Draw a Box in Feet and Inches
Original Article Engagement:Feb 23, 2005
Updated: October 4, 2011
With many thanks to Bentley's Dan Ahern from Bentley Civil Professional Services for contributing this article! Written for those of you who are having to deal with Survey Anxiety in MicroStation, this article contains essential information regarding the human relationship between V8's working units and setting your file upwards in survey feet.
Working Units
Working units have been, and keep to be, a pregnant part of MicroStation. In the past, the working unit of measurement divided up a fixed drawing space into a grid. Since the drawing infinite was stock-still, there was a trade off between decimal places and cartoon size. The larger the cartoon, the fewer decimal places were available. MicroStation V8.5 has a practically unlimited drawing space. Every coordinate in the cartoon space is calculated and stored to a full double precision number. In MicroStation V8.5 working units take a dissimilar purpose. They now define the cartoon unit so that MicroStation can properly compare two drawings and compensate for dissimilar units if they exist. For example, since MicroStation V8.5 understands units, it can correctly reference together a drawing in feet with a cartoon in meters without the user having to adjust the calibration, position or global origin. The working unit definition remains on the DGN File Settings dialog box.
Working units define the unit of measure in each model. Every model in a .dgn file has its own working units and each tin can be different. In most situations the only working unit of measurement definition that needs to exist done with MicroStation V8.5 is to identify the primary (master) and secondary (sub) units of measure. The Avant-garde and Custom settings are not typically needed. Since most everyone uses a small set of mutual units of measure, they have been built into MicroStation V8.five and are selectable from an option list.
To define the working units, select the desired unit for the primary (master) and secondary (sub) unit of measurement. If desired, the Characterization for each unit can exist modified. MicroStation understands the mathematical human relationship between the units and can adapt any choice of units. For instance, a valid, albeit strange, set up of working units could exist anxiety for the master unit of measurement and millimeters for the sub unit of measurement. There is almost never a need to utilise the Custom Units button. Later you will larn a better method to define units that are not included in the default MicroStation interface. The nearly common additional unit needed past Engineers is the Usa Survey Human foot.
Advanced Working Unit Settings
The Advanced push button opens the Advanced Unit Settings dialog box. These settings define two items. The first establishes the size of a filigree (like to the blueprint plane in MicroStation/J) that overlays the drawing expanse. This grid is used for backward compatibility with older versions of MicroStation. The resolution value does not affect the accuracy of a MicroStation V8.5 model. Changing its value will not increase or decrease the accuracy of the model. However, it tin can make it such that the model is not properly exported back to a MicroStation V7 file.
Note: The Resolution setting is disquisitional to the proper operation of GEOPAK. The Resolution unit (Foot in the illustration) must match the Master Unit and the Unit System defined in the GEOPAK Preferences. This is discussed in more detail later.
The 2nd setting is used by the solids modeling engines built within of MicroStation V8.5. The solids modeling engines require a finite working cube, but MicroStation V8.5 has an unlimited drawing plane. Therefore, a fixed design cube must be defined for the solids modeling engines to function properly.
Agreement MicroStation V8 Coordinates
Previously information technology was stated that MicroStation'due south new Working Unit definitions allow it to sympathize the human relationship between dissimilar units and automatically compensate for dissimilar drawing units when attaching cells and references. How does it work?
Understanding MicroStation Working Units requires understanding a niggling fleck about descriptive geometry and mathematical coordinate systems.
What is a coordinate system?
Although in that location are many different types of coordinate systems, they are all systems to locate the position of a bespeak relative to another known location. MicroStation uses both Cartesian and polar coordinate systems. Both systems locate a indicate position measured along two axes (2-dimensional coordinate system) or along iii axes (three-dimensional coordinate arrangement) from an origin location. The origin is the location where the reference axes intersect. The origin has the coordinate 0,0,0 past definition. The Cartesian coordinate arrangement locates the signal equally a linear measurement forth each axis. For example, a betoken at location (3, 5, ii) is three units in the X direction, five units in the Y direction, and ii units in the Z direction from the origin. The polar coordinate arrangement is based on the aforementioned coordinate axes, the difference is the point is located by measuring the distance and the angles betwixt the centrality and a line fatigued between the origin and the point.
The fundamental to agreement how MicroStation converts graphics from i coordinate arrangement to another is understanding that the origin or 0, 0, 0 coordinate is the common point between all coordinate systems. When MicroStation coverts from one coordinate system to another, it does and then by scaling the coordinates relative to the 0, 0, 0 origin point. For example, consider a trapezoid drawn in a file with English language units (feet). The coordinates of each vertex are shown in the following illustration.
If the file is converted to, or attached to a file with Metric units (meters), the trapezoid is resized by scaling the coordinates along a line between the original graphic vertex and the origin. In the following analogy, the trapezoid is scaled to be at the equivalent metric coordinates.
Foot vs. Survey Foot
Did you know there are two dissimilar lengths of a foot in the Usa? There are, and MicroStation V8 must be setup correctly or yous may not exist drawing what you think you are drawing. Internally MicroStation stores everything as a meter. Actually the meter is the official base unit of measure throughout the earth. Fifty-fifty though anxiety and inches are the dominant units of measure in the Us, they are legally defined relative to a meter.
MicroStation uses the working unit of measurement definition to catechumen coordinates and distances to and from meters. Therefore, when the working units are gear up to feet and inches, MicroStation nonetheless stores the coordinates in meters and converts to feet and inches to display coordinates, distances, measurements, dimensions, etc.
