External database links are most appropriately used when data is dynamic in nature. For example, a sewer pipe may have several instances of maintenance. This is an ideal situation in which to use an external database link. The object has a single key, which is related to a record in a database. The database application can then be used to relate this record to other tables that contain additional information.
Some of the common benefits of using external tables:
1. External data can be accessed by individuals without their having access to the drawing files.
2. External data is better for data that changes frequently, such as maintenance information.
3. Drawing file size is not increased if the data is stored externally.
When you drag and drop a database file into the AutoCAD Map 3D Explorer task pane to attach it to the drawing, a Universal Data Link (UDL) is automatically created. By default, it is stored in the folder called Data Links in the Application Data folder in the users Document and Settings folder.
Monday, December 1, 2008
AutoCAD Map 3D: Drawing Cleanup Guidelines
When performing drawing cleanup, consider the following issues:
If objects have object data, hyperlinks, or SQL links associated with them, drawing cleanup may break these associations. You can control this behavior by selecting a cleanup method that either retains or modifies the original object.
For greater control of the cleanup operation, consider performing one cleanup action at a time and completing one action before moving to another.
To display the extent and nature of the problems in the drawing, use markers for your first cleanup pass.
Start the cleanup operation using small tolerances and review to find out whether the tolerance setting has captured the errors. If the tolerance settings are too low, repeat the cleanup operation with a larger tolerance until the operation recognizes the errors. Be careful when increasing tolerances. If tolerances are set too high, valid geometry can be recognized as errors.
If objects have object data, hyperlinks, or SQL links associated with them, drawing cleanup may break these associations. You can control this behavior by selecting a cleanup method that either retains or modifies the original object.
For greater control of the cleanup operation, consider performing one cleanup action at a time and completing one action before moving to another.
To display the extent and nature of the problems in the drawing, use markers for your first cleanup pass.
Start the cleanup operation using small tolerances and review to find out whether the tolerance setting has captured the errors. If the tolerance settings are too low, repeat the cleanup operation with a larger tolerance until the operation recognizes the errors. Be careful when increasing tolerances. If tolerances are set too high, valid geometry can be recognized as errors.
AutoCAD Map 3D: Drawing Cleanup Strategies
Drawing cleanup is not a single operation in which you remove all errors in the drawing. Depending on the number and type of errors, drawing cleanup is an interactive process in which you clean certain errors and then repeat the process to clean additional errors.
The reason for cleaning a drawing can influence how you approach the cleanup. For example, if you intend to use the drawing for a street network topology, then crossing objects can be tolerated and may even be desirable. However, if you intend to use the drawing to produce a polygon topology, crossing objects cannot be tolerated. You also need to consider any object data or SQL links that are attached to objects in the drawing. Using incorrect methods of cleanup may destroy these links.
The reason for cleaning a drawing can influence how you approach the cleanup. For example, if you intend to use the drawing for a street network topology, then crossing objects can be tolerated and may even be desirable. However, if you intend to use the drawing to produce a polygon topology, crossing objects cannot be tolerated. You also need to consider any object data or SQL links that are attached to objects in the drawing. Using incorrect methods of cleanup may destroy these links.
AutoCAD Map 3D: Drawing Cleanup
Errors can be introduced into maps in several ways – for example, while digitizing or through inaccurate scanning. You must address errors by using the drawing cleanup tools before you can create topology or perform map analysis. AutoCAD Map 3D has several tools to help you clean up and edit your maps so that they are accurate and suitable for topology, mapping, and plotting.
You can manually clean geometry in a map by using standard AutoCAD editing tools. However, most maps are so extensive and complicated that using manual editing techniques is not only tedious, but is also unlikely to identify every error that needs o be addressed.
The drawing cleanup tools in AutoCAD Map 3D automate many map editing tasks.
You can manually clean geometry in a map by using standard AutoCAD editing tools. However, most maps are so extensive and complicated that using manual editing techniques is not only tedious, but is also unlikely to identify every error that needs o be addressed.
