Issue
The simplest way, ensuring accurate results
Solution
The following steps are taken from the tutorial that can be found in the on-line help. The illustrations are taken from the tutorial that guides you through the drawing process, so you have a building as shown in the view of the west facing wall in step 1 below. Note the coordinates in Step 4 (-199.9). This reflects the position of the building. If the face of your building is in a different location, the equivalent adjustment, to lift the calculation points slightly clear of the building face will similarly ensure the points are in front, and not obscured by your 3D face.
Step 1 - Set the view to the side of the building
In order to define the calculation grid on the west-facing wall, we must adjust the AutoCAD screen view to look East. Use the AutoCAD -VPOINT command, and use the viewpoint (-1,0,0).
Command: -VPOINT ?
*** Switching to the WCS ***
Current view direction: VIEWDIR=-1.000,0.000,0.000
Specify a view point or [Rotate] <display compass and tripod>: -1,0,0
*** Returning to the UCS ***
Regenerating model.
Command:
Then zoom and pan to obtain this approximate view:
There is one more thing to do: Set the coordinate system to coincide with the current view. Use the AutoCAD command UCS, then choose the "View" option to redefine the local coordinate system:
Command: UCS ?
Current ucs name: *NO NAME*
Specify origin of UCS or [Face/NAmed/OBject/Previous/View/World/X/Y/Z/ZAxis] <World>: v ?
Command:
Step 2 - Add new calculation grid type (vertical)
Issue the GridPts command again. Since we have previously defined a grid, this time you will see:
Highlight the choice << Add a NEW definition >> and click Next to bring up the Calculation Points screen.
Alter the description to read as shown, then click the topmost Next button ('HORIZONTAL FOOTCANDLES') as before.
Step 3 - Select ‘vertical’ illuminance
We want Vertical footcandles, not horizontal, on this grid, so we must override AutoLUX's default choice of horizontal FC. Set the buttons as shown. Also, we want to set the color to yellow so as to distinguish this grid's computed results from those from Step 6 (set in Step 7).
Click Change Color to bring up the standard AutoCAD color selection palette.
Choose yellow and click OK.
The screen should now look like this:
Now click Accept, then OK to return to the AutoCAD command prompt.
Step 4 - Orient the coordinate system to the vertical building wall
Since we redefined the local coordinate system (in Step 10), note the following correspondence between the current and global coordinate systems:
| Current | Global |
| + X | - Y |
| +Y | + Z |
| + Z | -X |
We must keep this correspondence in mind as we locate the points on the facade. Thus, if we locate our lower left target point (as we look East) 5' above and 5' right of the building corner, its global (x,y,z) coordinates will be (200,195,5). Per the above table, however, the local coordinates of the same point are (-195,5,-200). Issue the command. Since we now have 2 grid definitions, this time there will be two choices in the list box.
Highlight the "Vertical FC on west-facing wall" choice and click Next. In response to the prompt "Pick a corner point:", key in -195,5,-199.9 and press Enter. Why -199.9 and not -200? Since the facade is also an obstruction, we want the grid to lie a finite distance off the wall. Otherwise there is danger that computer roundoff would cause the wall to block light falling on the grid. When you are prompted for the Opposite Corner, drag the rubber-band line to the upper-right corner of the wall as we are looking at it, and click a point just inside the wall outline. The screen should now look like this:
Step 5 - Return to plan view and coordinate system
Now that our target grid specification is complete, let's return to plan view, via these two AutoCAD commands:
| a) | -VPOINT | Viewpoint 0,0,1 |
| b) | UCS | Enter option View (‘v’) |
Command: -VPOINT ?
*** Switching to the WCS ***
Current view direction: VIEWDIR=-1.000,0.000,0.000
Specify a view point or [Rotate] <display compass and tripod>: 0,0,1
*** Returning to the UCS ***
Regenerating model.
Command: UCS ?
Current ucs name: *NO NAME*
Specify origin of UCS or [Face/NAmed/OBject/Previous/View/World/X/Y/Z/ZAxis] <World>: v ?
Command: