MicroStation InRoads General Standards
All MaineDOT MicroStation Files are 3D. While MicroStation provides for 2D and 3D .DGN file types, MaineDOT uses 3D files exclusively.
MaineDOT has changed units for InRoads files to U.S. Survey Foot
In 2006, MaineDOT made a decision to migrate from MX to InRoads. In order for InRoads and MicroStation to work well together, we made several changes to our MicroStation configuration and standard seed files. The following are the major points:
- Change in Units to US Survey Foot
Due to decisions made many years ago, the survey and mapping community in the United States uses a slightly different definition of the length of a "foot" than does the rest of the world.
1 US Survey Foot = 1.000002 International Foot
This is a difference of 2 ten-thousandths in 100 feet. It is generally not significant when measuring distances within our projects. However, the origin of our coordinate system is far enough away that you will have a significant error if you try to superimpose (reference) graphics drawn in one system over graphics draw in the other.
Our prior system was sort of a hybrid setup, where MX work was done in the US Survey Foot, but our MicroStation files were based on the International Foot.
Due to the fact that InRoads does its work within the MicroStation graphics environment, we had to bring them into alignment. Therefore, on new projects, both InRoads and MicroStation are now being set up on the US Survey foot definition. This is defined in our custom units.def file which is located in our !msInRoadsconf\standards\data folder.
- Change to Units of Resolution (UORs)
When we first developed our MaineDOT MicroStation configuration, there were several limitations in the software that have been removed in more current versions. In our earlier system, we chose a resolution of 1524 units per International Foot. This provided a convenient ratio for switching between metric and imperial units, and represented the best compromise between the size of the Design Plane and the accuracy desired for survey computations, etc.
Now, MicroStation no longer requires a trade-off between the size of the Design Plane and the level of accuracy. We now use a resolution of 1000 units per millimeter, which is the same as used by some other DOT's. While that resolution seems like more than we would ever need, it pretty much assures that MicroStation-induced rounding errors will no longer be a problem in survey and alignment calculations.
- Updating old files to new UORs and Units
The downside of the "improvements" in the Units and UORs is that we need to convert old files to the new setup, in order to use them together with new files.
This conversion is tedious to do manually, and subject to user error. Therefore, we wrote a program (VBA macro) to do this conversion. After conversion of the older files, references will line up correctly. In MicroStation's main menu, under the InRoads pull-down, look for "Update UOR and units".
- Expanded Level Structure and Naming
Bentley's "best practices" suggestion for InRoads configuration requires that names be coordinated for InRoads Features, Styles and Named Symbologies, as well as MicroStation Levels.
Implementing the above recommendation requires that there be one named level corresponding to each named feature (For MX users, a feature name is approximately the same thing as a string label).
MicroStation now supports a practically unlimited number of levels.
We looked at naming convention used by other D.O.T.'s, but decided to use similiar naming convenetion used by the US military (our old-time GDS users will recognize this) which goes from the general to the specific.
In the example here, the first "D" stands for "designed". An "S" stands for "surveyed", "M" stands for "mapping surveys", "P" stands for "proposed Right of Way", "E" stands for "existing Right of Way" etc.
This convention seems much more readable and user-friendly than the coded naming convention used in some of the DOT's.
Our new Level Naming convention and structure provides space for the earlier 63+ levels. Therefore, older MicroStation graphics may be combined with the newer graphics without conflict.
Management of the new level structure is accomplished using a .dgnlib file. This is an empty library file that contains the level structure consistent with MaineDOT standards. This is important for the management of the level structure. When a change to the level structure is necessary, the MicroStation files will automatically synchronize themselves to the library file.
- Border size for projects in U.S. Customary units
Our Full-size plan sets are now 22” x 34”. However, we are still printing on a 36” wide roll stock with a slightly oversized left margin. We are not trimming these plans in-house, so consultants are not required to do so.
Our Half-size plan sets are now 11” x 17”. We are still printing them on 18” wide roll stock, with an oversized left margin.
The border’s plot boundary shape measures 22” x 34” in full size and 11” x 17” in half size.
This change makes it possible to print Half-size plans to scale on standard 11" x 17" paper.
- Engineering Signatures & Seals
For U. S. Customary projects, we are including an Engineering signature and seal box on all sheets in a plan set. However, we still use a Engineer's signature and seal only on the title sheet, unless a different Engineer is responsible for specific sheets within the plan set.
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