The drawing cleanup tools in AutoCAD Map 3D automate many map editing tasks.
AutoCAD Map 3D: Deciding When to Use Object Data
Object Data is available only to AutoCAD Map 3D users. Mapping systems may be designed to separate database functions from the graphic map, usually when the data is accessed and updated regularly.
Object Data is best used to document static data that is associated with an object, such as a sewer pipe diameter, type, length, and so on. This data does not require regular access by non-AutoCAD Map 3D users. Dynamic data, such as maintenance records, often requires multiple records to associated to a single object. Object data becomes cumbersome when more than one record in the same table is linked to a single object. Many functions, such as a query, thematic maps, and the properties palette, recognize only one record per object, regardless of how many are associated with the object.
Object Data is best used to document static data that is associated with an object, such as a sewer pipe diameter, type, length, and so on. This data does not require regular access by non-AutoCAD Map 3D users. Dynamic data, such as maintenance records, often requires multiple records to associated to a single object. Object data becomes cumbersome when more than one record in the same table is linked to a single object. Many functions, such as a query, thematic maps, and the properties palette, recognize only one record per object, regardless of how many are associated with the object.
AutoCAD Map 3D: The Power of Object Data
Object data is an easy and flexible method of attaching tabular data to objects in AutoCAD Map 3D.
After acquiring or creating map geometry and objects’, the next step is to associate data with those objects. Other than land features, such as contour lines, nearly every object in a map has underlying data that describes or controls the objects attributes, in addition to its location and object type. Examples include fire hydrants with physical attributes and maintenance records, and streets with speed limits and maintenance records. The underlying data, and how it is used or displayed, provides a rich and sophisticated environment for the analysis, display, and reporting of a digital representation of your mapping project.
You can think of object data as block attributes, except you are not limited to attaching the Object Data to a block reference. You can create Object Data tables and attach them to AutoCAD objects for many purposes. AutoCAD Map 3D generates Object Data automatically to store topology information and store information when you move data into and out of AutoCAD Map 3D. For example, when importing data from other file formats, tabular data is imported and associated to AutoCAD objects as Object Data.
After acquiring or creating map geometry and objects’, the next step is to associate data with those objects. Other than land features, such as contour lines, nearly every object in a map has underlying data that describes or controls the objects attributes, in addition to its location and object type. Examples include fire hydrants with physical attributes and maintenance records, and streets with speed limits and maintenance records. The underlying data, and how it is used or displayed, provides a rich and sophisticated environment for the analysis, display, and reporting of a digital representation of your mapping project.
You can think of object data as block attributes, except you are not limited to attaching the Object Data to a block reference. You can create Object Data tables and attach them to AutoCAD objects for many purposes. AutoCAD Map 3D generates Object Data automatically to store topology information and store information when you move data into and out of AutoCAD Map 3D. For example, when importing data from other file formats, tabular data is imported and associated to AutoCAD objects as Object Data.
AutoCAD Map 3D: Rubber Sheeting a Drawing with No Coordinate System
What happens when you get a drawing file with no coordinate system and you need to align it to your existing map? This is where the Rubber Sheet command comes in handy.
Rubber sheeting is a nonuniform adjustment of a data set based on the movement of known control points to new locations. For example, data collected by aerial survey may be inaccurate because of flight alignment and camera inaccuracies. By comparing this data with accurate ground survey data, the aerial data can be stretched or rubber sheeted over the accurate data using control points and monuments common to both data sets.
Use rubber sheeting when you want two or more different data sets from different sources to align geographically: for example, when stretching a new subdivision map into a preexisting parcel map.
Rubber sheeting is a nonuniform adjustment of a data set based on the movement of known control points to new locations. For example, data collected by aerial survey may be inaccurate because of flight alignment and camera inaccuracies. By comparing this data with accurate ground survey data, the aerial data can be stretched or rubber sheeted over the accurate data using control points and monuments common to both data sets.
Use rubber sheeting when you want two or more different data sets from different sources to align geographically: for example, when stretching a new subdivision map into a preexisting parcel map.
