RTD STRETCH: FAQs for Beginners
Frequently Asked Questions: A Beginners Guide
This guide is written for someone who has never designed a tent. It assumes no engineering background and no prior knowledge of fabric structures. It explains what the parts are called, what each control actually does to the shape, and how to tell whether the design you are looking at is a good one. Read it in order the first time. After that, use it to look things up.
Starting out
What is RTD Stretch?
It is a design tool for stretch tents. You describe the tent you want, in plain dimensions, and it builds a three dimensional model of the fabric and the structure holding it up. It then gives you the geometry numbers, the plan drawings and the 3D files you need to have the 3D model of the tent taken into other software to get the tent made and put up.
I have never designed a tent. Can I actually use this?
Yes. The software carries defaults that produce a sensible tent the moment it opens, so you are always adjusting a working design rather than building one from nothing. The best way to learn is to move one control at a time and watch what happens to the shape. Nothing you do is permanent, because everything can be undone.
What is a stretch tent?
A stretch tent is a tent with no rigid frame. A single sheet of stretchy fabric is pulled up over poles and pegged down at the edges, and the shape comes entirely from the tension in the fabric and the cables at its edges. This is why it looks the way it does, all curves and peaks, and why there should be no such thing as a flat panel in one. It is also why the design process is different from a framed marquee: you are not assembling parts, you are finding a shape. RTD Stretch produces a geometrically accurate 3D model but unlike analysis software, the choice of shapes, high and low points, and pole configurations is the choice of the user. It is possible to create non-optimal shapes with RTD. This is exactly why we provide NO WARRANTIES with RTD other than the production of accurate models for conceptual design, or as a sales tool using the Insert Background Picture feature for showing a simulation of the tent in its intended site or for taking into a generative AI video creation tool such as Google Veo.
I have worked with pole tents. Does any of that knowledge transfer?
Almost all of it. A pole tent and a stretch tent are far more alike than they are different, and they share very nearly every component in this software. Both stand on kingpoles in the middle and side poles around the perimeter. Both use bale rings at the pole tops to spread the load into the fabric. Both are held up by guy lines to the ground, and both live or die by where those guys can be pegged. Both carry the fabric edge on a catenary between the side poles. Both have ridges along the high lines and valleys at the low lines, and both pond in exactly the same places for exactly the same reasons. If you have put up pole tents, you already understand most of the vocabulary in the control panel, and most of your instincts about what will drain and what will not are sound.
What is actually different, then?
The fabric, and therefore how the shape is arrived at. A pole tent is made from panels cut and sewn to a pattern: the shape is largely decided on the cutting table, and the poles then push that pre-made shape up into position. A stretch tent is one stretchy sheet, so the shape is not cut in at all. It emerges from the tension when you pull it up, and it changes the moment you move a pole or a peg. That is the reason this RTD software recalculates the roof every time you touch a control, rather than just redrawing it. Everything around the fabric, which is to say the poles, the rings, the cables, the guys and the geometry, works on the same principles for both. Note that complex models may have a slight delay in redrawing the stretched roof on older or slower computers. The very amazing feature of RTD, the ability to alter pole positions in X coordinates, ie to the right, (or to the left in minus X coordinates), and also in the Y coordinates or change the height makes every part of the RTD tent model infinitely variable.
What are the main parts?
Kingpoles. The tall poles in the middle that make the high peaks.
Side poles. The shorter poles around the perimeter that hold the edges up.
Edge cables. The cables running along the perimeter between side poles, which the fabric edge follows.
Guy lines. The ropes running from the poles down to the ground, which stop them falling over.
Bale rings. The rings at the top of the kingpoles that spread the load into the fabric.
Ridge and valley cables. Cables running through the roof that control the high lines and the low lines.
Everything in the control panel adjusts one of these.
What is the normal order of work?
Work down the control panel. It is arranged in the order you would actually build a tent: choose the mode, set the plan dimensions, set the pole heights, configure the kingpoles, shape the roof and cables, choose the mesh, then read the statistics and export. Resist the urge to jump around at first, because later controls assume the earlier ones are settled.
