When zooming a mapper window to a small multiple of the internal precision, say 10 times, one can observe some interesting and some strange behaviors.
If a layer is editable, adding symbols will reveal the basic grid (add two symbols in the same place, then drag one progressively further horizontally or vertically from the origin until it does not snap back on the first when released, then use that distance as a guide for adding more).
Some results of editing operations may not be seen: a window redraw is practically required after each operation (addition or move) to see the results on the screen.
The Ruler command gives weird readings, bouncing by increments that have nothing to do with the precision level nor with pixel definition; it seems that it could be due to the truncation mentioned above.
On a UTM table bounded to 2 million meters in both directions, with a zoom of 1 meter on a default size mapper, the Ruler command gave the following readings (in cms) 9.49 13.43 16.44 18.99 21.23 23.25 25.12 .... with asymptotically decreasing jumps.
The Ruler command traces on the screen a measured path that is offset from the cursor position and the nodes of this path are not constrained by the basic grid. However, this may be due to the graphic card more than to MI as many PC's with differing video cards produce different results
The snap action is useless in the sense that the snapping distance within the window becomes inferior to the basic grid size; there is a zoom at which the basic grid overtakes the "set" snapping distance.
Estimate of snapping distance expressed in real world measurement:
p is pixel size (ex.: .28 mm), S the scale factor for the mapper (ex.:
1/10),n number of pixels for snapping as set in preferencessnapping distance = n * p / S (all expressed in the same unit)It is necessary to change the "distance units" used to post some mapping information (zoom or Ruler command) to be able to read with the same accuracy than the one available in the window; truncation has also its impact here. But the change has not effect on cursor location nor on object info window, the number of decimals there being determined by the existence of bounds. Editing techniques are also limited to direct positioning and shaping of objects because the ObjectInfo tool does not necessarily accept coordinates with the adequate number of digits.