The reference map is correct, but the map with new details is severely distorted. By running the Rubber Sheeting command and selecting common control points, the two maps can be correctly aligned.
Objects that have a given shape, such as circles, arcs, and ellipses, retain their original shape.
Warning: Use rubber sheeting only when absolutely necessary because it can severely compromise the accuracy of your data.
Because rubber sheeting is not a linear transformation, it is difficult to reverse the effects of the transformation and return a drawing to its original state. You should save your drawing before you perform a rubber sheeting operation.
AutoCAD Map 3D: Analyzing Geospatial Data
Many AutoCAD Map 3D users do not have a need to do much geospatial analysis, and so analysis tasks are often left to specialists. However, there are a few types of analysis that most users perform fairly frequently. The most common of these tasks is to create a thematic map. Most geospatial analysis involves creating a thematic map of some kind. Whether you are interested in the property values of a set of parcels, crime statistics in a neighborhood, or the year of installation of telephone poles, the workflow is very similar in all cases. You query spatial data and attribute data from the same source or from multiple sources, and then use the values of the attribute data to change the display characteristics of your map. The thematic map that results from this process gives you new information, allowing you to see patterns or trends that would not be visible in any other way.
AutoCAD Map 3D has always had powerful query tools for working with the content of DWG files. The addition of FDO providers has extended the scope of those tools and made a much wider range of data available for query directly into the program. You can use complex spatial queries with location-based criteria or SQL statements to find exactly the data you want from the data source. The styling and theming functions of Display Manager in AutoCAD Map 3D have been redesigned to make them easier to use and more flexible. If you are creating thematic maps for distribution over an intranet or on the Internet, you can publish maps directly to MapGuide Enterprise or MapGuide Open Source. A web page and the tools to interact with the map are generated for you automatically.
AutoCAD Map 3D has always had powerful query tools for working with the content of DWG files. The addition of FDO providers has extended the scope of those tools and made a much wider range of data available for query directly into the program. You can use complex spatial queries with location-based criteria or SQL statements to find exactly the data you want from the data source. The styling and theming functions of Display Manager in AutoCAD Map 3D have been redesigned to make them easier to use and more flexible. If you are creating thematic maps for distribution over an intranet or on the Internet, you can publish maps directly to MapGuide Enterprise or MapGuide Open Source. A web page and the tools to interact with the map are generated for you automatically.
AutoCAD Map 3D: Handling Styles and Labels
Features such as roads, parcels, or poles are generally stored in a database or data store as raw geometry; that is, they are simply georeferenced lines, polygons, and points (although they also have a non-spatial aspect, which consists of associated attribute data). When you want to create a compelling map for publishing, you will almost always want to style the raw feature data in some way. Styling is the process of assigning display characteristics (such as line color, line pattern, fill color, fill pattern, and so on) to the feature. In AutoCAD Map 3D, the style is applied to the layer and is stored as part of the layer definition. The underlying feature data is not changed in any way.
You can save a lot of time by sharing layer styles that have already been defined by other users for their maps and reusing them in your own maps. See the first workflow in this section for an example of how this process works.
Another aspect of styling is theming, which is the process of styling maps according to an attribute value, for example, creating a theme that colors polygons representing districts according to their population.
You can style or theme maps in AutoCAD Map 3D and then use Autodesk MapGuide Enterprise or MapGuide Open Source to distribute those maps across your enterprise or externally on the Internet. MapGuide recognizes the styles and themes that you created in AutoCAD Map 3D; therefore, you do not need to reapply them when you want to publish your work to a wider audience. Because AutoCAD Map 3D and MapGuide use the same FDO providers to access features sources, when either program accesses those features in a layer that has styles defined for it, the layer appears with the correct styling and theming. This allows you to create Web-based applications in which edits to the central data are automatically reflected in MapGuide and become immediately available to users of the MapGuide application.
You can save a lot of time by sharing layer styles that have already been defined by other users for their maps and reusing them in your own maps. See the first workflow in this section for an example of how this process works.
