pt. protection tolerance

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pt. protection tolerance

Postby artb » Fri Nov 17, 2006 10:36 am

I am running into a very frustrating situation when trying to re-coordinate a point to put it more accurately on a line or curve.

I am in a project where there are many lots on a series of curves and it is consuming a great deal of time because you cannot get the routines to work consistantly.

Your program will not always change the coordinate as it suggests that the new result is inside the tolerance limit and therefore won't change the point.

Then when you try and draw a curve between the appropriate points it will then use that same tolerance limit to determine if it is a valid curve. It determines that it doesn't meet the tolerance and will not draw the appropriate arc.

I have had to delete a number of points and then recoordinate them to make it work.

This routine is intermittant in that it will sometimes work as it should.

It has succeeded and failed both in a straight traverse routine as well as in a bearing-distance solution.

I am suspicious that a negative difference may not be treated the same as a positive difference.

Any others experiencing this problem?????????.
artb
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Postby Glen Cameron » Fri Nov 17, 2006 8:23 pm

What value are you using for your Point Protection Tolerance?

I know the default value is very fine at 0.00001 and should be set to something that is appropriate for the type of work you are doing.

If Point Protection is turned on and the amount of the move of a point will be less than the Point Protection Tolerance value then the point is not updated to the new position. It is basically saying there is no change large enough to be considered so no change is made.

If you wish to have the point move to this new position then turn the Point Protection Toggle off or change the Point Protection Tolerance to an appropriate value.

When doing a 3 point inverse to generate a curve, the amount of difference between what is the correct and perfect position and the actual position of the third point is compared to the Point Protection Tolerance and if it is grater then the curve is not generated. You will get a dialog showing the baseline/offset and Perpendicular tie calculations instead.

To have the curve generated in a case where the distance is not perfect between the third point and the correct and perfect location, you would need to ensure the Point Protection Tolerance is set large enough.

This technical note may help show what I have mentioned here. Pick Here

What it boils down to is that the Point Protection Tolerance is not a static number and may need to be changed by you to meet the needs of the calculation you are doing at that point in time. All comparison distances are positive numbers when compared to the Point Protection Tolerance and the quadrant or direction of travel does not make a difference.

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
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Postby artb » Wed Nov 22, 2006 12:42 pm

2006/11/22

If I understand your program controls properly I expect that the display controls (# of decimals to show for a distance) are just for the display. That is the distance shown on a plan will round off to 3 decimals (set at 3). I do not expect that setting to have any control over the other setting (Point Protection Tolerance) where it is comparing a measurement to confirm its accuracy to the decimal controls you set for point protection tolerance.

If my understanding is correct then your explanation doesn't explain why ,on some occasions, your recalulation routines for a point will NOT change even tho' the change is greater than the PPT setting calls for.

On the example I put out in my initial comments I had a number of points that I could not get your program to change even tho' my settings should have required a co-ord change.

Then after not making the change your program would then disallow an arc to be plotted because the radius comparisons did not meet your PPT limit that I had set. The only way that I could get it to work was to delete the point, reco-ord the 2 points from the center and then draw the arc.



I know that this situation is not universal so there is some scenario's where this problem may be triggered but I haven't determined what that scenario may be.
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Postby Glen Cameron » Wed Nov 22, 2006 1:48 pm

Your first paragraph is correct. Labeling is just that, Labeling, and does not affect the way calculations are done and what is displayed in those calculations. The technote just clarifies why you see the same distance on 2 lines but the PPT and 3pnt inverse do not see it that way.

I have not run into a case that does what you have descibed. If I set my PPT to a value - any point being moved further than the PPT value, if PP is ON, will trigger the PP dialog box. Unless the database and drawing are out of sync (confirmed and fixed with the MSAudit routines), I can't see why it would not work as it should.

As always, If you have an example that we can look at, please send it to me (DWG and MSD files), with an explanation of what you are finding and the values being used.

(I did find a small error in the Point Protection Tolerance technical note I had referred you to previously - it has been corrected and should be updated on this web-site shortly.)

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
Glen Cameron
 
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada

Postby rwhatman » Wed Nov 22, 2006 2:05 pm

I don't know if this will help.

vector/<Base>:
Displacement point:
arc (bc=10, ec=79, rad=120, is not being redrawn because the difference between the 2 radii is greater than pt. protection tolerance
10 N: 10387.761 E: 10262.709 El: 0.000 D:


I moved a point 0.002 on a curve. My point protection is set for 0.00001

The point did move, but the arc was not redrawn.

I did try a 1 metre move and the arc was redrawn.

I think I know the problem, its the SNAPS
Not all Snaps are equal. Make sure you use only have one snap at a time.

Then END SNAP will over ride a intersection snap.

This maybe why some of your points don't move.
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Postby Glen Cameron » Thu Nov 23, 2006 5:52 am

Entity Snaps will cause problems in many cases because they are normally applied to the drawing after the calculation is complete. So the Entity Snaps will often over-ride the position that you calculated.

I would recommend that when you are running COGO and other survey routines, that you do not have any Entity Snaps turned on. They are for CAD commands, not Survey commands.

This may be the source for the confusion - but then again, maybe not. :lol:

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
Glen Cameron
 
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
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