Surveying with the CL900

Tablet PCs come and tablet PCs go but the problem of the field PC remains the same. What we need is a reliable, daylight readable and portable device that will run CAD all day long so that we can see what we are doing as we do it. Not much to ask, and as the tablet wars hot up things should be getting better for the practitioner.My workhorse is the Motion Le1600 which will run most of what I need, will power up all day long on 3 batteries and has a just about daylight readable screen.

We have been friends for years. We get on. There is nothing wrong with it, its a great teaching tool, but it’s too long in the tooth to hold up AutoCAD 2012 or Windows 7 so well…and it’s starting to feel heavy compared to some of the newer kit that’s begining to appear. Its logical replacement is the Motion J3500 but, being of reduced means, I have decided to look at what can be done at the budget ‘netbook’ end of the market and this is where I met the remarkable CL900.

Suddenly, after using these things for years, there is a rash of apparently cheap Android/ Ios/HP OS tablets available on any high street (well retail park anyway) for well less than a grand. Having tried to do something useful with the beguiling iPad I feel I have learnt the ‘if it isn’t Windows…. it isn’t Windows’ (or to put it another way if you can’t run proper CAD on it it’s an expensive door stop) lesson the hard way. A quick look at what you can run on an Android unit and the lovely cheapness doesn’t look so good.So if I have to lug a tablet around the world (and believe me, I do) what do I expect it to do?

The essentials are CAD, Bluetooth, Serial Comms (USB or Dsub9) email and internet, I also need to be able to write reports, read and write PDF, handle images to a degree (more on this later) and present PowerPoints. It may well be madness to expect the Intel Atom (even at 1.5Ghz with 2GB of ram?) platform to manage all this so let’s start with getting to grips with CAD on a netbook- can it work?

With only 1.5Ghz prosessing speed and a max of 2GB ram you would think any current release of CAD (they only get bigger and slower don’t they!) would be a non-starter on the CL900- but if all you neeed to do is build wireframes and line drawings current release BricsCAD v10/11 holds up well ( yes it’s a bit slow to start…nothing new there!) and so I’m all set to find out if it will do a good days work.

As you would expect with a light weight processor and solid state HD package power uptake is good and the battery warnings don’t begin to bleat until at least 8 hours runtime!

3 stations and 1137 points plotted into CAD and 49% battery left on its first field day is a very good result…I’m begining to like this!

The battery life for field survey is very good indeed. We did a full days worth and didn’t need to deploy the external battery pack: with a Powerbank MP3450 a comfortable 10 hours runtime should be easily achievable.

The outdoors screen view is ok, its not the best but its workable. CAD runs ok if you accept its going to be a bit laggy with regens, opening up and the obvious graphics grief with image files.

Now the other stuff I want it to do….

I can’t expect this little chip to push photos around in Photoshop so I have installed ‘Advanced JPEG Compressor’ to get the basics of crop and web-ready done. It’s very efective and reasonably priced too.

Writing reports is just about doable in Word (the old hardware of keyboard & mouse wins really and the single USB port is a bit of a handicap here).

Camtech supplied the CL900 and are most helpful with technical support so far (which has involved testing removal of the Ntrig interface for me: a potentially risky manoeuvre in the 1st instance).

So if you want a field tabet that will run TheoLt all day long the Motion CL900 is a good bet, its not lightning fast but it does the job. It’s light, well made and is a good example of a ‘Windows ipad’ (aWipad?) -Steve Job’s legacy may yet be a wide acceptance of the tablet form-something I believe needs to be a bit more than a locked down content browser, the CL900 isn’t quite an ipad for windows but its very close.

More information on the CL900 is here

Photography for PhoToPlan3D: the 3×3 rules

The following text is adapted from a paper presented by Peter Waldhäusl (University of Technology, Vienna, Austria) and Cliff Ogleby (Dept. of Geomatics, University of Melbourne, Australia), at the ISPRS Commission V Symposium “Close Range Techniques and Machine Vision” in Melbourne, Australia, 1994. Simple rules that are to be observed for photography with non-metric cameras have been written, tested and published at the CIPA Symposium in Sofia in 1988.

