<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Hi, dear grass-users</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">The new dimensions (principle components) are formed from the eigen vector (1, 2, 3), not of the factor loadings (W). Therefore there is an error in the GRASS-wiki - Principal Components Analysis, the line of code error is copied below:</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div></font><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; "> </span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">## Factor loadings (W=</span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">385.6992, </span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">-364.5920,</span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">37.4824,</span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">636.0665, etc..</span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">) ### </span></div><div><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">###########################################################</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Using the W vector, new maps can be created :</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div></font><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">r.mapcalc 'pc.1 = 385.6992*map.1 +636.0665*map.2 + 474.2358*map.3' </span><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"></font><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">r.mapcalc 'pc.2 = -364.5920*map.1 + 41.8027*map.2 + 240.4573*map.3' </span><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"></font><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">r.mapcalc 'pc.3 = 37.4824*map.1 - 74.7964*map.2 + 69.8356*map.3' </span><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; "><span class="Apple-tab-span" style="white-space:pre"> </span></span></div><div><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; "><br></span></div><div><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; font-size: 13px; line-height: 19px; ">###########################################################</span><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"> </span></div></font><span class="Apple-style-span" style="font-family: Helvetica, Arial, sans-serif; "><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px; ">Correct me if i'm wrong?</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px; "><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px; ">Thanks in advance </span></div></span><font class="Apple-style-span" face="Helvetica, Arial, sans-serif"><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"> </span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">REFERENCES</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">1. Baronti, S., R. Carla, S. Sigismondi & L. Alparone. 1994. Principal component analysis for change detection on polarimetric multitemporal SAR data, Pp: 2152-2154 vol.2154, In: Geoscience and Remote Sensing Symposium, 1994. IGARSS '94. Surface and Atmospheric Remote Sensing: Technologies, Data Analysis and Interpretation, International.</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">2.Fung, T. & E. LeDrew. 1987. Application of Principal Components Analysis to Change Detection. Photogrammetric Engineering & Remote Sensing. 53(12): 1649-1658.</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">3. Singh, A. & A. Harrison. 1985. Standardized principal components. International Journal of Remote Sensing. 6(6): 883-896.</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">------------------------------</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;"><br></span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Gaspar Reyes Póndigo</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Universidad del Mar, Oaxaca, México</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Campus Puerto-Ángel</span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">Carretera principal Puerto Ángel Zipolite km 1.5 </span></div><div><span class="Apple-style-span" style="font-size: 13px; line-height: 19px;">C.P. 70902</span></div><div style="font-size: 13px; line-height: 19px; "><br></div></font></div></div></body></html>