I have been delivered a .dgn file and I need to define a coordinate system for its model. The file's metadata states that it is in a State Plane coordinate system in U.S. Survey Foot, but when I select that coordinate system from the library, I get the dialog below, indicating that the Storage Unit is actually International Foot. Because the coordinate system in International Foot isn't available in the library, it seems to me I have two options:
1) Use the coordinate system from the library that's in U.S. Survey Foot and choose one of the options from the dialog that MicroStation presents:
2) Define a custom coordinate system with the same unit as the model and assign that coordinate system to the model.
Which is the best option to choose? If 1), which of those options do I choose? The second one will alter the contents of the original file, which is scary....
Several of my colleagues and I have read the article on the subject, and it's not making sense.
When dealing with different geographic coordinate systems and English units you really want to be using U.S. Survey Feet as the storage units. Things will work much better if you select the second option and have MicroStation change the working/storage units of the model.
Rod WingSenior Systems Analyst
Before choosing a route, you will need to determine which you believe is accurate:
(if not determinable, proceed with parallel testing of multiple outcomes)
The (external) metadata
or
The existing MicroStation working unit definition.
i.e. It is entirely possible that the operator created the file working in (International) Feet, whilst thinking they were working in US Survey feet. If the file was originally V7 file format, this could thus also be a matter of how the file was upgraded (settings, at the time of upgrade).
If you feel that that was the case (the values were input as US SF, while working in Ifoot, then you can correct the working unit definition and labels of the file before assigning the CS.
a) Settings>Design File>Working Units>(advanced settings)>edit...
Modify the resolution from
nnnnn per Foot
to
nnnnn per US Survey Foot
(OK)
b) Back in the Design File Settings dialog, modify the Master Unit (drop down) to label as US Survey Feet.
c) ...then, assign the USFT based CS definition.
Tips:
-Working unit changes, tpmode changes, etc. may require save settings to be applied to the dgn.
- keep a backup of the original, work in a copy.
- (Settings>Design File>Working Units>Accuracy) set coordinate readout to allow a high level of significant figures, to ensure accurate comparison.
Do this first, before making any comparisons.
- you can check coordinate points using tentative snap, but be aware of the tentative point mode that you are working in.
to query the current mode: SET TPMODE (then watch the message area)
Useful commands:
SET TPMODE LOCATE
SET TPMODE ASCLOCATE
- use the XYZTXT 'Label Coordinates' tool to label coordinates before (in 'ft') and after (in 'sf').
The coordinate values shown before and after the WU change, should match.