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Manually editing an object's position

Note: this borrows material from this topic on UKTrainSim.com. Thanks to those brave experts!

Some rolling stock such as cars and engines have child components such as lights, sounds, drivers and cameras whose position can be modified. This is also the case for some scenery items such as vehicles on a traffic ribbon.

3D games such as Railworks store information about the position, scaling and spatial orientation of objects in 3D position matrices.

For cameras, an easy way for doing this is by using Claudio's "RW Camera Cab Position" tool. It is payware, but there is no lower limit for the donation. It has a GUI that lets you position head-out or passenger view cameras and it will update the camera's position matrix for you.

For other child objects, or for those who prefer hacking the files, it is possible to edit the matrix directly in the xml blueprint or in GeoPcDx shape files. A matrix looks like this in an xml blueprint:

<e d:type="sFloat32" d:alt_encoding="000000A090F2EF3F" d:precision="string">0.99</e>
<e d:type="sFloat32" d:alt_encoding="00000020E945ADBF" d:precision="string">-0.05</e>
<e d:type="sFloat32" d:alt_encoding="000000A0F02E673F" d:precision="string">0.02</e>
<e d:type="sFloat32" d:alt_encoding="0000000000000000" d:precision="string">0</e>
<e d:type="sFloat32" d:alt_encoding="000000A0F5B7AC3F" d:precision="string">0.05</e>
<e d:type="sFloat32" d:alt_encoding="000000E009A1EF3F" d:precision="string">1</e>
<e d:type="sFloat32" d:alt_encoding="00000000020FC23F" d:precision="string">0.14</e>
<e d:type="sFloat32" d:alt_encoding="0000000000000000" d:precision="string">0</e>
<e d:type="sFloat32" d:alt_encoding="00000040A27B86BF" d:precision="string">-0.01</e>
<e d:type="sFloat32" d:alt_encoding="000000008E04C2BF" d:precision="string">-0.14</e>
<e d:type="sFloat32" d:alt_encoding="000000C0EEADEF3F" d:precision="string">1</e>
<e d:type="sFloat32" d:alt_encoding="0000000000000000" d:precision="string">0</e>
<e d:type="sFloat32" d:alt_encoding="00000020034085BF" d:precision="string">-0.37</e>
<e d:type="sFloat32" d:alt_encoding="000000C0CCCC0840" d:precision="string">3.1</e>
<e d:type="sFloat32" d:alt_encoding="000000E021371F40" d:precision="string">7.8</e>
<e d:type="sFloat32" d:alt_encoding="000000000000F03F" d:precision="string">1</e>       


To get the matrix from a GeoPcDx file, open it with RWTools and find the 'SourceLToPTransform' data block and the first series of sixteen data elements which typically look like this:
<e d:numElements="16" d:elementType="sFloat32" d:precision="string">0.9900 -0.0500 0.0200 0.0000 0.0500 1.0000 0.1400 0.0000 -0.0100 -0.1400 1.0000 0.0000 -0.3700 3.1000 7.8000 1.0000</e>

In both above examples, the values are shown in red. There are 16 of them. You must think of these 16 values as a 4 x 4 matrix, arranged as follows.

1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16

This is the position of each value in the 4x4 matrix. So the value on first line in the above xml node (0.99) is at the top-left corner in the matrix:

0.99 0.05 -0.01 -0.37
-0.05 1 -0.14 3.1
0.02 0.14 1 7.8
0 0 0 1

3D programs interpret the matrix as follows:



The top left corner (positions 1, 5, 9, 2, 6, 10, 3, 7 and 11) is a 3x3 rotation matrix


Top to bottom, rotation around X, around Y, around Z. You need to multiply (matrix multiply, not math multiply) the existing matrix with that, not just replace it, or you will lose any scaling.

To rotate the object horizontally through 180 deg. set elements 1 and 11 to -1.0000.

To rotate the object horizontally clockwise through 90 deg. set elements 1 and 11 to 0.0000, set element 3 to -1.0000 and element 9 to 1.0000.

To rotate the object horizontally anticlockwise through 90 deg. set elements 1 and 11 to 0.0000, set element 3 to 1.0000 and element 9 to -1.0000.

If you want to rotate in two or three dimensions you need to make a matrix for each rotation, and then multiply them together. It seems rotations are always around the local origin of the object which simplifies things enormously ( you don't need to worry about rotating and then translating vs translating and rotating, it's not the same thing! ).

There is an on-line rotation matrix calculator that will calculate matrix values for your desired changes. Remember, you need to multiply the existing matrix with that, not just replace it.


The last column, 13-14-15 is for translation ( ie positioning )

To offset object sideways, adjust element 13 (increasing value moves object left)

To change object height, adjust element no. 14 (increasing value raises object)

To offset object forwards or backwards adjust element 15 (increasing value moves object backwards)


Scaling is along the top-left to bottom-right diagonal.


Fairly obvious, position 1 is scaling by X, 6 is scaling by Y, 11 is scaling by Z, and 16 really should scale all of them - but trying this has produced some rather odd results.


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