Design File Precision with a Latitude Longitude Projection

With thanks to Mike Horsfall for the following information. 

In MicroStation V8i, you can set the Geographic Coordinate System (GCS) of a design file to a latitude / longitude projection such as LL83.  To do that, simply go to Tools > Geographic > Select Geographic Coordinate System and choose the desired system from the supplied library.  For additional information, please refer to the following Wiki article: Geo-Coordination With MicroStation

When the GCS is changed to latitude / longitude, you'll be prompted to change the storage units from it's current setting to degrees as illustrated:

Once the storage units have been changed to degrees, take a peek at the working units of the design file and notice that the resolution is now based upon a degree rather than the original units.   

The following image shows the original units of resolution as being 2500/m.

Once a latitude / longitude GCS is assigned, the units change to 2500/degee as shown:

In some situations the resolution per degree may not be adequate which will inhibit you from being able to zoom in close enough to the design elements.  This may occur if you import or reference a SHP file with default settings.

In this case, the resolution needs to be increased by several orders of magnitude, say to 10,000,000. Let's take a closer look.

The earth is about 26,000 miles (137280000 feet) in circumference and that's 360 degrees.  This means that one degree would be would be 137,280,000 / 360 or 381,333.333 feet which is about 72 miles.   For those of us who are metric, this would be about 116km. 

When the design file is set to 1000 units of resolution per degree, it would result in each unit being 381 feet or about 116 meters.

Likewise, when the design file is set to 2500 units per degree, each unit is about 152 feet or 46 meters.

However, if the resolution is set to 10,000,000 units per degree, then a unit becomes 0.038 feet or 0.011meters which may eliminate zooming and drawing issues.

To make this change, select Settings > Design File  and choose Working Units.  In the Advanced Settings area, click Edit and acknowledge the alert by clicking OK.

In the Advanced Unit Settings dialog, change the resolution to the desired value and click OK.  You can then dismiss the Design File Settings dialog by clicking it's OK.

Note:  I'm not recommending a specific value for the units of resolution.  This article is simply showing an advanced setting and how it relates to map precision.  This setting needs to be determined by you based upon your own mapping needs. Also, this does not change the accuracy of the original data.  If the data was only accurate to 50 feet before the change in resolution, it will still only be accurate to 50 feet after the change.

Lastly, if you're dealing with importing data to a file set up in degrees, it's suggested that you adjust the resultion before doing the import. 

Related Information:

Projections

Using Longitude And Latitude Coordinates

Geo-Coordination With MicroStation