
create an information layer (
) using the same model that will receive
the data (Thematic, Numeric, Cadastral or Networks) and/or
activate an IL using the "Control Panel" ( );
-
click on Edit
- Mosaic...
in the Main Menu;
-
in the "Mosaic"
window, select, in the Projects list the project with the source
data;
-
click on a Category from
the list. The categories presented are related to the project selected
above, where there is at least one associated IL;
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click on a Source
Information Layer in the list. Notice that below this list, it is
presented the existing representations of the selected IL;
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select the representation you
want to make a mosaic or to copy;
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in Copy select
between Everything or Selected Contents. If the Selected Contents option was chosen it is possible to select only the
polygons, lines and points desired from the source IL. To select the
contents it will be presented the drawing window 5 with the selected
representation of the source IL to either copy or mosaic. When clicking
on the desired entities, these will be highlighted using the Cyan color.
When selecting a polygon, the polygon boundary lines are automatic
selected either to copy or to mosaic. Select as many entities as you
wish;
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click on the Mosaic
select button to add data to the target IL. If this button is disable it
will be asked to confirm the existing data removal;
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click on Apply to
perform the mosaicking or copying.
NOTE: Repeat the steps above for each IL which will be inserted in
the target IL.
The mosaicking operation using a rectangle follows the same procedure used with
images, just select the rectangle involving the interested area in the
"Bounding Box". Only the entities inside the rectangle will be used in the
mosaicking process.
NOTES:
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The ability of data
copying, mainly digitized lines and points between ILs of the same
category is useful when the user wants to make changes or simulations in
an IL, and having another one as a backup.
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The ability of data copying
between different categories is, sometimes, needed, when the user
created and digitized data mistakenly in a wrong category, the system
allows to copy these data to another IL in another category.
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Consider this practical
application example of line copying between IL of different categories:
starting from a numeric IL which has contour lines, it is possible to
generate an "Hypsometric" map (thematic category) by making
copies of these contour lines once the slicing heights are the contour
lines themselves. Otherwise, the user would have to generate a grid and
later slice it in the desired intervals. Notice though that doing it
from the contour lines themselves the slicing would be closer to the
reality.
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Selected Classes Button: when this button is
clicked only the entities in which the classes were previously selected
in the control panel will be copied to the other IL. Entities without a
class will be copied normally.

Simplification
Cartographical generalization can be understood as an observable geographical
space simplification such that it allows its representation in a map. In the
digital domain where geographical information systems technology is inserted,
the cartographical generalization has the major goal of a data base contents
universalizing according to a given objective. The process is scale dependent
of the data representation trying to reduce the complexity without loosing
spatial precision and, for the data attributes, which also have to take into
account the meaning of the map being considered and might give a more efficient
communication with the map user.
The geographical information systems normally have a cartographical
generalization tool available for the users, which is based on spatial
transformations changing the data representation in terms of geographical
localization ( simplification, smoothness, aggregation, exaggeration, and
displacement) and topological meaning (classification and symbolization).
As most of the objects use a line as a basic entity for their representation,
the line simplification has been studied frequently and it is the most
common transformation found in the existing systems. The line simplification
methods try to select and keep the points that characterized better the line
digital representation. A good redundancy example is to use a digitizer in the
continuous mode, which usually generates a line with a large number of points.
The figure below shows the line simplification purpose.

The SPRING system presents three algorithm options for line simplification:
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the original
Douglas-Peucker algorithm (Douglas and
Peucker, 1973);
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an adaptation of the
Douglas-Peucker algorithm using the area/perimeter ratio;
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an adaptation of the
Li-Openshaw algorithm (Li and Openshaw,
1992) accumulating the covered distances over each line.
When an IL of the Thematic, Cadastral or Networks
model has the lines representation, a simplification of them can be executed,
so the lines will have less points for the geographical entities contour
representation. See next how to do it.
Executing lines simplification:
-
create an information layer using
the same model as the data (Thematic, Numeric, Cadastral, or Networks)
and/or activate one in the "Control Panel";
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click on Edit
- Mosaic...
in the Main Menu;
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in the "Mosaic"
window, select the Projects list which has source vector data;
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click on a Category of
this list. The categories presented is related only to the selected
Project above, in which there is, at least, one associated IL. Only the
categories of the Thematic, Cadastral and Networks model can be
simplified;
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click on a Source
Information Layer in the list. Notice that below this list the existent
representation of the selected IL is presented;
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select in Lines
Representation.
Notice that the Simplification button is enable;
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click on Simplification;
and next on Simplification
Parameters... . The windows with the parameters is presented;
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after defining the
parameters above, it is required to define what will be simplified,
thus, in Copy, select between Everything or Selected Contents.
If the Selected Contents option is chosen, it is possible to select only
the source IL lines which will be simplified or the ones inside the
rectangle defined by the user. See the operation differences between
these two options:
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click on the Mosaic
selection button to add data into the target IL. If this button is not
enable it will be asked a confirmation to remove the existing data;
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click on Apply so
the data simplification will be executed.

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