Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

I have read a number of posts and tutorials, even the QGIS manual on snapping. I set the snapping options under settings>snapping options; selecting the two layers that I would like snapping on, setting the mode to vertex, the tolerance of 0.00002 map units and checked avoid int. and enable topological editing.

I moved the on polygon on layer one, grabbing the approximate vertex to the adjoining approximate vertex on layer two. at a scale of 1:500 it looks as though it snaps correctly, but when I zoom in to a scale of say 1:1 they are not aligned properly. Am I missing something or attempting to be to accurate?

Thanks for the input.

share|improve this question
    
What are you map units? 0.00002 seems really small –  Nathan W Jan 11 '13 at 13:24

1 Answer 1

up vote 5 down vote accepted

The tolerance of 0.00002 map units is obviously wrong. I have set my snapping tolerance to 10 pixels, which means that a point is snapped to an existing point if it comes nearer than 10 pixels.

With the small tolerance you set you avoid snapping in most cases, unless you are working in a scale of 50.000:1 (not 1:50000!).

share|improve this answer
    
Ok, so I changed it to 10 pixels and moved the polygon again. at a scale of 1:500 it looks good, but when zoomed into say 100000:1 its off. I know a map will never be viewed at that scale, but I guess its a question of accuracy. I came form the CAD world, where accuracy is vital. –  LandArch Jan 11 '13 at 14:10
1  
100000:1 is pretty dam small. I very much doubt you would need that level of precision in a GIS system. QGIS might not render accurately at that level too. –  Nathan W Jan 11 '13 at 14:58
    
Thank you for the input. –  LandArch Jan 11 '13 at 15:01
    
Best way to test the snapping is to move the node. With topological editing on, both polygon nodes should move together (You can Undo the move afterwards). –  Andre Joost Jan 11 '13 at 15:09

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.