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 map, 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 the native and proprietary format of Microstation. Contrary to what happens with a DWG that changes format every three years, there are only two DGN formats: DGN V7 that existed for versions of 32 bits to Microstation J and DGN V8 that exists from Microstation V8 and will remain in effect 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 Honduran Cadastre, back by 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 every change that was made on the map.

So, during 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, the date, the user and a description of the change; this is pure Microstation functionality that has since its V8 2004 version. A plus was to force through a VBA that forced the creation of the version 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 activated history 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 2015 property), what is new (the 433,435,436 properties) and in green what was modified but not moved. 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 suffered by the sector says how well the methodology was appropriated and continued, above all I am thrilled to see users with whom it was a pleasure to see a match of the national team: Sandra, Wilson, Josué , Rossy, el Chamaco ... 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 checked in countries in the same context where it was decided to save separate files for each change or simply the history was not saved. The only challenge was to think about how to recover via VBA that historical associated with transactions and converted into versioned objects of the space base.

2. Comparison of two CAD files

Now suppose that historical control was not stored, and that what is wanted is to compare an old version of a cadastral plan against one modified many years later. Or two plans that were modified by different users, separately.

To do this, the friends from across the border have provided me with a very useful tool called dgnCompare that has left me surprised. Only the two files are called, and it executes 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, deleted, even those that had minimal modifications such as color or line thickness. Definitely, that comparison manually 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 can be saved, dgnCompare is really useful to do 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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