This post was written with the help of Greg Tucker of the BSR, who is our new project CAD developer.

The new drawing workflow is working better than expected with TouchDraw’s unlimited paper size and ridiculous zoom levels. The iPad drawings this summer are produced directly on top of the AutoCAD files instead of being traced. This gives us an almost-spatially-correct drawing environment. Almost because we do use a local coordinate system which we have chosen to ignore in TouchDraw. So while the measurements are 1:1, the plan is not in the local grid, and as you will see below, north has changed.

The overview of the process is that the relevant area is exported from AutoCAD in svg format, opened up in TouchDraw, and then cleaned up and made ready for field drawings. Once the drawings are finished, they are again exported to svg, converted from svg to dwf using Inkscape and then back into AutoCAD. There are some minor adjustments to be made in AutoCAD to get the drawing to fit back into the spatial grid.

Here are the details:

Creating SVG files for TouchDraw (And reintegrating them with the CAD model)

This season we’ve decided to draw on the iPads in the field using TouchDraw, which can export in Scalable Vector Graphic (SVG) format. This makes integration of the drawings into the CAD model much quicker, just needing to assign layers to the features and drawing elements as opposed to digitizing either raster images or on a drawing tablet. Our site plan is being made using AutoCAD, which unfortunately does not recognize SVG for either import or export (as of the 2012 version).

The first step to drawing on site was to export a base plan of the trenches so that the excavators could begin planning directly on their iPads. After exploring a few options available we decided on DWG to SVG Converter 2011 MX by DWG Tool Software to create SVGs from the CAD models. Initially all our attempts to generate the baseplans for each of the four trenches resulted in files approaching 10MB, much too large to easily and quickly manipulate. Even when deselecting layers we didn’t want exported, deleting hidden lines, changing the compression, etc, the file sizes remained at this bloated level. The immediate solution we have been implementing is to copy the objects necessary for each of the baseplans (wall bases, architecture, trench extents, baselines, and four target points to ease with scaling and rotation) to a new DWG so as to remove the extraneous data. In the options menu in the DWG to SVG converter we select “Last Saved View” and adjust the output size to match the view dimensions in the CAD model. If we are viewing plan of trench 53000 for instance the dimensions of the view window could be 26.55×11.62m and the image size we would output would be 2655×1162. The resulting SVG has a scale of 1px:1cm and is small enough, <500kb, to be easily manipulated in TouchDraw. Additionally, to aid drawing in the field the CAD model is rotated so that the baselines are aligned vertically before SVG creation. The final output then allows the excavators to use the gridlines within TouchDraw to draw more quickly and efficiently.

After the excavators draw their plans the resulting SVGs are loaded in Inkscape, which is compatible with both SVG and DXF, and saved as a DXF. The DXF can then be opened by AutoCAD, the objects can be rotated and scaled quite quickly using the target points and then copied into the side plan DWG.

There are potentially ways to streamline this process even further and we will be exploring different methodologies throughout the season.

output from CAD for trench 56000

Once the svg file is exported from AutoCAD, it is transferred to TouchDraw via iTunes. In TouchDraw there is an import command to convert the drawing to their native format.

Objects in the drawings were pulled out of the flat svg file into their different layers in TouchDraw and assigned our more standard drawing conventions (orange dashed line for the trench outline and blue dashed line for the baseline, etc.).

Plan with layers in TouchDraw.


The final drawing is given a name to indicate that it is the baseplan. That is, you do not open this one and start drawing. This one is duplicated and the resulting file named “trenchnumber plan x”

When the drawings are finished, they are saved in the native TouchDraw format. Then the Walls, Trench Outline, and Scalebar layers are turned off. The plan is exported into svg format with only the registration points, baseline, and any features or SUs drawn in. The resulting file is given to the architect for importing into the CAD plan.

The native svg output and TouchDraw files can be downloaded from here.

This is also my first post from the iPad. I am testing blogsy.

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