=====Making projected elevations=====

Whether you use an application like PocketTopo or SexyTopo to input your data, or whether you input the data manually, you may still end up wanting some kind of elevation from an angle that you were not originally able to draw sketches for. Most of these applications produce plan and extended elevations, and most manual surveys will do something similar.

You may find that you want a projected elevation for your survey. Sometimes you might not even know this until after you have compiled the data and rendered the centreline. Extended elevations are often easier to read for navigation, as passages never point towards the viewer, but projected elevations can show you the relationships between passages at different altitudes, or the surface, so there may be cases where they are preferred.

To draw useful sketches in XTherion, you will want to see the positions of the stations and centrelines. No matter how your data started its life, Therion can produce elevation views of the centreline data. It can either do this for the individual survey parts before they have been linked together, or it can do it after they have been linked together, or it can do it for the entire survey of all the parts. For most purposes, you will want to do this one sub-survey at a time, in the same way as you might do for a plan survey.

(Depending on what app you use to input your data, you may be able to ask it to export projected elevations of your centreline and splay legs. With PocketTopo surveys, this is done with the TopParser utility. However, this is not needed, since you can always do it with Therion itself.)

The advantage of doing this using Therion after linking all of your data together and adding declination information, is that error distribution and declination may change the orientation of some passages. Sketches made from unlinked data or without declination information may not appear quite correct if data correction or declination causes a passage to be oriented towards the viewer, when it previously pointed slightly away at an angle. You may have to make different choices with how you draw the scraps and maps, as a result. Declination does not have any effect on plans which can be simply rotated, or on extended elevations (error distribution has a minor effect), so this is not normally a consideration for those orientations.

To export an XVI image for a survey in Therion, use something like this in your thconfig:

<code>
source "overall.th"
select mysurvey@mycave.myarea
export map -projection [elevation 270] -fmt xvi -o "mysurveyElevation270.xvi"
</code>

Export it by compiling that thconfig. In the map editor view in XTherion, use "File - New", and save this file as mysurveyElevation270.th2 (or whatever naming works for you). Use "Edit - Insert image" and select the xvi file.

You will now need to create your scraps in the same way as for plan surveys, but this time select "elevation 270" or "elevation 270 degrees" as the orientation. Note that however you refer to it here, you will have to keep it very consistent - always use the same format. A bearing of 090 and a bearing of 90 are apparently different to Therion.

====No sketches====

At this stage, you may realise that you don't have any sketches from this angle. All you have are centrelines and splays. There does not appear to be any useful way of manipulating any existing extended elevation sketches or other projection sketches into this view. Sadly, this appears to be a completely manual task (but if you have any further hints, please add them here!). Some may favour the approach of physically printing it out, drawing on it with a pencil, then scanning it back in, and using that as a sketch.

It helps to have your original sketch (normally extended elevation) open somewhere, such as on whatever app you used to input the data, and refer to that to try to work out how the passage should appear. In the end, you still need to manually make a new drawing to reflect the passage's appearance from this angle.

====Identifying splays for a station====

You may find that the centreline and splays get extremely confusing when viewed in this way, since you now have all of them layered all over each other, and it can be quite hard to see which ones belong to which survey stations. Because you were not able to draw the sketch from this angle while surveying, you don't have anything easy to guide you. Even if you can see which splays belong to a point, you may not be able to see which ones are meant to touch the ceiling or floor, and which are aiming at a wall from an angle.

For this purpose, I like to use Survex's Aven. Ask Therion to export a 3D file:

<code>
source "overall.th"
select mysurvey@mycave.myarea
export model -fmt survex -o mycave.3d
</code>

Open this 3d file in Aven. Rotate it to the same bearing as your elevation. Select the station you are interested in by clicking on it. Zoom in enough to see the splays comfortably. Now quickly switch between plan and elevation view, eg. using the "P" and "L" keyboard shortcuts. As the passage rotates, you get a much clearer view of which splays end up where, so you can more easily identify them in XTherion's map editor.

====Colouring the elevations====

This section has its own topic: [[colouringelevations|Colouring elevations]]