I have vector/topo/image tiled maps for some places in North America which were published as ArcGIS Server REST service. These maps (A) are based in EPSG:26912 projection. Now I want to use these as base map for my OpenLayers web app; besides, I also want to consume other base map sources (B), e.g., OpenStreetmap, Google Maps, ESRI, etc. Since most of these maps are in EPSG:900913 which is spherical Mercator projection to my knowledge, if I just add these base map layers into OpenLayers map component, the group A and group B won't overlay correctly, which means they are displayed as separate maps.
I know this is something related to projection, and might need some code with proj4js, however, as a newbie, I don't really know what to start with.
Basically, I want to put OSM/Google maps as the base map for the whole world in tier 1, then put EPSG:26912 base maps for some places in North America in tier 2, and put other WMS or WFS in the top tier.
do I need to transform EPSG:26912 to EPSG:900913 or opposite? I guess I should use EPSG:900913 as the base projection.