Guides > Altitude Readings

Introduction

This guide is about building a quality 1 barometer (yes, the worst possible ones) and will tell you how to get altitude readings with a precision of 1 inch.

The correction table improves accuracy, not precision. As the quality increases, precision increases. That is, if you stand in the same spot and take a reading every minute with a 1 and then a 9999 the spread will be smaller than with the 9999 one. Accuracy is getting the right number, not having consistent numbers. Do all barometers give the same altitude in a certain spot at 12PM? If that is the case, I think we could assume that the numbers are accurate aswell. -Dio

Details about barometers and facts are at the bottom of this page.

Poor english alert ! You have been warned !

Building a Quality 1 barometer

You will need :

• 3 Barometric Spheres of Quality 1
• 1 Lead
• 1 Glass pipe
• 1 Water in jugs (the jug is consumed)

You will get Quality 1 Barometric Spheres from your Glory hole (at a cost of 1 Glass rod each) by Unloading your creation right after starting it, without any pull/push/blow/whatever. No skill in using the Glory hole itself is needed at all.

Using the "Special project..." menu from the glory hole, you can then craft your brand new "barometer: Quality 1".

Reading your current altitude

When you have a barometer in your inventory, a new "Measure Altitude" item appear in your Special menu. When used, a message in Main will tell you what altitude your barometer believes you currently are at.

Depending of the time of the day, a quality 1 barometer can be up off by up to 5 feet, so we need to correct the error.

To do so, you will need : the precise time the reading was done at, and either a correction table, a spreadsheet or a Javascript page.

BEWARE : Barometers shows negative readings as 0'0". If your reading is 0'0", you have a bad reading and can't compute real altitude (check back between 12PM and 12AM to be assured not to get negative readings).

Precise time

I do use the clock toggle by the /clock command

Correction table

It's available in Acrobat reader's PDF format : Barometer_correction.pdf

This works only with a barometer of quality 1

Spreadsheet

It's available in Excel format : Barometer_correction.xls

This currently works only with a barometer of quality 1

Javascript page

It's available at this page.

This currently works only with a barometer of quality 1

Facts about barometers

Barometers' readings suffers from an error linked to their quality and the time of day, there is no random factor.

All barometers gives perfect readings at 12PM and 12AM, worst ones at 6AM and 6PM.

The formula is :

Error = SIN( Minutes since 12PM / (24*60) *2*Pi)* Maximal error

The maximal error for a quality 1 barometers is of 5' (aka 60 inches).

I'm still looking at the formula giving max error from quality. A Q5628 barometer have a maximal error of 40 inches. (Need more raw data)

How to Calibrate a Barometer

To calibrate a barometer, stand in shallow water at 6:00 AM game time. The reading will be the maximum error value for that barometer. The formula is somewhere around 215 Quality Points per Inch, but we need more data to nail down the exact formula and the boundry conditions (other than quality 1 = the maximum error of 60 inches), Using a lookup table works just fine for the moment. {MarvL}

Aqueduct Survey Spreadsheet

The above formula has been extended into an Aqueduct Survey tool that supports field surveys, corrects the readings for the time of day errors for multiple calibrated barometers, calculates the height of the tower that will be required to support an Aqueduct Pipe at that location, and automatically prepares a table that you can cut and paste directly into a Wiki Page, to drive a map.

Aquaduct_Survey.xls, is attached to this page and available as a download, is an Excel Workbook. See the Keyhole Lake page for an working example. Contact MarvL in game if you have questions or suggestions about the survey tool.

Instructions

There's no need to calibrate your barometer ahead of time, just go ahead and use it and record the readings. Calibrate your barometer by standing in shallow water at 6:00 AM game time, and then plug the Barometer Quality and the Maximum Error into the lookup table. Presto! Instant results. The spreadsheet is set up to accept only exact barometer quality matches, maybe we'll have a good formula someday, so you don't even need to sort the lookup table except for appearance.

Grid

If you plug in the value of the northwest tower location, the spreadsheet will automatically calculate the coordinates of the related towers to the east and south.

As indicated on The Test of Life page, Towers are constrained to a hexagonal grid with 320 foot (20 coordinate) edges. You can go directly horizontal, in 20 coordinate increments, or you can go diagonally at 60 degrees. but you can't go directly vertical. The horizontal tower spacing is 20 coordinates and alternate rows are staggered by 10 coordinates. Vertically the rows are separated by 10 * Sqrt(3) or 20 * sin(60) as you prefer.

An empty grid is a very handy means of recording your field data.

A grid with the required tower heights typed in is a very good way to document your anticipated route.

Correction

This is the sheet that does all the work. You can use any arbitrary mix of barometers, so long as they have been calibrated and entered in the lookup table. The spreadsheet is designed so that you can consolidate field data from various field crews, each with a different quality barometer.

Once you have a probable route in mind, work backwards from your most distant tower location and add 5 feet for each pipe segment to determine the pipe height for the next tower and, ultimately, the pumping station. If alternate routes are available, simply calculate them both until they arrive at a common point to see if there's a difference in the required pipe elevation. The route with the lowest base elevations isn't likely to be cheapest route because of the height adn cost of the required towers.

Your cheapest route will very likely follow the contour lines in the region, and should take full advantage of any hills, expecially hills near the pumping station. Note that zigzagging will raise the pump height that will be needed to reach a given tower location.

Wiki

Here's the wonderful part. Once you've prepared the Correction page you can cut and paste the data directly from the Wiki tab into your own Wiki page, and you'll have a nice map of your route that anyone can easily review.

You can create your own backgound map, if a suitable one isn't already available, by following the instructons at Location Maps.