MESXXI : webcam-aided polar alignment

Welcome

Every a bit confirmed amateur-astronomer has already employed the precisely famous "Bigourdan's method " to line up the polar axle of his equatorial setting on the axle of the world, in other words to perform polar alignment of his instrument. It making, he will have undoubtedly could determine weaknesses of technique : empiricism, necessity to make approximations or successive iterations (qualitatively adjust the polar axle azimuth, then its incline, then the azimuth, then the incline, etc), obligation to use stars in definite hour angles (at 0 h in the meridian, at +/-6 h as the star is setting or rising) which sometimes are inaccessible considering the observer's location (observation from a balcony in facade of a building notably) ; stars at +/-6 h are moreover greatly affected by the seeing conditions, and therefore are not suitable for tactful measures of drift. These joint difficulties make that very often a satisfactory polar alignment is obtained only after two or even several nights according to the observer's "feeling", skill or intractability.

In 2003 and 2004 I published in the magazine Astrosurf Magazine a series of articles entitled "Stellar drifts in an equatorial instrument" (numbers 4, 5, 6, 7). The properties of the stellar drifts in an instrument affected by polar alignment defects were analysed there and on this basis two alternative methods were proposed. These original methods (*) allow to dodge all above mentioned obstacles and have following advantages on that of Bigourdan :

Rapidity : alignment defects are determined after the checking of two stars or even of an only one (forget successive approximations)
Safety : quantitative methods founded on a precise theory of drift
Versatility : stars are exploitable whatever are their hour angles (forget the awkward monitoring of stars that are setting or rising)

(*) : they generalize and unify King's and Bigourdan's methods (cf. here and there)

Offered methods suffered however, on practical plan, from three quasi prohibitive disabilities because they imply to perform :

quantitative measures of the drift speeds
the evaluation of the hour angle of each checked off star and, as a result, the sidereal time
trigonometry calculus (not quite compatible with an observation at night even if one has a small adding machine of secondary schools)

Nevertheless, if one observes with an instrument provided with a webcam, and as a result with a computer, signalled disabilities are potentially eliminated, because one then has on one hand an extraordinarily sensitive means of measuring the drift speeds (joint measures of length and distances on the sensor of the webcam) and on the other hand a very powerful computing means which trigonometry impresses not at all. It is of this cogitation that was born software MESXXI, object of the pages which follow.

CONTENTS

Theory and equations (not translated yet)

What about KING's method ? (not translated yet)

Drifts illustrated (not translated yet)

Second order formulas : biases of methods I and II (not translated yet)

Field rotation during a guiding session (not translated yet)

Alignment tolerances for deep sky imaging (not translated yet)

Drifts : lessons from a typical case (not translated yet)

The software (not translated yet)

Review of software (not translated yet)

FAQ (frequently asked questions) (not translated yet)

From Version 4.1.0 (december 2007) MESXXI and MESXXIR are full english/french bilingual softwares

Self-installer files now available (july 2011) for an easy installation within all Windows operating systems including Vista and Seven (32 or 64 bits)
Release of versions 4.1.1 and 5.0.0 of MESXXI and MESXXIR, respectively (november 2011)

Common improvements of MESXXI (4.1.1) and MESXXIR (5.0.0) :

"Reticle" (or "cross-hairs") is now compatible with image aspect ratios differing from 4/3

Elimination of "type 6" errors that could happen formerly

New possibilities of version 5.0.0 (MESXXIR only) :

Automatic preselection of sufficiently bright stars according to time and observer's site

Measurement of pixel aspect ratio (width/height), in case this ratio is unknown

More help during calibration process, by means of contextual messages

Support of "packed" YUV video formats (formats of "macro-pixels" type)

Supported video formats :

"planar" 12 bit per pixel YUV such as IYUV or I420 (MESXXI and MESXXIR)

"packed" 16 bit per pixel YUV such as YUY2 or UYVY (MESXXIR only)

RGB formats (24 bits per pixel) are not supported yet. Detailed Description of YUV formats here on the FOURCC website.

DOWNLOAD section
Softwares mesXXI and mesXXIR may be downloaded below according to two methods :

initial manual method (for Win 98 up to XP only) (now obsolete)

automatic method : preferred method which works on all Windows OS including Vista and Seven (32 or 64 bits)

Preferred automatic method
Download the self-installer files "mes(r)_setup.exe" and execute them. Over Vista and Seven OS the following error message pops up : "\Windows\system32\stdole2.tlb....Failed to register the type library....OLE registry". This message only tells you that the protected file "stdole2.tlb" is already on the computer. Just ignore it to complete the installation. For Vista and Seven OS, mesXXI(r) help files may not readily be displayed : follow the "readme" file instructions to remedy that problem.

Download mesXXI (version 4.1.1)

Download mesXXIR(version 5.0.0)

Initial manual method (Windows 98, 98SE, XP) (for memory)
To install mesXXI or mesXXIr, unzip the .zip file in the directory of your choice (if you install both programs envisage a directory for each) and follow the indications of the "Readme" file. Files with extensions " .dll " and ".ocx" must be copied in directories \WINDOWS\system\ and/or \WINDOWS\system32\ according to the operating system of the machine.

Before using mesXXI or mesXXIR, it is recommended to read attentively their help files, which I tried to make as crystal clear (I hope) as possible : to get help, just open "mesxxi_eng.hlp" or "mesxxir_eng.hlp" files directly or claim help after the launching of software (F1 key or "Help" submenu of "?" menu).

Once a new version of mesXXI or mesXXIR is loaded it is highly recommended, or even imperative, to perform a general reset ("Reset" submenu of the "File" menu).

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MESXXI : measuring and deciphering of stellar drifts