User Guide
User Guide
User Guide

Evaluate Surface

Use it!

(3D only) Used to graphically and numerically evaluate attributes of a B-spline surface, other than order, poles, and knots, at given locations on the surface. There are four ways to define locations on a surface, and two output options.

The attributes that can be computed are points, tangents, and normal directions. Computed attributes can be used as reference points or reference lines for other purposes.

Tool SettingEffect
Attribute(s) Output By

Sets the method used to output the computed attributes:

  • Display Only
  • Save In File
    • — The attributes are saved in the active design file with the same graphic group number for easy manipulation.
Location(s) Input By

Sets the manner in which the locations on the surface are defined:

  • Enter Data Point
    • — interactively define a single location on the surface.
  • Parameter
    • — using the Parameter Value U and V settings. The values, which must be in the range 0–1, specify the location from the domain to map to the displayed object. Within MicroStation, the domain is from 0.0 to 1.0.
  • Dist[ance] Along Curve
    • — using the Dist From Start(%) U and V settings. The values are each a percentage of the total length of the u or v curve on the surface. For example, to extract the tangent direction of a surface at its middle point, set Dist. From Start(%) U and V each to 50.
  • Point Array option
    • — using the Number of Points U and V settings. The values are the number of evenly spaced locations on the u and v curves, respectively. For example, to evaluate at 200 evenly spaced locations on the surface, set Number of Points U to 10 and Number of Points V to 20.
Tangent Plot Scale

Sets the scale factor applied to the magnitude display. If set to 1.0, the computed tangents will be the true derivative vector — that is, the tangent direction with the magnitude.

Normal Plot Scale

Sets the scale factor applied to the perpendicular line segments in Normal output. If set to 1.0, the true normal vector is displayed — that is, the direction plus its true magnitude.

Parameter Value U/V

Sets the parameter values applicable to the Parameter option for defining locations on the surface; see Location(s) Input By above.

Dist[ance] From Start(%) U/V

Sets the distance values applicable to the Dist. Along Curve option for defining locations on the surface; see Location(s) Input By above.

Number of Points U/V

Sets the numeric values applicable to the Point Array option for defining locations on the surface; see Location(s) Input By above.

[Compute] Points

If on, the points on the surface at which evaluation is performed are displayed in the output.

[Compute] Tangents

If on, the surface's tangents are computed. In the context of this tool's operation, a tangent is computed as the partial derivatives of the surface in both parametric u and v directions.

[Compute] Normal

If on, the surface's normal directions are computed.

To evaluate a B-spline surface
  1. Select the Evaluate Surface tool.

  2. Identify the surface.
    If Location(s) Input By is set to Enter Data Point, this data point also determines the location on the surface at which to evaluate.

  3. Accept the surface.
    The surface is evaluated, and the desired attributes are computed and output.

Key-in: EVALUATE SURFACE

This tool can also be used to evaluate 3D primitive surfaces.