Windmill Software Ltd
Data Acquisition Intelligence

fluorescence mapping GIS
March 2002

The Newsletter for PC-Based Data Acquisition and Control
Issue 44          March 2002
--------------------ISSN 1472-0221----------------------

In the Northern Hemisphere, the 21st of March marks the 
beginning of Spring. A time when night and day are 
nearly the same length. Today we try to shed light on 
data acquisition in Geographical Information 
Systems, highlighting how automatic collection of data 
can save time and money. Plus, we resume our Excel 
corner series.

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subscribed - should you wish to cancel your free 
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* Windmill News: Mapping Dye Fluorescence in Coastal 
* Geographical Information Systems and Data Acquisition
  - Acquiring Data
  - GIS: A Decision-Making Tool
  - Low-Cost GIS Applications
* Excel Corner

Windmill News: 
Mapping Dye Fluorescence in Coastal Waters

Marine scientists in New Zealand are studying the 
dispersion and dilution of sewage in coastal waters. 
They release a stable, non-toxic, dye immediately 
downstream of the effluent outfall pump, then use a GPS 
receiver and fluorometer to monitor: the position of the 
boat they are in, dye fluorescence and temperature. To 
capture this data to the PC they are using Windmill 4.3 
software, which is free to Monitor subscribers.

The GPS and fluorometer are connected to a Notebook 
computer's RS232 (COM) port. Windmill saves all the 
readings to a single text file, time stamping each data 
set. The sampling interval varies depending on location, 
and ranges from one reading per second to one reading 
every five seconds. This system enables real-time 
measurement of the position, fluorescence and 
temperature in the receiving water. After collecting the 
data, they develop a map of dilution within the effluent 
plume using a Geographic Information System 
software package (Arcview 3.2).

The scientists have used the system on other outfalls, 
and for other applications. For example, using the same 
setup but with the fluorometer calibrated to a different 
wavelength, they've measured the in-situ depletion of 
chlorophyll-a in the water column downstream of mussel 

For more information on this system see


Our thanks to the Cawthron Institute for their help with 
this article. They are a private, independent, 
not-for-profit research centre which has been operating 
in New Zealand for 82 years. Their purpose is to 
benefit the region through science and technology, 
especially the aquaculture of shellfish and seaweeds, 
biosecurity issues, marine and freshwater science, and 
analytical chemistry and microbiology.


Geographical Information Systems (GIS)

The term Geographical Information System was coined by 
Roger Tomlinson in the 1960s. He realised that computers 
could be used to map and analyse the vast quantities of 
data that were then being collected by the Canada Land 
Inventory. However, it wasn't until the 1990's advances 
in personal computers, that GIS became more widely 
available to individual scientists, engineers and 
planners. During this decade article started to be 
published in technical magazines highlighting 
applications for GIS. For example, for mobile test and 
measurement, search and recovery of lost objects on the 
seafloor, habitat delineation and soil fertility mapping.

The diverse applications all have in common the 
fundamental properties of a GIS. That is a computer 
running software capable of assembling, storing and 
displaying data identified according to its location. In 
fact, a GIS is a special case of a data acquisition system.

Acquiring Data

Like many DAQ systems, a GIS needs to assimilate data 
from many different sources, to store and to analyse 
the data. A GIS, though, always references "attribute" 
data (such as temperature, fluorescence or biodiversity) 
to "spatial" data (such as latitude and longitude). 
Sources of spatial data include digitised charts and, 
as highlighted in our Windmill News section above, co-
ordinates automatically collected from GPS receivers. 

Sources of attribute data include sensors and 
instruments connected to a PC as in other data 
acquisition applications. Alternatively, some attribute 
data - such as information from videos - may need to be 
entered into the system by hand. In all cases attribute 
data needs to be linked to the spatial data. When data 
is collected from GPS receivers and PC-linked 
instruments, this is automatically achieved as all data 
can be logged to the same date- and time-stamped file. 
Video evidence, for example, can be later added to the 
file using the time as a reference.

