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Volumetrics and zoom level

As with other users I am having difficulty creating repeatable volume measurements. In an answer to another user it was suggested that defining more perimeter points would help.

My problem is the fact that the conical dump that I am attempting to measure is 8 metres across, but the zoom in the map window gives out when the object on screen is less than 2 cm across. As a result laying down points around the perimeter is very imprecise.

This is problematic with a dump in that at this resolution, even if the dump is on a flat surface, it is quite easy to position a perimeter point on top of rocks on the dump itself rather than the flat surface, thereby causing an incorrect base calculation.

Why does zooming stop where it does. Is it because the image is at 100% - ie one image pixel per screen pixel? 

Ian Grierson

Official comment


If the base surface is flat, it doesn't really matter if you draw the polygon outside it a bit imprecisely. With the base defined along the flat surface no volume will be added to the total for that area so it is OK to draw outside the lines a little bit on that.

We usually draw the stockpile perimeters with the elevation map showing so we can clearly see where the stockpile begins and the bare base ends.

We already allow the map to be overzoomed one step beyond native resolution. It looks like a lot of your jobs have a reduced resolution for the source images which is making the GSD really high. Not only will the affect your ability to zoom in but it will affect the accuracy of the pile's volume calculations as well.

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Thanks for the prompt response. With regards drawing the polygon outside the pile I tried that but found that the further out I went (even though the surface is flat), the larger the volume. After your comment I tried the same experiment again and volumes remained much more consistent.

When you mention the elevation map, what do you mean? I didn't realise there was such a thing.

Point taken regarding the reduced resolution images. Two reasons for doing that:

1. slow internet connection at the minesite for uploading

2. keeping the maps free until we have completed our evaluation to see how useful the service is for us.

Feeling pretty positive about the latter at the moment except for these discrepancies in volumes from our own calculations and the problem discussed elsewhere regarding changing color balance from image to image (you have advised how to resolve this which is something I will try after Easter).

And I certainly can't fault your customer support. Your prompt and informed responses to questions are as good as any I have experienced.

Well done.



Ian Grierson 0 votes
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