Considering MicroStation V8.five converts all values from feet (or whatsoever other unit) to meters to shop the information, it is critical that you sympathize the conversion process and the desired foot measurement. If not, your data may non be correct. Before we get into MicroStation farther, take a minute to review the deviation betwixt a foot and a US Survey foot.
The following definition is taken from the 1991 edition of ASTM publication E380-89a (Standard Practise for Utilize of International System of Units):
"The U. Southward. Metric Law of 1866 gave the human relationship, ane metre equals 39.37 inches. Since 1893 the U.S. chiliad has been derived from the metre. In 1959 a refinement was made in the definition of the 1000 to bring the U.S. yard and the yard used in other countries into understanding.
The U.South. yard was changed from 3600/3937 chiliad to 0.9144 m exactly. The new length is shorter by two parts in a million. At the same time information technology was decided that any data in feet derived from and published as a result of geodetic surveys within the U.S. would remain with the old standard (1 ft = 1200/3937 m) until further decision. This foot is named the U.S. survey foot."
Therefore the following definitions are in existence today:
1 human foot = .3048000 one thousand
one survey foot = 1200/3937 k » .3048006 grand
IMPORTANT: The human foot used past MicroStation in the standard unit list is based on the International Foot definition, not the United states Survey Foot definition. This is the right definition for nigh work outside of the civil engineering science and surveying disciplines. Many states go along to base their survey work on the United states of america Survey Pes. You must verify the basis of the survey for your projects to ensure you are working in the right units of measure out. If the information is based on The states Survey Pes survey measurements, using the standard pes definition (International Feet) in MicroStation will yield wrong results on the gild of 6 feet at a coordinate of 1,000,000
MicroStation does not include the survey foot in the standard unit list to avoid confusion for those who practice not understand the divergence between a pes and a survey foot. Nevertheless, MicroStation does sympathize the survey foot, the definition simply needs to be enabled. All MicroStation units are defined in a units.def file. The survey foot is already included in this file, it just needs to be activated. The units.def file is an ASCII text file located in the .../Workspace/System/Data folder inside the MicroStation installation dirctory.
The units.def file already contains the survey foot unit definition, withal it is commented out by default. Remove the pound (#) symbol from the kickoff of the line as shown in the above illustration to enable the unit definition.
Once enabled in the units.def file, the units are available for selection in the Master Unit and Sub Unit boxes.
NOTE: The inclusion of custom units in the Master Unit of measurement and Sub Unit drop downwards lists is new to MicroStation V8.5. In MicroStation V8.0 and V8.1, the custom units such every bit Survey Feet had to be defined by either importing a V7 file or using a keyin as described below.
The labels at the beginning of each unit definition line in the units.def file are used when a MicroStation V7 file is converted to a MicroStation V8 file. For instance, when a MicroStation V7 file working unit labels ft or ' is imported into MicroStation V8, it is automatically converted to International Anxiety because the label on the Human foot definition in the units.def file includes ft and '. When multiple definitions incorporate the aforementioned working unit of measurement labels, such as the Foot and Survey Foot practice in the default units.def file, the first definition is used. Therefore, when both the Foot and Survey Human foot definitions are active (# removed from beginning of line), the Foot definition will always be used. To force the Survey Foot definition to be used, either motility it higher up the Foot definition in the units.def file or delete the ft and ' labels from the Foot definition.
When using MicroStation V8.0 or V8.1, the survey human foot units are activated in MicroStation in ane of two methods. Both of these methods still work in MicroStation V8.5, but are non required since the survey foot unit can be selected directly from the dialog box.
Method 1: If a MicroStation V7 file is converted to MicroStation V8 and the Main Unit in the V7 file matches i of the label units for the survey foot in the units.def file, the working units in the MicroStation V8 file are automatically prepare to Survey Feet.
Method two: An existing MicroStation V8 file is updated to the Survey Foot working unit by issue the keyin: gear up units "Survey Feet"
The working units are set up to the survey foot definition instead of the default foot definition.
WARNING: The 'fix units' keyin method only sets the Chief Unit and Sub Unit of measurement values to Survey Feet. It does not set the Resolution Unit on the Avant-garde Unit Settings dialog box. The Resolution Unit remains with its previous definition resulting in the Master Unit and the Resolution Unit of measurement having different values as shown beneath.
For GEOPAK users this is a critical upshot. The issue is that GEOPAK looks at the Resolution Unit to make up one's mind the unit system and MicroStation looks at the Master Unit. Therefore, the result is that MicroStation is working in U.s. Survey Feet and GEOPAK is working in International Feet.
To avoid this trouble, GEOPAK users tin create a new MicroStation V8 seed file by
converting a MicroStation V7 file. When the V7 file is converted, and the units.def file is active with the survey foot definition, both the Main Unit of measurement and the Resolution Unit of measurement are set to Survey Feet. This seed file can then be used in MicroStation V8 to create all hereafter files.
In MicroStation V8.v, you can also select the Survey Foot unit on the Avant-garde Unit Settings dialog box. Prior to MicroStation V8.5, the Survey Foot unit could non be selected on the dialog box. The only selection was to create a new MicroStation V8 file by converting a MicroStation V7 file.
If y'all are working in InRoads or pure MicroStation, this will not be an result.
Boosted Reading
The divergence between Usa Survey Foot and International Human foot
A discussion regarding survey anxiety when converting to V7
What is a human foot?
AskInga Commodity #233
Source: https://communities.bentley.com/products/microstation/w/askinga/1035/working-units-and-survey-feet