What is the difference between the modes on the menubar?
Stretch Tent Version is the main design mode and the one most of this guide describes. Stretch Tent Builder and Round Tent Builder are two separate environments for laying out a tent that does not fit the standard rectangular arrangement. They are described in their own section below. Start in Stretch Tent Version.
Is there a manual inside the software?
Yes. The Help Guide opens from the menubar and contains the full user guide, organised into chapters, with no internet connection needed. This FAQ is the beginners route in, the Help Guide is the reference.
The parts explained
What is a kingpole and how many do I need?
A kingpole is a tall central pole that pushes the fabric up into a peak, and it does the same job in a pole tent as it does here. The number of kingpoles sets the number of peaks, and therefore the character of the tent. One or two gives a simple shape. More gives a longer tent with a repeating rhythm of peaks. You set the count in Kingpole Configuration, along with the height in Pole Heights.
What is a side pole, and why are there different heights?
Side poles hold up the perimeter. Their height sets how much headroom you get at the edges and how steeply the fabric rises towards the peaks. The panel gives you Side Pole Height for the standard case, plus Low Height and Alternate Height. Alternating high and low side poles around the perimeter is a deliberate stretch tent look: it produces the wave along the edge that the style is known for, and it helps water run off at the low points rather than sitting on the edge.
What is a bale ring, and why does it drop?
A bale ring is the ring at the top of a kingpole that the fabric passes over. It is the same component, doing the same job, that sits on top of a pole tent kingpole. Without it, the pole would be a spike trying to push through the fabric at a single point. The ring spreads that push over a circle instead, so the fabric is not damaged. Bale Ring Drop sets how far the ring sits below the top of the pole, and Balering Diameter sets how big the circle is. A larger ring gives a softer, rounder peak. A smaller ring gives a sharper one.
What are guy lines, side guys and cross guys?
They are all ropes to the ground, doing the same basic job of stopping a pole from falling over, but from different places. This is common ground with pole tents: the guys are what actually hold the structure up in both, and the ground you need for them is the same problem in both. The two distance offset sliders in the Side Guys section control how far out from the pole the ropes are pegged. This matters practically: a rope pegged further out holds the pole better, but takes up more ground you may not have. If the tent has to fit a tight site, this is one of the first things you adjust.
What is an edge cable, and what is a catenary?
The edge cable runs along the perimeter from side pole to side pole, and the fabric edge follows it. A catenary is simply the curve a cable makes when it hangs under its own weight, the shape of a washing line. Every edge of a stretch tent is a catenary, curving inwards between the poles. This is not a defect to be straightened out. The curve is what keeps the fabric tight: a dead straight edge cannot hold tension.
What is sag, and why does it matter so much?
Sag is how deeply a cable curves between its supports. It is the single most important idea in this software, and it applies just as much to a pole tent as to a stretch tent. More sag means a deeper curve and a looser, more relaxed shape. Less sag means a flatter, tighter shape and much higher forces in the cable and at the poles. Pulling something almost flat requires enormous force, which is why the answer to a saggy looking tent is rarely to remove all the sag.
What is a ridge cable?
A ridge cable runs along the high line of the roof, from peak to peak. Ridge Cable Tension controls how tightly it is pulled and therefore how high and straight the ridge sits.
What are valley cables, and what are Lift 1 and Lift 2?
Valleys are the low lines between the peaks, the opposite of ridges. Valley cables control where those low lines sit. There are two, controlled independently: Lift 1 governs the valley between ridges, and Lift 2 governs the valley from a ridge to the end of the tent. Both run from -4.0 to 8.0. Raising a lift pulls that low line upwards, which is usually what you want if water is collecting there.
What is Arc Height and Arc Rotation?
The arcs are the curved perimeter connections between poles. Arc Height controls how far the arc rises. Arc Rotation turns the arc about its axis, which changes how the curve presents itself. Small changes here have a large effect on how the tent reads from the outside, and this is a control worth playing with once the structure is settled.
