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Project segmentation and merging

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Any big project involves, first of all, splitting a complex task into smaller ones. If you take a project digitizing large territory, the division into small plots and subsequent digitization is obvious. The problems start when one try to put the pieces together, and this need more detailed discussion.

Project segmentation and its reverse operation - joining of vector segments (subProjects) - are always mentioned at technology discussion for large Projects.

Segmentation is the most convenient way to influence upon duration of the work - if the Project is urgent, divide it in more subProjects and recruit more operators. Besides, segmentation guarantees identity of layer lists and other settings in all your subProjects.

Sometimes, it is the only way to avoid "tyranny of quantity" - significant slowing down of topology check-up and other operations in Projects containing tens of images and innumerable vector entities.

It is possible, of course, to create a number of Prototype-based Projects (actually, that was the method we applied before), but now there are far more effective tools...

SubProject creation based on the complete cover

The complete cover in Easy Trace is a Project containing all images to be vectorized. Linkage of all the rasters into the complete cover ensures correct positioning of every map sheet and helps at planning of further work because it is reasonable to make subProjects of about equal loading. Besides, subProject making out of adjoining map sheets lets you avoid merging of objects dissected by the borders.

Another advantage of segmentation is the ability "to glance over the horizon". The Create SubProject utility automatically encircles every subProject with a "borderland" consisting of narrow fragments of adjacent images - you will not puzzle over fragments of objects cut by the border. Besides, it helps to grade discrepancies at borders even before joining of subProjects.

The Create SubProject utility of Easy Trace Pro executes the following operations:

  • prepares subProject's raster cover circled by fragments of other rasters;
  • generates a frame at the subProject's border or around the images linked to the subProject;
  • draws subProject's borders in the initial Project (complete cover) and marks the names of raster files linked to the subProject;
  • copies the structure of the initial Project into the new-created subProject. The structure includes the layer list, attributive tables, domains of possible values of the attributes, tracing strategies, topology verification strategies, and so on.

As a result, a new folder will be generated that contains all the necessary elements of the subProject. The folder is absolutely independent from the initial Project - it may be transferred to another computer for autonomous Processing. At that, Processing results are FOR SURE compatible with the initial Project.

Suppose, we have the complete raster field. Act as following:

  1. Open the initial Project (complete cover).
  2. Select the command Utilities->Create SubProject.
  3. In the Project field, specify the images you want to include into the subProject with the mouse left button. To deselect a raster, click it once again.
  4. Specify the following parameters in the Create SubProject dialog box:
    • Name -input the name of the new-created subProject (no default name is Provided). If your subProject contains only one raster file, it is convenient to give it the same name. To remember the name of the image, navigate the cursor upon it - you will see its name in the pop-up window.
    • Folder - specify where you want to store this subProject (and maybe others). All the next subProjects will be saved to the same place - each of them in its own folder called by its name. If no name is specified in the Folder field, all the subProjects will be saved to the folder of the initial Project.
    • The utility may generate frames of the subProject and/or its images. Tick the desirable option and specify the layer of the frames (the set of layers is inherited from the initial Project).
    • The new-created subProject is always surrounded with a "borderland" - fragments of adjacent images. The width of margins (in Project units). may be specified in the corresponding field.
    • Different colors of subProject's images and their surrounding margins help to avoid unintentional "crossing of the frontier" at vectorizing. Select the color of the main raster (within the subProject) and margin rasters (around the main raster fields). Color selection is Provided for black-and-white rasters only.
    • Rasters belonging to individual subProjects may be marked on the complete raster field. Tick the Generate subProject frame option and specify the layer of the frame. Select the Generate raster name texts option and specify text height and layer - the inscription will be placed above every image included in the subProject.
  5. Click the Generate button (inaccessible before selection of images and input of subProject name) to complete the operation. You may start forming of the next subProject.

Joining of vector data

Joining of vector data is necessary at assembling of a united vector cover out of individual Projects or Project segments (subProjects). Usually it implies resolution of many small conflicts at borders of adjacent sheets, first of all - coordinate noncoincidence (considerable sometimes!) of polyline ends or polygon borders that must be united. Besides, object layers, line widths, Z-values and attributive data may mismatch.

Thus, "sewing together" of objects consists of the following operations:

  • to gather all the vector data that must be joined into one Project;
  • to specify boundaries that cut vector objects;
  • to join automatically non-conflict vector objects along the boundaries;
  • to mark conflict objects and to indicate the reason of joining inhibition;
  • to consider every remaining conflict and solve the Problem manually.

Easy Trace may join vector data along any vector line. This line (lines) will be considered as a boundary between objects that must be joined. It is reasonable that these lines must differ somehow from other vector data. To Provide the difference, attribute them to an individual vector layer. You should specify this layer in the field Bounds on layer and do not place any other polyline on this layer.

Vector data gathering into one Project can be done by import of subProjects. Scale and DPI of all imported data will be bring to conformity with ones of the target subProject.

Next step - specifying of boundaries. We have frames around subProjects of course, but usually they are badly "spoilt" by common vertices with snapped vector objects. That's why the boundaries where objects will be "sewed together" must be generated anew.

To do it, act as following:

  1. Open the first subProject (or maybe the initial complete Project).
  2. Import other Project segments (subProjects) - File->Import. Generate boundaries for joining at the same time with the help of the Layer that will contain the bounds option (if you specify a name of a non-existent layer, it will be generated automatically. Anyway it must contain nothing but the boundaries).
  3. After import, check position of the boundaries and correct it if necessary.
  4. Select the command Utilities->Polyline Joining. Specify in the corresponding dialog box:
    • layers that will be affected by joining;
    • layer of the boundaries;
    • snap radius - permissible distance between ends of the lines that can be joined;
    • conditions of line joining and checkup criteria.
  5. Correct all the mistakes applying the Editor .

Note: joining boundary may be drawn manually. It enables solution of non-typical tasks - for example, map joining by the border of adjacent administrative districts.

P.S. If you assemble the complete polygonal cover, remember that its topology verification slows down significantly after a certain number of polygons. It may be reasonable to combine subProjects into enlarged blocks first, check their polygon covers, then assemble the entire Project, start final verification ... and go for a weekend.

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