Most pollen analysts today have access to computer facilities for carrying out, at least, basic calculations on their raw data and plotting pollen diagrams. Traditional requirements for the presentation of pollen data in graphical form make it difficult to use commercial graphics packages for the purpose, and most pollen analysts use software written specially for this use. For example, in the 1970s John Birks and Brian Huntley developed POLLDATA for calculation and graphical presentation of pollen data on the Cambridge IBM mainframe. This program was successfully transferred to other mainframes, and now has a PC version. More recently, Eric Grimm's TILIA and TILIAGRAPH, written for PCs, has come into general use in many pollen labs around the world. I have seen and used several such programs (all my Ph.D. thesis work was done with POLLDATA), but over the last few years all my pollen-data crunching and plotting has been done with software that I have written myself: currently I am using a QuickBASIC program called PSIMPOLL. The aims of this note are to outline the way in which PSIMPOLL works, to present the reasons for continuing to use my own software rather than more generally available software, and (most importantly) to act as a reminder that it is possible to write and maintain working programs that suit individuals. Such programs may lack sophistication, but they also lack constraints that are inevitably imposed when using a package that someone else devised and planned.
Commercial packages cannot be used easily to plot pollen diagrams from raw data, but spreadsheets are well-suited to making the calculations. There is little to be gained from writing software for this aspect of pollen data-handling, and I do all my basic calculations on a spreadsheet, exporting the results in the form of an ASCII file. This may then be read by a plotting program directly, or after modification by a suitable text editor. PSIMPOLL provides the first of two steps in plotting results: it reads in calculated pollen data, annotated to indicate data type (percentages, concentrations, etc), and writes as output a PostScript page description file, containing the information needed for a PostScript interpreter to produce the pollen diagram. The second step is the passing of that file to the interpreter and producing the diagram (see Bennett, 1992).
PSIMPOLL reads data from several files: up to four supplied by the user, and up to three that include blocks of text that will form part of the eventual output file. All these files (input and output) are ASCII: readable and modifiable by text editors. The user input files consist of the main data file (essential), and up to three optional files with data on pollen zones, radiocarbon dates, and sediment stratigraphy (using the Troels-Smith notation). The names of the optional files are related to the name of the main data file: PSIMPOLL looks for them, uses them if they are present, and carries on without if they are not.
The format of output can be altered by effects introduced within the main data file, and by selecting options from a menu when PSIMPOLL is run. Within the main data file, a two-character code identifies the data as pollen percentages, concentrations (by volume or weight), accumulation rates, non-pollen data (e.g. magnetic susceptibility data, loss-on-ignition, sediment chemistry, or anything else), or macrofossils. Data may be presented by depth, age, or sample numbers (e.g. for a surface sample dataset). Particular levels, pollen types, or individual data values can be omitted by suitable editing of the dataset. It is also possible to plot different pollen types at different scales, mark certain "types" as charcoal, rarefaction data, rate-of-change data, or to enable PSIMPOLL to recognize a sequence of data for a summary diagram.
PSIMPOLL will either run a dataset immediately using default options, or the user can change the defaults through a menu. These currently include scale factors for plot width and height, style (curves outline or shaded solid), font and font size for text, angle of taxa names, labels and subtitles, selecting taxa for plotting interactively, and joining up curves across missing values (or leaving a gap). The PostScript output is written to a file by default, but can be directed straight to a printer with PostScript interpreter. Output includes sediment stratigraphy, pollen zones, and radiocarbon dates if the necessary data files were present when PSIMPOLL was run. Example output appeared with my note on PostScript in Newsletter 7.
PSIMPOLL is thus a straightforward plotting program. It works reasonably well, and has most features that a pollen analyst will want. It exists because I have found that it suits me to have available a program that I can tinker with: adding, modifying, and deleting features as necessary. I do not have the time to ensure that the program is bug-free, userfriendly, or documented to the standard that would be required for a marketable product, or even one given away free. I fix problems as they occur, or when a colleague complains loudly enough. It copes with the kind of data generated in our group, but I have made no effort to include features that might be found useful by others.
Eventually, accumulated changes will turn the program into enough of a mess that I shall, without compunction and with no feeling of responsibility to users outside our group, retire it, and replace it with something better, as I have done with three predecessors of PSIMPOLL. As well as PSIMPOLL, I have written zonation and pollen rarefaction programs which run from datasets organized in the same way.
If anyone out there wants to try PSIMPOLL, even after reading all this, I will be happy to send them a copy, free, with example data. But I do not guarantee any subsequent service! The newsletter coordinator told me he believes is it useful for the readers to hear about the kinds of software that other individuals and groups are using. After all, that is a purpose of the newsletter; another's solution may help solve a problem of your own. But if you find that the software that you have bought, begged, stolen, or borrowed is limiting, then write your own. Avoid the temptation to bring your own programs up to commercial standards, and you should find that you can quickly produce something that fills your own needs. I have never regretted it.
Bennett, K.D. (1992) Use of PostScript to increase portability of pollen diagrams. INQUA - Commission for the Study of the Holocene, Working Group on Data-Handling Methods Newsletter 7: 6-7.