What is Corner Radius?
It rounds the corners of the plan rather than leaving them square. Stretch tents rarely have hard corners, because fabric does not naturally turn a right angle under tension.
What is the truss in Kingpole Configuration?
For larger tents a kingpole can be a fabricated truss rather than a single pole. The Arch Height, Truss Width, Truss Depth, Chord Box and Web Box controls describe that fabricated member. If you are designing a straightforward tent you can leave all of this alone.
Shaping the roof
What does Roof Tension do?
It sets how hard the roof is pulled overall, from 15.0 to 25.0, with 18.0 as the default. Higher tension gives tighter, flatter curves. Lower tension gives a softer, deeper shape. It also correctly affects the edge cable catenary sag, so raising tension tightens the perimeter arcs as well.
What is Edge Cable Ratio?
It scales the edge cable behaviour relative to the rest of the roof, letting the perimeter be tuned without disturbing the roof shape you have already found.
My roof looks flat and lifeless. What do I do?
Usually you have too much tension and too little sag, and the tent has lost its shape. Try lowering Roof Tension, increasing Catenary Sag, and checking that your kingpoles are tall enough relative to the side poles. A stretch tent needs a real height difference between its high and low points to look like anything at all.
What is ponding, and why does everyone worry about it?
Ponding is water collecting in a low spot on the roof instead of running off. It is the main thing that goes wrong with any fabric structure, pole tents very much included, and it is dangerous rather than merely untidy. Water is heavy. A pool that forms pushes the fabric down, which makes the pool deeper, which collects more water. That feedback is what brings tents down, and it happens overnight in the rain when nobody is watching.
How do I tell whether my design will pond?
Look at the low points and ask whether water at that spot has somewhere to go. The two statistics that matter most are Ridge Minimum Height, the lowest point along the ridge, and VC1 Mid Height, the mid-span height of the first valley cable. If a valley is sitting low and flat, water will find it. Raise Lift 1, raise the valley, or increase the height difference between the peaks and the low points, until every low point drains to an edge. Because the statistics are on the menubar, you can watch these figures while you drag the slider rather than checking afterwards.
So what makes a good stretch tent shape?
Strong height differences, no flat areas, and every low point draining to an edge. If it looks dramatic, it is usually working. If it looks flat and calm, it is usually not. That is not an aesthetic preference: the same curvature that makes the tent look good is what keeps the fabric tight and sheds the water.
The mesh
What is the mesh?
The mesh is the fabric of the roof, modelled as a grid of points. The software works out where every point settles once the tent is pulled tight, which is why the shape appears rather than being drawn by you. This is the one part of the model that is genuinely particular to a stretchy fabric. The poles, rings, cables and guys around it would be recognisable to anyone who has worked with pole tents.
There are seven mesh modes. Which one do I use?
The mesh mode is the model of how the fabric behaves. They are not quality levels, they are different materials and different densities:
Geometric 1, pure node averaging. The simplest and fastest.
Geometric 2, rubber sheet. A near-inextensible model that resists both stretching and compression. The Tightness slider controls how hard it is enforced. This is the workhorse and the one to use unless you have a reason not to.
Geometric 3, conveyor belt. Heavier and stiffer than rubber. Resists stretching strongly, compresses more easily.
Geometric 4, Laplacian averaging. An alternative smoothing approach.
Geometric 5, coarse mesh. Reduced density with clean corner triangulation. Fast, good while you are still moving things about.
Geometric 6, medium mesh. Around 0.7 m spacing, between coarse and rubber sheet.
Geometric 7, latex. Light, pulls itself tight, with a springy taut-balloon feel.
A reasonable habit is to design on a coarse mesh, because it responds quickly, and then switch to rubber sheet to see the real shape before you commit.
What is Form Finder?
It is a checkbox under Geometric 2 that shows the cables and rings only, with no fabric. It is genuinely useful for a beginner, because with the fabric hidden you can finally see the skeleton you have built and understand why the roof is doing what it is doing.
What does Geodesic Cables, Shorten, do?
