Semantic Translation Part 8/8: Round Trip
As the last post in this eight part series I don't want you to think in anyway that this has been an attempt at an exhaustive discussion of the topic. Arguably every post to this blog may touch on some aspect of semantic translation. Rather, I hope this can be a springboard for further discussions and feedback to delve deeper into concepts introduced here, or ones that I've overlooked.Often times I may phrase these concepts with examples of CAD to GIS translation, but equally valid is the need for GIS data to be accessible in a CAD format. Many times the same GIS database and spatial tools can be used to manipulate GIS data that is used to build CAD files. Translation between GIS and CAD needs to be bi-directional. ArcGIS tools like the EXPORT TO CAD tool may only be the last tool in a simple or complex model that prepares data to become the most useful expression of GIS data in a CAD file. This GIS data preparation may involve the creation of additional text annotation, symbology definition and the modification of geometric definitions. For example drawing polygons in a CAD file with non-redundant linear network of polylines rather than a closed polygons. Either is valid, but your CAD standards may require one or the other.
Just like you can use database look-up tables to match CAD symbology to GIS attributes you can use database look-up tables and other database concepts like query and CALCULATE to control CAD symbology based on GIS attributes. The ArcGIS-ArcInfo EXPORT TO CAD tool will take field values in specially named columns of the input GIS data and use the information to drive the CAD entity creation; columns like color, layer, thickness, CADType, DOCPath, etc... The EXPORT TO CAD tool can append to existing drawings, output to multiple drawings, overwrite drawings and create CAD entities from all different forms of GIS data.
Taking advantages of these round-trip capabilities your organization can standardize workflows where not only does data flow back and forth to critical applications, it flows more smoothly. Making subtle changes in data constructs or workflow procedures can greatly enhance the ease at which the translation of these spatial languages occurs. Defining, and more importantly implementing a well-defined CAD standard is perhaps the single greatest productivity enhancement step you can make to improve CAD and GIS interoperability. In situations where data flows from one organization or department to another, extra work to define submittal standards may be worth the effort or worth paying extra for.
In the comment section below this or any post I'd love to hear from you and what you would like to discuss in future posts.
posted by Don Kuehne at 1:15 PM
4 Comments:
I work for a GIS consulting firm and many of the concepts you bring up we address every day. My firm has had good luck converting existing CAD data to geodatabase format. In addition, we work with our clients to devise processes to export their geodatabase information back to CAD format for those existing CAD users.
Exporting linework has proven to be successful, but there seems to be some limitations in exporting geodatabase annotation to CAD text. Using export to CAD, without the designated CAD fields, the CAD text explodes and/or shifts.
I'm assuming that there is a way to export geodatabase annotation back to CAD so that the text does not shift or explode, so to speak. However, identifying the correct sequence of events to make this translation work has been frustrating.
Based on your experience, is there a process devised to properly export annotation to text...without any shifting or exploding of text?
Many times, clients will only convert to the geodatabase format if they know that there is a solid way to export the data back to CAD for their long-time CAD users.
Very interesting posts...thank you for your time.
CKS
One of the major CAD components of the next release of ArcGIS will address Text and Annotation. In the current ArcGIS version, some forms of annotation, like stacked text are not supported. There are also some known issues with text placement in general.
Don,
Your blog has been of immense help in understanding the key concepts and logic between different functionalities of CAD and GIS. I have worked with ArcGIS in the 'application' format, where i had all my data and database ready to use and had to simply run the required processes/tools for projects at hand. Recently I moved back to India and started working with an organization which is setting up its database from scratch. In the absence of usable data we are using primary data collected by different agencies and bringing it in GIS. The challenge has been bringing CAD data to GIS (currently being done without georeferencing)
While most ArcGIS 'help' sections have been helpful in giving a broad picture, I have been at loss to understand the exact sequence of steps to be taken. I would appreciate if you could provide your input to my understanding of the process as lined below -
1. creating a custom projection file for unaligned CAD data (which is created in local coordinates)
2. Using 'Import from CAD' tool, bring the CAD data to geodatabase in the required layers/feature classes
3.use the 'spatial adjustment' toolbar to align vector data
4.set the spatial reference for the imported data
5. Project data(?)
I tried using the georeferencing toolbar to create world files to align data in the right place, but faced 'scaling' issues and couldn't get to align the data exactly. Also, I have around 500-odd CAD files of neighborhoods, and all need to be placed in the same city bounds. Besides using model builder to create a standard import process, can i also use it to geo-reference all CAD files based on a standard system of conversion? or would i need to bring in each CAD file separately and spatially adjust it?
Anu,
Thanks for your comments.
1. Different than a world file that applies a transformation to the coordinates as a offset, scale and rotation, a custom projection defines a coordinate system for an area that ties it to the globe. Custom projections are possible by modifying the text in a .PRJ file. This text is in the Well Known Text format(WKT). How to modify this information is beyond the scope of this blog. (me)
2. Do not use the IMPORT FROM CAD tool. It is obsolete. Just use the feature classes in the blue folder icon that represents the CAD file. In the future you need to consider how ArcGIS for AutoCAD and MSD feature classes will affect your and everyone elese workflows if you are using AutoCAD for CAD and ArcGIS for GIS work.
3. You have to convert the CAD data to a geodatabase before you can use the Spatial Adjustment toolbar. Otherwise you would be using the two point transformation of the georeferencing toolbar that ultimately creates a world file. The Spatial Adjustment toolbar actually changes the coordinates of the data and accepts more than two points to "rubbersheet" data.
4. Setting the spatial reference for imported data can be accomplished on tools like the FEATURE CLASS TO FEATURE CLASS tool explicitely, but in most cases geoprocessing tools will automatically "set" the output spatial reference to be the spatial reference of the target data set. If the target is new and the tool does not include a parameter for the spatial reference usually the input will be used as the output spatial reference.
5. Data is automatically projected when a coordinate system is defined in the .PRJ file or as part of the MSD definition of an AuotCAD file. This would include things like Merging data, appending or viewing data in ArcGIS. CAD data that does not have a coordinate system defined with the appropriate WKT string in a .PRJ file or internal PRJ of an MSD formatted AutoCAD file will not be projected.
Post a Comment
<< Home