1 – THE 3 GEOMETRIC RULES
1.1- CONTROL
• Measure some long distances between well-defined points.
• Define a minimum of one vertical distance (either using plumb line or vertical features on the building) and one horizontal.
• Do this on all sides of the building for control.
• Ideally, establish a network of 3D co-ordinated targets or points.

1.2- WIDE AREA STEREO PHOTOCOVER
• Take a ‘ring’ of pictures around the subject with an overlap of greater than 50%.
• Take shots from a height about half way up the subject, if possible.
• Include the context or setting: ground line, skyline etc.
• At each corner of the subject take a photo covering the two adjacent sides.
• Include the roof, if possible.
• No image should lack overlap.
• Add orthogonal, full façade shots for an overview and rectification.

1.3- DETAIL STEREO PHOTOCOVER
Stereo-pairs should be taken:
• Normal case (base-distance-ratio 1:4 to 1: 15), and/or
• Convergent case (base-distance-ratio 1:10 to 1: 15).
• Avoid the divergent case.
• Add close-up square on stereo-pairs for detail and measure control distances for them or place a scale bar in the view. Check photography overlaps at least 60%.
• If in doubt, add more shots and measured distances for any potentially obscured areas.
• Make sure enough control (at least 4 points) is visible in the stereo image area and at least 9 control piubnts in the single image area.

2 – THE 3 CAMERA RULES
2.1 – CAMERA PROPERTIES
• Fixed optics if possible. No zooming! Fully zoom-out, or fix the focus using adhesive tape or avoid zoom optics altogether. Do not use shift optics. Disable auto-focus
• Fixed focus distance. Fix at infinity, or a mean distance using adhesive tape, but only use one distance for the ‘ring’-photography and one distance for close-ups.
• The image format frame of the camera must be sharply visible on the images and have good contrast.
• The true documents are the original negatives or digital ‘RAW’ equivalents. Use a camera with a highest quality format setting.

2.2 – CAMERA CALIBRATION
Use the best quality, highest resolution and largest format camera available:
• A wide-angle lens is better than narrow angle for all round photography. Very wide-angle lenses should be avoided.
• Medium format is better than small format.
• Calibrated cameras are better than not calibrated.
• Standard calibration information is needed for each camera/lens combination and each focus setting used.
• A standardised colour chart should be used.

2.3 – IMAGE EXPOSURE
Consistent exposure and coverage is required.
• Work with consistent illumination: beware deep dark shadows!
• Plan for the best time of day
• Use a tripod and cable release/remote control to get sharp images.
• Optimise shutter speed and aperture by using a ‘slow’ ISO setting ..
• Use RAW or ‘high quality’ or ‘fine’/’super fine’ setting on digital cameras.
• Test and check the exposure using the histogram to understand the balance needed.

3 – THE 3 PROCEDURAL RULES
3.1 – RECORD SITE, CONTROL & PHOTO LAYOUT
Make proper witnessing diagrams of:
• The ground plan with the direction of north indicated
• The elevations of each façade (1:100 – 1: 500 scale). Show the location of the measured control points.
• Photo locations and directions (with frame number).
• Single photo coverage and stereo coverage.
• Control point locations, distances and plumb-lines.

3.2 – LOG THE METADATA
Include the following:
• Site name, location and geo-reference, owner’s name and address.
• Date, weather and personnel. Client, commissioning body, artists, architects, permissions, obligations, etc.
• Cameras, optics, focus and distance settings.
• Calibration report, if available.
• Description of place, site, history, bibliography etc.
• Remember to document the process as you go.

3.3 – ARCHIVE
Data must be complete, stable, safe and accessible:
• Check completeness and correctness before leaving the site.
• Save images to a reliable site off the camera.
• Save RAW formats to convert into standard TIFFs. Remember a CD is not forever!
• Write down everything immediately.
• Don’t crop any of the images – use the full format.
• Ensure the original and copies of the control data, site diagrams and images are kept together at separate sites.

Although these rules were devised for ‘classical’ (stereo) phtogrammetic recording they hold true for photocover in general. The rules have been modified to suit digital camera work and have not incorporated the use of the Exif data in processing the images.