GIS: A Decision-Making Tool for Scientists, Engineers 
and Planners

The prime objective of a GIS is to be a decision-making 
tool. A useful, and often essential, aid to planning and 
condition assessment. It uniquely links different sets 
of data. The data can be presented as tables, graphs, 
maps or 3-dimensional images. Of course, careful 
planning is required before implementing a GIS. Not just 
of what data needs to be collected and how it should be 
analysed, but of how close together the samples need to 
be taken. For mobile applications in boats, trains, 
vehicles, etc, where readings are automatically logged, 
this translates to sampling speed. Too slow and 
precision diminishes, too fast and excess data 
needlessly occupy valuable storage space.

Low-Cost GIS Applications
For a simple, low-cost, GIS application where data is 
automatically collected - you need:
- A Computer
- Software like Windmill to simultaneously collect 
  spatial and attribute data and pass these to Windows 
  mapping and analysis software
- A GPS receiver and other instruments or sensors to 
  collect spatial and attribute data
- Mapping or analysis software

Monitor subscribers can download Windmill for free. 
This lets you automatically acquire data from GPS 
receivers and other instruments with RS232 ports. 
Windmill, however, is not limited to RS232 
communications. It can also handle GPIB, Ethernet, USB, 
RS485, RS422, Modbus and ISA-bus devices. However, in 
these cases the instrument driver is not free and costs 
£145 (around US$210 or Euro 235). Contact 
[email protected] for details.

Further Reading

Windmill GIS Resources and Applications

  Monitor Issue 30: GPS
  Monitoring Wheel Slip in Trains

  Mapping Dye Dispersion

  Interfacing GPS Receivers

  Seafloor Mapping

  Monitor Issue 30: GPS


Other Resources

  [email protected] Magazine

  US Geological Survey: Geographical Information Systems

Your Applications

If you have used Windmill to log GPS and other data - 
we'd be interested in hearing from you, and possibly 
featuring your application in this newsletter. E-mail 
the editor at [email protected] or fill in the 
form at the bottom of

Excel Corner: 
Finding When the Maximum Data Value was Logged

Suppose you have imported a Windmill Logger file into 
Excel. This file contains data from 1 day, with the time 
each reading was collected in the first column and data 
values in subsequent columns. For example:
A            B
Time         Input A
Secs         volts
18:23:39     1.2186
18:23:40     2.4192
18:23:41     3.5836
18:23:42     4.6947
18:23:43     5.7357
18:23:44     6.6913

You want to find when the largest voltage reading was 
taken. To do this use this formula

Make sure you format the cell containing the above 
formula as a time. Select a Custom cell format of 

How we arrived at the Formula

1. First we want to find the maximum value in column B. 
   To do this we use the MAX function.
   MAX (B:B)
   Using B:B will look through all rows in column B. In 
   our example this returns 6.6913

2. Now we want to determine the location of the value. To 
   do this we use the MATCH function.
   MATCH(lookup_value, lookup_array, match_type)
   Looup_value is the value in which we are interested - 
   the maximum data value.
   Lookup_arrray is the range of cells in which we are 
   Match_type gives options for finding the lookup_value. 
   Match_type can be -1, 0 or 1. For 1, the default, 
   MATCH finds the largest value that is less than or 
   equal to the lookup_value. For 0 MATCH finds the 
   first value that is exactly equal to lookup_value. 
   For -1 MATCH finds the smallest value that is greater 
   than or equal to the lookup_value. 

   In our example the lookup_value is the MAX function, 
   the lookup_array is column B and we want an exact 
   match and so use 0 as the match_type. This gives us
   This returns the row number of the maximum value in 
   column B - row 8 in our example.

3. Finally, we want to show this row's time stamp. To do 
   this we use the INDEX function.
   INDEX(reference, row_num, column_num)
   Reference is one or more cell ranges.
   Row_num is the row from which to return a value.
   Column_num is the column from which to return a value.
   As we are only referencing 1 column, we can dispense 
   with the column_num and we're left with

This example works with Excel 95 and later. For how to 
send data collected by Windmill directly to Excel, see


* Copyright Windmill Software Ltd
* Reprinting permitted with this notice included
* For more articles see

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Windmill Software Ltd, PO Box 58, North District Office,
Manchester, M8 8QR, UK
Telephone: +44 (0)161 833 2782
Facsimile: +44 (0)161 833 2190
E-mail: [email protected]


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