Daily Challenge Day 40

Went to site to get some levels. Took dumpy level, unfortunately the 3m staff we have wasn’t long enough. But no problem: we had a 1200mm long spirit level. So we incrementally checked the drop, for each 1200mm run. We could have probably used the 3m staff, with several change over stations, but we were racing against a rising tide. Still we did manage to take a string of spot levels, at a low level and at a higher level, and these are nominally linked. So just have to draw up some sectional profiles.

It reminded me of school geography, where we used two sticks of equal length connected by string. I’m not sure but I think we also used a geoliner, which was used to measure the angle between the vertical sticks and the string. We profiled the West Lakes primary and secondary dune system. At another time we camped on the banks of the Murray River near Renmark, and used compass to map the path of an oxbow lake. The lake was intermittent and dry at the time, still the objective was to assume it was full of water and the other side was not accessible, therefore had to map from one side only.

Today we used a dumpy level (optical). It has tacheometric cross hairs, and protractor base. So besides taking levels, the protractor base can be used to take relative bearings, whilst the tacheometric cross hairs are used to determine distance. Its a more general purpose tool than a theodolite.

Whilst education in mechanical typically does not include the use of a dumpy level, we do however make use of similar tools such as an autocollimator along with triangular prisms to check the straightness and flatness of tool beds. Whilst I otherwise grew up around the use of dumpy levels. When I did industrial experience, I assisted with the installation of a new CNC boring machine, for which they used a dumpy level and a vernier height gauge for leveling the machine bed. So given the versatility of a dumpy level, and the existence of large machine structures,  probably beneficial to include use of a dumpy level in the mechanical engineering education at all levels (technician through engineer).

Back to todays survey, I was expecting that the nearest permanent survey mark would be several kilometres away, but found a metal plate nailed to a kerb, on site, indicating a mark was 0.3m way, where there was a simple nail or pin. So hopefully from this can get the necessary information for conversion of levels to the Australian Height Datum.

After did our simple survey, I switched my mobile phone on to check emails, to identify had no signal. So not only is my mobile phone typically switched off whilst working, chances are that if I am not working at home or the office, then I am on site, and that site does not have mobile phone access. Whilst I understand it takes longer to write an email, it takes less time to read an email than it does to listen to a voice message. Writing also requires more thought, so with respect to most people writing a fax or email usually permits them to solve their own problem: or ensure they provide me with adequate information so that I can reply with a solution rather than a series of questions.

Writing and sketching help define and then solve problems. Two thirds of an answer lies in putting the question clearly. The best way to get a question clear is to put it in writing, and then read it and question it, and then rewrite it, and repeat until the question is seemingly unambiguous.

Similar applies to sketching. With sketching need to check have adequate dimensions so that someone else can replicate the defined shape and required size. If cannot replicate the shape and size then have inadequate dimensions. One simple approach to check is to triangulate the dimensions. For example three angles in a triangle can define its shape but not its size. Whilst three dimensions and no angles defines size and shape. Angles are typically difficult to measure and set, so it is typically preferred that angles are avoided. So angles typically defined by rise and run, which assumes can form a right angle. In an engineering workshop have precision flat mark out tables (apparently called surface plate), and vernier height gauges.

Another useful tool I learnt about a few years back whilst following engineers without borders on twitter, is the Abney level. This is basically a more refined version of using a geoliner and plumb bob to determine elevations or heights or objects. The abney level can be used with a support pole or without. It is a convenient device for hikers to carry, and typically used by park rangers and foresters.

So an abney level, a directional compass (magnetic), and pedometer are useful for some rough mapping and surveying. Though a measuring wheel is better than a pedometer it’s not as convenient to carry. Getting a rough estimate of walking speed and measuring trip time is probably just as accurate as a pedometer: given false step counting of a pedometer.

An alternative for measuring distance is to use a directional compass and known length of a base line, then use trigonometry to calculate forward distances. The method adopted all depends on needs and convenience of the task at hand.

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