Using NULL values in expressions

[cbaildon001]

Hi there

When I import survey data, sometimes my manholes have depth information and sometimes they don't.

I have a label style for manholes that show the lid level, the depth to invert and the invert level. This works well for manholes with depth information.

I have tried to create an expression that changes the text height of the depth and invert level to zero if the depth is zero or null.

IF(Point.Depth=0,0,0.0025) works for depths of zero but not null

IF(Point.Depth>0.001,0.0025,0) works for depths of zero but not null

IF(Point.Depth>0,0.0025,0) works for depths of zero but not null

How can I get an expression to work on a null value?

Cheers

[odoshi]

I don't have a dataset to test with, but did you try using ! ?

IF(!Point.Depth,0.0025)

I didn't see any built-in functions for Null and I am not sure what (if any) scripting language they are using.

Just a stab at it...

Mike

[jmayo-EE]

IF(Point.Depth=' ',0,0.0025)

IF(Point.Depth=" ",0,0.0025)

IF(Point.Depth= ,0,0.0025)

A few more to try.

[tcorey]

John, are you saying those worked or didn't work?

[jmayo-EE]

I did not test anything. Just came up with a few ways for the OP to test that might check for the null value...

[cbaildon001]

IF(!Point.Depth,0.0025) - this produces an error when saving the expression "wrong number of arguments"

[cbaildon001]

IF(Point.Depth=' ',0,0.0025) when saving the expression this produces an error 'parse error, undefined symbol ''

IF(Point.Depth=" ",0,0.0025) when saving the expression this produces an error 'parse error, undefined symbol "'

IF(Point.Depth= ,0,0.0025 )when saving the expression this produces an error 'parse error, unexpected ,, expecting name, function, number, (, +, -, or !'

[HorizontalCurveGuy]

make depth and invert seperate components

If(depth = 0 ,-1, <text height>)

if (depth =0,1,<text height>)

and hide negative values in the composer

[odoshi]

Sorry, I left out a param.

IF(!Point.Depth,0,0.0025)

It will compile but I don't have any dataset to test it with.

Regards,

Mike

[cbaildon001]

IF(!Point.Depth,0,0.0025) - Like other options I've tried it only works when the depth is 0 not NULL.

This issue has been ecsallated to Autodesk Support so hopefully they can come up with something, maybe 2016?

Thanks for your input.

[cbaildon001]

Hi HorizonalCurveGuy

I'm not sure how these are supposed to work

If(depth = 0 ,-1, <text height>)

if (depth =0,1,<text height>)

as my depth does not equal 0, it is NULL or no value.

Cheers

[loretom]

Caleb,

Did you ever get a response or resolution from Autodesk Support?  I too need a function that will equal null.

Thanks,

Miguel

[cbaildon001]

Unfortunatly no solution as yet. But please post here if you find one.

Cheers

[Joe-Bouza]

When you say Null value is that the structure type?

[cbaildon001]

NULL is for a measurement of the depth to the invert. So for example when I survey the location of a manhole lid, but I do not record the depth to invert as well.

[Joe-Bouza]

If the invert is Null isn't it 0 at the same time ?
You can nest your expression by looking and another parameter, for example have a structure specific to no depth info, then you can check for structure type

[loretom]

I think I might have posted in the wrong location.

What I am looking for is a way for the expression to return nothing.  Like in lisp you can set a variable to nil.  I am not looking for null.  I should have paid more attention.

All I wanted to do is setup an expression for labeling an alignment that would know when it is the end of the alignment and not place a station there.  I can get it to identify the end of the alignment, but all I can do is set it to 0.  This displays 0+00.  I know I can just delete that last station after it's put in, but I want the label style to do it automaticly.

Thanks,

Miguel

[cbaildon001]

Hi loretom

When I say null, I mean nothing at all, and empty data cell. So our queries may well be related. Civil3D does not appear to be able to recognise empty data fields in expressions.

Joe - Just to clarify, I'm not using 'structures' in Civil3D, just cogo points. I guess a invert of 0 could be interpreted as null or no value. But I don't want to have to enter 0 for every manhole I survey if I am not concerned with invert levels, I just want to be able to leave the field blank and be able

get an expression to recognise this.

Cheers

[Joe-Bouza]

No structures! that's a different ball of wax. The whole time I was thinking manholes and catch basins expressions. Oh well cancel all that. :0

[C3D_TomR]

Another instance of needing to check for NULL (not 0) values in an expression is if a surface spot elevation is outside of the surface the elevation value is NULL (not 0). If an expression could test for NULL values then the text height could be set to something not visible when it's outside of the surface extents instead of showing ??? as the elevation value.

Tom Richardson
CAD Manager
Crossing the line with Civil 3D
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