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Minor fix

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This commit is contained in:
Dion Moult
2021-07-06 12:33:05 +10:00
parent f7e550b926
commit 597b5ffbd6
1 changed files with 17 additions and 16 deletions
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src/blenderbim/docs/blenderbim/georeferencing.rst
+17 -16
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@@ -12,7 +12,7 @@ wild for vertical construction.
1. Correctly georeferenced IFC4 with a map conversion transformation
2. Correctly georeferenced IFC4 without a map conversion transformation
3. Invalidly georeferenced IFC4
3. Non-georeferenced georeferenced IFC4
4. Non-georeferenced IFC2X3
The first scenario is desired for most disciplines, such as architects and all
@@ -23,8 +23,8 @@ offset coordinates to preserve the precision of the model. The first coordinate
greater than 1km will be detected and used as an offset coordinate. It is
possible to specify a custom offset coordinate.
Invalid georeferencing
----------------------
Non-georeferenced workarounds
-----------------------------
The unfortunate reality is that IFC2X3 does not support georeferencing, and most
vendors have poor and inconsistent support for georeferencing, even in IFC4.
@@ -32,21 +32,23 @@ Some users may be under the impression that their file is correctly
georeferenced, but this is rarely the case. This creates problems. You can see
whether your file is correctly georeferenced in the ``IFC Georeferencing``
scene panel. If you see "Not Georeferenced", your file is not correctly
georeferenced.
georeferenced. If your file is georeferenced, it is no guarantee that the
georeferencing data is actually correct, but how to determine this is out of
scope of this article.
As an invalid workaround for proper georeferencing, many other BIM vendors
As an invalid workaround for correct georeferencing, many other BIM vendors
simply offset their object coordinates from local engineering to map coordinates
without properly storing the required transformation. There are two common
invalid workarounds that are used.
without properly storing a projection system and optionally a map
transformation. There are two common invalid workarounds that are used.
The first invalid workaround is to shift the origin point (known as the Object
Placement) of objects in the model. We call this the ``OBJECT_PLACEMENT``
workaround. The second invalid workaround is to shift the coordinates of
geometry within the objects themselves, and typically leave the object origin
untouched (such as back at (0, 0, 0)). We call this the ``CARTESIAN_POINT``
workaround. Sometimes, BIM applications combine both of these invalid
workarounds. To see which workaround was used on an object, check the "Blender
Offset" property in the ``Transform`` object panel.
The first invalid workaround is to shift the origin point of objects in the
model. We call this the ``OBJECT_PLACEMENT`` workaround. The second invalid
workaround is to shift the coordinates of geometry within the objects
themselves, and typically leave the object origin untouched (such as back at (0,
0, 0)). We call this the ``CARTESIAN_POINT`` workaround. Sometimes, BIM
applications combine both of these invalid workarounds. To see which workaround
was used on an object, check the "Blender Offset" property in the ``Transform``
object panel.
Coordinates and precision limits
--------------------------------
@@ -57,7 +59,6 @@ calculations. A full description of the precision implications are described in
the `Blender working limits documentation
<https://docs.blender.org/manual/en/latest/advanced/limits.html>`__.
From a software perspective, lengths greater than 5,000 meters start to
accumulate precision errors that affect the nearest millimeter. Therefore, from
a software perspective, it is unwise to embark on a project with coordinates