It pulls the mesh down, from 0 to 10. It is a way of drawing the fabric in along a line rather than at a point.
Why does the model take a moment to settle after I move something?
Because it is genuinely recalculating where the fabric hangs, not redrawing a picture. Bigger changes take longer. If it looks wrong after a large change, press Regenerate Mesh.
The two builders
What are the builders for?
The main design mode gives you a rectangular tent described by numbers: a length, a width, a count of poles down each side. That covers most tents. The builders are for when it does not. Both open as a modal with a plan view of the tent, and in both you place the poles yourself by clicking, rather than describing them with numbers. When you are happy, one button turns your layout into a full three dimensional model, and you carry on in the normal way with the control panel.
What does the Stretch Tent Builder do?
It is a custom grid layout tool. You set a Length up to 80 m and a Width up to 60 m, and it draws a plan grid at one metre spacing. Every intersection on that grid is a node you can click. Border nodes, around the outside, become side poles. Numbered interior nodes, inside, become kingpoles. Clicking a node adds a pole there and lets you type its height. Clicking it again edits it. Nothing is placed until you place it, so you are drawing the pole layout directly on the plan.
Do I have to click every pole individually?
No, and you should not. The builder carries shortcuts for the patterns that come up constantly:
All side poles same height. Sets a single height across the whole perimeter, with the height typed alongside.
Per side, North, South, East and West. Sets a height for one edge at a time. This is how you get a tent that is high along the front and low at the back, which is a very common requirement when one side faces a view and the other faces a car park.
Every third side pole. Applies a height to every third pole around the perimeter. This is the shortcut for the alternating high and low edge that gives a stretch tent its wave.
Clear Selection. Empties the grid and starts again.
A running count of side poles and kingpoles is displayed as you work, so you can see the tent growing before you build it.
This infinitely variable builder allows the user to click on Tent Builder again and again to edit, for example "All sides down" usually with one side of the stretch tent in the air for access or two sides down etc.
Why would I use the Stretch Tent Builder rather than the main mode?
Because the site is an awkward shape, or because you want an irregular layout that a length and a width cannot express: a tent that steps around a building, poles at deliberately uneven heights, or kingpoles somewhere other than neatly down the centre line. If your tent is a plain rectangle, the main mode is quicker. If it is not, this is where to start.
What does the Round Tent Builder do?
It builds round and oval tents, which the rectangular controls cannot describe at all. Instead of a grid you give it a handful of numbers and it lays the poles out for you:
Side poles. How many poles around the perimeter, from 3 to 60, with 12 as the default. More poles gives a smoother curve.
Radius. The radius of the curved ends, from 2 m to 30 m.
Straight section. The length of straight run inserted between the two curved ends, up to 40 m. This is the control that decides the whole character of the tent, and it is worth understanding: leave it at zero and you get a true circle. Give it a length and the circle is cut in half and pulled apart, with a straight section dropped in the middle, producing an oval or racetrack shape. So one builder covers everything from a round tent to a long oval, from a single number.
Kingpoles on the X and Y axis. A count and a spacing for each axis, up to eight poles per axis. This places the peaks in the middle of the tent, which for a round tent is usually a single central kingpole and for an oval is usually a row down the long axis.
Once again it's possible to switch back and forth from the main modeller to the Builder to change, configure or rearrange all parameters.
Can I still adjust individual poles in the Round Tent Builder?
Yes. The plan view is clickable in the same way: click a pole to change its height individually, and the ones you have edited are shown in teal so you can see at a glance which poles you have touched and which are still at the default. Clear Selection returns everything to the default. As with the other builder, side pole and kingpole counts are displayed live.
What happens after I press Apply?
The builder closes and your layout becomes a real three dimensional model, with the fabric found over the poles you placed. From that point on it is an ordinary RTD Stretch model: the control panel, the mesh modes, the statistics, the exports and the undo history all work exactly as described elsewhere in this guide. The builder is a way of starting a design, not a separate kind of tent.
Working without fear
What happens if I break something?
