Applicability (Entity/Page Type - dialog tab):

Log - report structure

Description:

If set, the report determines the log starting depth as the difference between the surface elevation and this value. This is a value or (more likely) an expression that evaluates to an elevation value. This allows you to move the 0 depth line below the normal top of the log body.

Using the Reference Elevation Property

Let's say you have a project with boreholes along the center line of a bridge alignment that crosses a river. The borehole surface elevations at the abutments are at a maximum value of 200 feet and those in the river bed are about 170 feet. You could specify the reference elevation as 200 feet for all the boreholes. This would give the same relative scale to all the logs and allow a direct comparison that shows the relative vertical positions of the strata. In the case of the holes in the river bed, where logging starts, i.e., zero depth, would be about 30 feet down on the page.

Generally, when the reference elevation is used a field is set up in the PROJECT table to set a value and a comparable field is set up in the POINT table to override the value in the PROJECT table. This is for holes that may be so different in elevation (much higher or much lower than the typical range in the project) that you do not want to follow the same reference elevation used by all the other holes. This is to avoid having blank pages before the 0 depth is encountered or chopping off the top of the hole. Let's say we called this field "Reference Elevation" in both the PROJECT and POINT tables. The Reference Elevation expression in the Log Report properties would read:

<<FirstData(_
  <<POINT.Reference Elevation>>,_
  <<PROJECT.Reference Elevation>>_
)>>

i.e., use the value in the POINT table if it exists, otherwise use the value in the PROJECT table.

Notes:

When setting up log reports where you have multiple logs on a page vertically or horizontally this property is not used and must be blank.

Note that in logs, the Reference Elevation property will push down the 0 depth line if the Reference Elevation is above the surface elevation or start the log at a depth deeper than 0 if the Reference Elevation is below the surface elevation. There are cases where you may wish to push down to the 0 depth line not based on a Reference Elevation but just a depth. You could implement that by adding a field in the POINT table to specify the offset, let's call it Depth Offset. Then the Reference Elevation field would be:

<<Calc(<<POINT.Elevation>> + <<POINT.Depth Offset>>)>>

This will work. However, if you don't have an elevation for the Point then this technique will fail.

The correct way is to use the Top Depth Expression property. You would make the Depth Offset negative in this case.

Note that a print button appears at the bottom of the "zoomed" field dialog, that is, the dialog that appears on clicking the button with the ^ right of memo fields in dialogs. This allows you to print complex expressions for review on paper.