How to compare changes to a CAD file

A very frequent need is to be able to know the changes that have happened to a map or plan, in comparison as it was before being edited or as a function of time, in CAD files such as DXF, DGN and DWG. The DGN file is Microstation's proprietary and native format. Contrary to what happens with a DWG that changes its format every three years, of the DGN there are only two formats: the DGN V7 that existed for 32-bit versions up to Microstation J and DGN V8 that exists since Microstation V8 and will remain in force for many years .

In this case we will see how to do it using Microstation.

1. Know the historical changes of the CAD file

This functionality was adopted in the case of the Honduras Cadastre, back in 2004, when the option of going to the spatial database was not a close thing. For this, it was decided to use the historical version of Microstation, in order to save each change that was made on the map.

So, for 10 years the CAD files stored each transaction of the change orders, it was versioned as seen in the following image. The system stores the version number, date, user, and a description of the change; This is pure normal functionality of Microstation that has since its version V8 2004. A plus was to force through a VBA that forced the creation of the versioning when opening the maintenance and at the end of the transaction. File control was done using ProjectWise, to prevent two users from using it at the same time.

No matter how primitive the procedure, the file without the history activated allowed to see the changes with colors; The map on the left is the changed version, but when selecting the transaction you can see in colors what was eliminated (the property 2015), what was new (the properties 433,435,436) and in green what was modified but not displaced. Although the colors are configurable, the important thing is that the change is associated with a transaction in the history that can even be reversed.

See how many changes this map has. According to the historical archive, the 127 maintenance that the sector suffered indicates how well the methodology was appropriated and continued, above all I am excited to see users with whom it was a pleasure to go to see a game of the national team: Sandra, Wilson, Josué , Rossy, the Kid ... capable and I get a tear. 😉

Although it made us laugh when in 2013 we decided to migrate to Oracle Spatial, and we saw it as an archaic functionality; we could not adopt it, which I have verified in countries of the same context where it was decided to save separate files for each change or the history was simply not saved. The new challenge was only to think how to retrieve via VBA that history associated with transactions and converted into versioned objects of the spatial database.

2. Comparison of two CAD files

Now suppose that no historical control was stored, and that what you want is to compare an old version of a cadastral plan against a modified one many years later. Or two plans that were modified by different users, separately.

To do this, friends on the other side of the border have provided me with a very useful tool called dgnCompare, which has surprised me. Only the two files are called, and it runs a comparison between the two realities.

Not only can the file be compared against one more, but against several; generates reports and graphic display of the objects that were added, eliminated, including those that had minimal modifications such as color or line thickness. Definitely that manual comparison would take hours, if not days depending on the amount of changes. Depending on the engineering application you are working on and how much time you can save, dgnCompare is really useful for doing that job in just a few minutes.

If someone is interested in seeing a demonstration of how dgnCompare works and how to obtain it, leave your in the following form a technician will contact you.

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