Very little. There is full undo and redo across a hundred steps, autosave, and crash recovery if the browser closes unexpectedly. Camera movement is deliberately kept out of the undo history, so orbiting the model never costs you a step of real work. Explore freely. This is the most important thing to understand as a beginner: you cannot ruin the model.
What is the difference between Save State and Save RTD Model?
Save State takes a named snapshot inside the current session, and View States lists them and brings any of them back. Use it to compare options: three roof shapes for one client, side by side, rather than overwriting one at a time.
Save RTD Model writes a model file to disk, which Load RTD Model reads back. This is the one that survives closing the software.
The short version: Save State is for comparing ideas today, Save RTD Model is for keeping the design.
What are Project Details for?
Project, Client and Job Number travel with the model rather than living in the filename. Once a Job Number is set, every file the software writes is prefixed with it automatically, including the PDF report, DXF, seating plan, guest list, place cards and fire compliance report. It sounds like housekeeping. It stops the wrong drawing reaching the wrong client.
Can I work in feet?
The Units button switches the Statistics readouts between metric and feet, and remembers your choice. Be clear about what this does and does not do: it changes the displayed statistics only. The model, every box you can type in, and every DXF export stay in metres, always. Metric is the source of truth, so the imperial view can never drift out of step or contaminate a drawing.
Getting work out
What is DXF, and why does it matter?
DXF is the general drawing format that the CAD and fabrication chain expects, and it is how the geometry you have designed reaches the people who will make and erect the tent. It is always written in metres.
What are the mesh exports for?
Collada, OBJ, glTF and STL are for visualisation and downstream modelling, feeding rendering packages, game engines and 3D printing. They are how the tent gets into a pretty picture. They are not fabrication files. Collada imports into software like SketchUp, OBJ into Solidworks, glTF into Blender, SketchUp or Rhino.
What paperwork can it produce?
A PDF tent report, a fire compliance report, and from the Seating Planner an entrance guest list and printed place cards. All are prefixed with the job number.
What are the Site Planner and Seating Planner?
The Site Planner places the tent on the site, and can import previously saved RTD models so several structures can be laid out together. The Seating Planner lays out the interior. Both export to DXF.
Where do the files go?
Wherever you set with Define Project Folder.
Practical matters
Can I use this on a tablet?
Yes, and it is built with that in mind. The Display dropdown puts the whole visibility set one tap away without scrolling the panel, and errors appear as a message on screen rather than hiding in developer tools you cannot open on a tablet.
How do I see inside the tent, or show it to a client?
The View menu has Interior View to put the camera inside, Worms Eye View for the approach a guest gets, and Birds Eye View for the context. Insert Background places a photograph of the actual site behind the model, and Save Current View as Image captures what you are looking at. The Display menu changes the roof colour, with eight to choose from, and the roof transparency.
What are the eleven figures in the Stats menu?
Overall Length and Width, Surface Area, which is the fabric, and Floor Area, which is the ground covered, Average Height, Side Pole Height, Kingpole Height, Bale Ring Height, VC1 Mid Height, Ridge Minimum Height and Kingpole Spacing. Surface Area is what you buy. Floor Area is what you sell. Ridge Minimum Height and VC1 Mid Height are what keep you out of trouble.
How do I know when the design is finished?
When the shape has real height variation and no flat areas, every low point drains to an edge, the tent fits the site with its guys pegged where there is actually ground, and the statistics are numbers you are willing to put your name to. Then export.
One last thing to remember?
What the disclaimer at the start of this guide said. RTD Stretch warrants one thing, that the model is geometrically accurate. It does not warrant that the shape is a good one. The choice of shape, of high and low points, and of pole configuration is yours, and RTD will draw a non-optimal tent as faithfully as an optimal one. It will also draw a tent that is beautiful, drains perfectly, and is still the wrong thing to put up on an exposed site in November. Whether a structure is safe to erect, in a particular place, in particular weather, is not a question this software answers. That judgement remains yours and your engineers. Use RTD for conceptual design, for the accurate model, and for showing a client the tent on their own site. Then have it checked.
