Bloodsong Termagant 10 Posted August 2 i think i figured out what i'm doing wrong. i am trying to calculate the angle of a slope between two points. point 1 = the spot directly below the avatar where it is standing. (in region coordinates) point 2 = the spot the ray intersects the ground ahead of the avatar. (in region coordinates, translated from the avatar's local forward axis) and i have this formula: angle = RAD_TO_DEG*( llAtan2( (p2.z - p1.z),(p2.x - p1.x) )); i THINK the problem is, that i'm just using the X and Z coordinates, and not correcting for the Y coordinate, if the avatar is not facing along the global X axis. so i found this: https://www.euclideanspace.com/maths/geometry/elements/projections/index.htm how to project a point (my target hit with x,y coordinates) onto a line (the global x axis). um... okay, so i have to take the line that is the avatar's facing, project a line at a right angle to that line from the point, and find out where it hits the X axis. uh... yeah, i dunno how to do that :/ except by drawing on graph paper! :X drawing: https://prnt.sc/onjtdl okay, i worked THIS out: http://prntscr.com/onk6ao if i can just get the x/y plane distance of a, then calculate the x/y coordinate of 2a along the avatar facing... THAT x coordinate should be the one i need. and i don't need to mess around with all those pythagorean thingies. what's the 2d version of llVecDist? oh, set the Zs to 0 first... okay, i came up with this, and it returns total BS. it even returns different answers if i click it (activate the calculation by touch) multiple times, without moving in between. float getSlope() { float ht = 0.75; //--normally a calculated global. vector pos = llGetPos(); //--we know where the floor is, cuz we're standing on it @ -ht. vector target = pos; rotation rot = llGetRot(); target = pos + <3.*ht,0.,0.> *rot;//-- test 3 ahead and 2.5 down target.z = target.z - 2.5*ht; // llOwnerSay("Aiming "+(string)pos+" to "+(string)target); list res2 = llCastRay(pos, target, [RC_REJECT_TYPES, RC_REJECT_AGENTS | RC_REJECT_PHYSICAL, //RC_DATA_FLAGS, RC_GET_NORMAL, RC_MAX_HITS, 1]); llOwnerSay("RC returned:"+llDumpList2String(res2, ",")); float angle; if(llList2Integer(res2, -1) != 0) { vector p1 = pos; vector p2 = llList2Vector(res2, 1); //--calculate X without Y vector xy1 = p1; vector xy2 = p2; xy1.z = 0.0; //--get rid of Z influence xy2.z = 0.0; float dist = llVecDist(xy1,xy2); vector xTarget = pos + <2*dist, 0., 0.> * rot; //--SLOPE: p1.z -= ht; //--make this the floor p1.x = xTarget.x; //--make this our actual distance along avatar FWD angle = RAD_TO_DEG*( llAtan2( (p2.z - p1.z),(p2.x - p1.x) )); } else //--we didn't hit anything, the slope is WAY down. angle = -45.0; //--midway to down. fudged. if(angle > 90.0) angle -= 180.0; else if (angle < -90.0) angle += 180.0; return angle; } and no, i don't know how to do angle math, either :X Quote Share this post Link to post Share on other sites

Rolig Loon 21,484 Posted August 2 You seem to be overthinking things. Try this ... default { touch_start(integer total_number) { vector vHere = llGetPos(); // Here I am float fGroundHere = llGround(ZERO_VECTOR); // Here's the ground under me vector vThere = llGetPos() + <20.0,0.0,0.0>*llGetRot(); // This is 20 m in front of me float fGroundThere = llGround(vThere - vHere); // This is the ground 20 m in front of me float fDist = llVecDist (<vThere.x,vThere.y,fGroundHere>,<vHere.x,vHere.y,fGroundHere>); // Here's the horizontal distance between the spots float fSlope = llAtan2((fGroundThere - fGroundHere), fDist ); // And here's the calculated slope llSay(0, "Slope in radians = " + (string) fSlope + " Slope in degrees = " + (string)(fSlope*RAD_TO_DEG) ); } } You'll have to make appropriate adjustments if the surface under you isn't the land surface, but the principle will be the same. Quote Share this post Link to post Share on other sites

animats 1,979 Posted August 2 1 hour ago, Bloodsong Termagant said: i am trying to calculate the angle of a slope between two points. Unclear what that means. Two points do not define an angle. It takes three points. You want ground slope, right. OK. vector p1; // point on ground under avatar vector p2; // point on ground ahead of avatar .... vector movedir = llVecNorm(p2-p1); // direction moving between points float zlen = movedir.z; // height of triangle float xylen = llVecMag(<movedir.x, movedir.y,0>); // base of triangle float slopeangledeg = RAD_TO_DEG*llATan2(zlen, xylen); // ground slope as an angle in degrees. // Traditional slope (1 m rise in 10 m horizontal => 0.1 slope) if you want that float slope = zlen / xylen; // but will divide by 0 if vertical. Quote Share this post Link to post Share on other sites

Kyrah Abattoir 1,375 Posted August 4 We have a pretty well furnished library of geometry function here: http://wiki.secondlife.com/wiki/Geometric 2 1 Quote Share this post Link to post Share on other sites

Bloodsong Termagant 10 Posted August 7 OH THANK GOODNESS! i saw that what i was doing was TOTALLY wrong... especially as y approached zero... thank you so much, for helping me untangle THAT mess. i'm still trying to picture what's going on... but the formula is working! and i will definitely have to bookmark that, kyrah! 1 Quote Share this post Link to post Share on other sites