Pei Zhan is ceo of Arctuition, a brand-new app development company that is thinking about how the next generation of mobile CAD should work. Before starting out on his own, he was a principal software engineer who worked on AutoCAD at Autodesk. He left at the beginning of 2013, dabbled in a few projects, and then last October settled on writing a mobile CAD app. The result is ArcSite for iPad, which had its formal unveiling at a TechCrunch event just four months ago. (See figure 1.)
 Figure 1ArcSite recognizing a roughly-drawn shape as an arc, and applying constraints in real-time
"Our vision is that mobile CAD should be fundamentally different from desktop CAD. Keyboards and mice are awkward for graphics input: think about how many interactions are required just to define an arc; touchscreens are perfect for CAD as they mimic the natural way of drawing with pen and paper," he wrote in his initial email to me.
ArcSite is unique among mobileCAD apps, because it employs the following technologies at the same time, in real-time:
- Shape recognition straightens out hand-drawn sketches as lines and arcs
- Constraint solver sets the exact angle and length dimensions
He makes the claim that his company's shape recognition technology is significantly better in its recognition rate than competitors, and that it is the only program doing it in real time. As we sketch a shape, the engine analyzes the input strokes in real time and then comes up with a recognition result (line or arc). The lines and arcs appear in the drawing as we draw.
To learn more about the thinking that went into ArcSite, I interviewed Mr Zhan by Skype.
Q&A
Grabowski: Were constraints designed in from the beginning? Zhan: No, not the constraints. At the beginning, we worked on getting the input strokes recognized as lines and arcs. The constraint solver was implemented later after we realized that shape recognition alone doesn't bring about the desired accuracy. For example, it is easy to draw a straight line at a rough length, but it is very difficult to draw it to an exact length like 9.1mm. The constraint solver was the missing piece required to create drawings accurate enough for CAD users.
Grabowski: Was it difficult to write a constraint engine for iOS? Zhan: Neither shape recognition nor constraint solving is particular to any specific platform. Even though our app is available only on iOS for now, we could port it to other platforms pretty easily; the technologies themselves are cross-platform.
As for the difficulty, reliably recognizing people's freehand input as lines and arcs challenged us. Before we arrived at our proprietary algorithm, shape recognition was considered immature. Most shape recognition technologies have a low recognition rate, especially where arcs are involved. We believe our recognition engine has the best recognition rate so far, and is the first one to do it in real time.
Constraint engines are different. They are already an advanced technology, and there are very good open source and commercial solutions around, like D-Cube's DCM.
Grabowski: Did you license any libraries for it? Zhan: We did license some open source code, but have not licensed any commercial components so far.
Grabowski: I wondered if it would be possible to put a second finger on the screen while drawing, kind of like holding down the Shift or Ctrl key in desktop CAD, to do things like toggle ortho or snap mode. Would iOS recognize this?
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Zhan: Oh, yes. Right now when you put a finger on the screen, ArcSite changes to Control mode, which lets you adjust the endpoints of the arc, to make it easier to snap to any other point.
Grabowski: To insert a PDF, I first had to upload the file to your Web site, and then I could access it with ArcSite. Why did you take this approach? Zhan: It was a business decision to get people to access our Web site. But you can also access PDF files through Dropbox: just go to the Dropbox app on the iPad, select the PDF file, choose Open As, and then pick ArcSite as the destination. When exporting a drawing, users can choose to export to local folder or else email the file.
Grabowski: How about supporting sensors in iPads? Zhan: GPS is a great sensor to have. But as for tilt and the other ones, we don't want to make it too complex, or to confuse the users in different scenarios. One of the biggest challenges is to keep the app user-friendly. Most desktop CAD systems require users to train for weeks and even months, which is not an ideal situation.
Grabowski: What about Android? Zhan: There is too much variety in Androids, and so we started with iOS; it was pretty easy to pick up. Right now we don't even support iPhone, because we wanted to make sure that the user experience is good enough. So, iPhone next, then either Android or Windows tablets; we haven't decided which to do next.
Grabowski: What file format does ArcSite use? Zhan: It is our own native format, and it can be exported to any other format. Right now we support DXF (which we got through an open source project), PDF, and [raster] PNG. Theoretically our format can be exported to any other format.
Grabowski: Importing drawings? Zhan: We are not considering importing any CAD files, because it is unlikely our kinds of users would start with CAD drawings. We see them starting from scratch or with a PDF or an image. ArcSite is for conceptual design, not detail design. We could add import in the future if users wanted it.
Grabowski: 3D? Zhan: Touchscreen input is perfect for 2D drawing input, as it resembles pen and paper in many ways. As for 3D, I don't see any advantage to using a touchscreen over a keyboard and mouse -- at least with existing history-based 3D modeling methods. So for now we will just focus on 2D and will only move to 3D when we feel ready.
Grabowski: Handwriting recognition? Zhan: Not our strong suit. We spend our time at shape recognition. There are algorithms for hand writing, but we have not yet figured out how to seamlessly integrate it. I would love to add it, if it could distinguish between a user drawing shapes and text. Even so, handwriting algorithms are not yet optimal.
Let me explain: we feel that handwriting recognition is a nice-to-have feature, but not a must-have. Keyboards already are a good alternative as people type a lot faster than write by hand. On the other hand, shape recognition carries a lot more weight in drawing apps as it significantly improves usability and speed. The traditional ways of shape input, mostly originally designed based on the keyboard and mouse with desktop computer, are awkward, and even more so with a touch-only device.
Grabowski: Who do you find is taking up your product? Zhan: So far our app has been used by a lot of contractors who are doing building renovation, such as carpenters. Some designers and landscape architects as well, because they need to go into the field to do site investigations. Our app is a good alternative to pen and paper, and to desktop programs running on tablets, as they were not designed for tablet use.
Grabowski: What about your future direction for this app? Zhan: I want to add more CAD-like functions, but we are also working on cloud-related features. The focus for the next month is to add collaboration and sharing features. I like to call it "mobile-cloudCAD."
One new feature coming is the ability to trace over a picture or PDF; many users have been asking for this. Tracing is done by the user, but our software figures out the shape and recognizes the geometry. Also, we are considering adding support for styluses, as some come with great features like palm rejection and pressure sensitivity. These functions could potentially improve the user experience.
Grabowski: In addition to a free mode, your pricing model consists of monthly and annual subscriptions in three tiers [$10/month and up]. Why this approach? Zhan: We need to have a subscription model, because it will help fund us in developing the app to have more features. I would not consider a one-time purchase at this time, as it doesn't make for a sustainable business. App stores require us to provide lifetime free updates, so we need to subscription model for now.
Grabowski: Where did the ArcSite name come from? Zhan: Originally, we designed ArcSite as a tool for site investigation, for inputting data in the field. Our target users are those kinds of professionals, especially in building renovation. We hope to widen the audience to office workers who need to make basic designs.
www.arcsiteapp.com
Walkthough
I tested ArcSite on an iPad using the free version downloaded from Apple's app store. (See figure 2.) You can see my illustrated walkthrough on the WorldCAD Access blog: worldcadaccess.com/blog/2015/08/guided-tour-through-arcsite-.html
Figure 2 Editing glyphs near a selected entity
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