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.

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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.

 

 

 

Destiny

 

 

 

 

 

IMAGE

THEMATIC

NUMERICAL

CADASTRAL

NETWORKS

 

IMAGE

M/S/R/IC

R

-

R

-

Source

THEMATIC

-

L/P/C/I/Pol

L/P

L/P/Pol

L

 

NUMERICAL

-

A/LB/I

A/G/Ti/I/LB

A/I/LB

A/I/LB

 

CADASTRAL

-

L/P/Pol

L/P

L/P/O/Pol

L

 

NETWORKS

-

L

L

L

L/O


The representation codes presented in the above table are:

  • Thematic IL: Points (P); Lines (L); Images (I) - raster vectors formats; Classes (C) - associated polygons to the classes; Polygons (Pol) - topology.
  • 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).
  • 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.
  • Network IL: Lines (L); Objects (O).
  • Cadastral IL: Points (P); Lines (L); Objects (O); Polygons (Pol).

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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:

  • create an information layer ( atalho_pi.gif - 949 Bytes) of the Image model (the IL receiving the data) and activate it in the "Control Panel" ( atalho_painel.gif - 967 Bytes); or just activate an existing one;
  • click on Edit - Mosaic... or Image - Mosaic... in the Main Menu;
  • 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;
  • 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;
  • 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;
  • click on Bounding Box... to select a source IL smaller area (see more information about the window "Bounding Box");
  • click on Apply to make the mosaic.

NOTE: Repeat the steps above for each IL to be inserted in the target IL.

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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 ( atalho_pi.gif - 949 Bytes) using the same model that will receive the data (Thematic, Numeric, Cadastral or Networks) and/or activate an IL using the "Control Panel" ( atalho_painel.gif - 967 Bytes);
  • 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;
  • click on a Source Information Layer in the list. Notice that below this list, it is presented the existing representations of the selected IL;
  • select the representation you want to make a mosaic or to copy;
  • 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;
  • 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;
  • 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:

  • 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.
  • 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.
  • 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.
  • 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.

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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.

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The SPRING system presents three algorithm options for line simplification:

  1. the original Douglas-Peucker algorithm (Douglas and Peucker, 1973);
  2. an adaptation of the Douglas-Peucker algorithm using the area/perimeter ratio;
  3. 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";
  • click on Edit - Mosaic... in the Main Menu;
  • in the "Mosaic" window, select the Projects list which has source vector data;
  • 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;
  • click on a Source Information Layer in the list. Notice that below this list the existent representation of the selected IL is presented;
  • select in Lines Representation. Notice that the Simplification button is enable;
  • click on Simplification; and next on Simplification Parameters... . The windows with the parameters is presented;
  • 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:
  • 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;
  • click on Apply so the data simplification will be executed.