Another aspect of styling is theming, which is the process of styling maps according to an attribute value, for example, creating a theme that colors polygons representing districts according to their population.
You can style or theme maps in AutoCAD Map 3D and then use Autodesk MapGuide Enterprise or MapGuide Open Source to distribute those maps across your enterprise or externally on the Internet. MapGuide recognizes the styles and themes that you created in AutoCAD Map 3D; therefore, you do not need to reapply them when you want to publish your work to a wider audience. Because AutoCAD Map 3D and MapGuide use the same FDO providers to access features sources, when either program accesses those features in a layer that has styles defined for it, the layer appears with the correct styling and theming. This allows you to create Web-based applications in which edits to the central data are automatically reflected in MapGuide and become immediately available to users of the MapGuide application.
AutoCAD Map 3D: What is FDO?
FDO Data Access Technology is Autodesk’s common geospatial data access platform. FDO is incorporated into Autodesk Geospatial products, and is also available as a standalone, open source technology for developers. FDO supports the creation of data-store neutral applications and makes it easier to exchange information. The underlying technology is based on open standards, so it eliminates many of the difficulties commonly encountered when working with proprietary systems. Using FDO Providers, you can connect directly to ESRI ArcSDE and SHP, Oracle, Microsoft SQL Server and MySQL feature sources, as well as access public data sources via WMS and WFS. You can also access data providers developed by the open-source community using FDO. The result is that you can build a map using layers of data from many different sources, while accessing all of those data sources in exactly the same way.
All FDO providers access data stored in data tables using standard database concepts. An FDO feature source is any source of feature data that can be accessed using an FDO provider. It can be a file, such as SDF or SHP, a relational database, such as Microsoft SQL Server, or it can be middleware, such as ArcSDE. These feature sources can contain a single feature type, such as parcels, or they may contain a complex data model with multiple features and attribute tables.
When you organize and classify your data, and use FDO Data Access Technology, you can work with much larger data sets than you can with traditional DWG files. Classifying data and storing it in an FDO feature source also gives you more flexibility when styling your data, allowing you to move beyond basic CAD maps to advanced cartography and presentations. In a DWG file, style is a property of the AutoCAD object. However, data stored in an FDO feature source does not have any styling. Styling is separate from the data. This means you can use the powerful style engine, shared by AutoCAD Map 3D and MapGuide, to create different maps with different representations of the same data. For example, you can reorganize layers, change colors, use transparency, and theme features based on their attribute data.
All FDO providers access data stored in data tables using standard database concepts. An FDO feature source is any source of feature data that can be accessed using an FDO provider. It can be a file, such as SDF or SHP, a relational database, such as Microsoft SQL Server, or it can be middleware, such as ArcSDE. These feature sources can contain a single feature type, such as parcels, or they may contain a complex data model with multiple features and attribute tables.
When you organize and classify your data, and use FDO Data Access Technology, you can work with much larger data sets than you can with traditional DWG files. Classifying data and storing it in an FDO feature source also gives you more flexibility when styling your data, allowing you to move beyond basic CAD maps to advanced cartography and presentations. In a DWG file, style is a property of the AutoCAD object. However, data stored in an FDO feature source does not have any styling. Styling is separate from the data. This means you can use the powerful style engine, shared by AutoCAD Map 3D and MapGuide, to create different maps with different representations of the same data. For example, you can reorganize layers, change colors, use transparency, and theme features based on their attribute data.
AutoCAD Map 3D: FDO Overview
AutoCAD Map 3D provides data-access and data-management tools to make the process of integrating different types of data easier. In particular, FDO data providers and a consistent data-connect interface simplifies access and management of multiple feature sources. With AutoCAD Map 3D, you can extend your existing workflows and take advantage of efficiencies created through geospatial tools and store some of your information in a spatial data store, such as SDF. Also, you can augment your maps (DWG or other) by bringing in data from a variety of formats, including free data sources, such as web services (WMS and WFS).
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