Dimensions not adding up

[Anonymous]

I run into this from time to time. I've also run into it in other CADD/BIM software. Anyone know what can cause this?

[vistasp]

Wrathchild, check your dimension accuracy settings.

In your dimension preferences, change the value of "fraction" to, say, 1/64 and see if you get a more accurate total.

What probably happening is that, for each sub-dimension, some amount of rounding off is taking place. The total is taken on actuals and then rounded off once only. That often leads to a discrepancy.

[David Maudlin]

Wrathchild wrote:
I run into this from time to time. I've also run into it in other CADD/BIM software. Anyone know what can cause this?

On the old ArchiCAD Talk forum (on AOL), Ferenc Lazar (Ferenc on this forum), explained that this was due to numbers being translated to and from binary code, so these sorts of things is inevitable. I can't recall the full explanation, perhaps one of the programmers here can give more insight.

David

[Anonymous]

vistasp wrote:
Wrathchild, check your dimension accuracy settings.

In your dimension preferences, change the value of "fraction" to, say, 1/64 and see if you get a more accurate total.

What probably happening is that, for each sub-dimension, some amount of rounding off is taking place. The total is taken on actuals and then rounded off once only. That often leads to a discrepancy.

I have that happen often.. someone changes the accuracy setting to be 1/2" or so and it messes up the overall dimension.

[Anonymous]

Is there a best way to set up a drawing to avoid this from the get-go? My builders don't want to see dimensions in 64ths.

[Anonymous]

Go to "options" "project preferences" "working units and dimensions." Save a setting for your office. I use 1/16" as my tolerance but never dimension to that. I only dimension to the 1/4" or maybe 1/8" at the least but by having the 1/16" it eliminates most of the dimensional rounding.

[Anonymous]

Steven wrote:
Go to "options" "project preferences" "working units and dimensions." Save a setting for your office. I use 1/16" as my tolerance but never dimension to that. I only dimension to the 1/4" or maybe 1/8" at the least but by having the 1/16" it eliminates most of the dimensional rounding.

I had it set to 1/8" but I'll give 1/16" a try. Thanks.

[Anonymous]

If you find dimensions are not adding up again (lets say for walls) just offset the wall the dimension you want it to be. The wall could say it's 12'-0" from another wall but it could actually be 12'-0 1/32", and that can mess up dimension strings.

[Laszlo Nagy]

David wrote:

Wrathchild wrote:
I run into this from time to time. I've also run into it in other CADD/BIM software. Anyone know what can cause this?

On the old ArchiCAD Talk forum (on AOL), Ferenc Lazar (Ferenc on this forum), explained that this was due to numbers being translated to and from binary code, so these sorts of things is inevitable. I can't recall the full explanation, perhaps one of the programmers here can give more insight.

David

I think nowadays this is simply a problem of rounding.
Here is an example:
You have 10.00 meters, which is divided into 3 dimension units. The distances are 3.333, 3.333 and 3.334, which add up to 10.00. Your accuracy is set to 2 decimals, so you will see 3.33, 3.33 and 3.33 displayed, respectively, which will not add up to 10.00.
If ArchiCAD was really smart, it would detect such a problem and round one of the dimensions accordingly. There would be an algorithm of which dimension unit changes the least with the modification or something like that.

However, it is possible that several years ago it was a matter of accuracy but as far as I know ArchiCAD has become much more accurate with AC 8 or one of those versions.

In any case, I would check my model to see whether those distances are really exactly match the lengths displayed by the dimensions, because in that case no rounding is necessary. If that does not help, then it may be a new accuracy problem in which case I am sure GS would be interested in the file.

[Anonymous]

laszlonagy wrote:

David wrote:

Wrathchild wrote:
I run into this from time to time. I've also run into it in other CADD/BIM software. Anyone know what can cause this?

On the old ArchiCAD Talk forum (on AOL), Ferenc Lazar (Ferenc on this forum), explained that this was due to numbers being translated to and from binary code, so these sorts of things is inevitable. I can't recall the full explanation, perhaps one of the programmers here can give more insight.

David

I think nowadays this is simply a problem of rounding.
Here is an example:
You have 10.00 meters, which is divided into 3 dimension units. The distances are 3.333, 3.333 and 3.334, which add up to 10.00. Your accuracy is set to 2 decimals, so you will see 3.33, 3.33 and 3.33 displayed, respectively, which will not add up to 10.00.
If ArchiCAD was really smart, it would detect such a problem and round one of the dimensions accordingly. There would be an algorithm of which dimension unit changes the least with the modification or something like that.

However, it is possible that several years ago it was a matter of accuracy but as far as I know ArchiCAD has become much more accurate with AC 8 or one of those versions.

In any case, I would check my model to see whether those distances are really exactly match the lengths displayed by the dimensions, because in that case no rounding is necessary. If that does not help, then it may be a new accuracy problem in which case I am sure GS would be interested in the file.

I don't really think my model could be the problem. I almost always (if not always) type in exact units when laying out my plans.